**MEPAG**

**Report from the**

**2013 Mars Science Orbiter (MSO)**

**Second Science Analysis Group**

May 2007

*Version 29 May 2007*

*This report has been approved for public release by JPL Document Review
Services (CL#07-1764) and may be freely circulated.*

Recommended bibliographic citation:

MEPAG MSO-SAG-2 (2007). Report from the 2013 Mars Science Orbiter (MSO)
Second Science Analysis Group, 72 pp., posted June 2007 by the Mars
Exploration Program Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>.

or

Calvin, W. et al., (2007): Report from the 2013 Mars Science Orbiter
(MSO) Second Science Analysis Group, 72 pp., posted June 2007 by the
Mars Exploration Program Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>.

Inquiries regarding this report should be directed to Wendy Calvin
<wcalvin@unr.edu>, <Richard.W.Zurek@jpl.nasa.gov>, or Michael A. Meyer
(mmeyer@mail.hq.nasa.gov)

[]{#__RefHeading___Toc42082052 .anchor}Members

Wendy M. Calvin, Chair - University of Nevada, Reno

Mark Allen, Jet Propulsion Laboratory/Caltech

W. Bruce Banerdt, Jet Propulsion Laboratory/Caltech

Don Banfield, Cornell University

Bruce A. Campbell, Smithsonian Institution

Phil R. Christensen, Arizona State University

Ken S. Edgett, Malin Space Science Systems (resigned 4/18/07)

Bill M. Farrell, NASA Goddard Space Flight Center

Kate E. Fishbaugh, International Space Science Institute

Jim B. Garvin, NASA Goddard Space Flight Center

John A. Grant, Smithsonian Institution

Alfred S. McEwen, University of Arizona

Christophe Sotin, University of Nantes

Tim N. Titus, U. S. Geological Survey

Daniel Winterhalter Jet Propulsion Laboratory/Caltech (Study Scientist)

Richard W. Zurek, Jet Propulsion Laboratory/Caltech (Mars Program
Office)

**Project Support at JPL**

Fernando Abilleira

Jan Chodas

Marie Deutsch

Corey C. Harmon

Stuart Kerridge

Robert Kinsey

Tomas A. Komarek

P. Douglas Lisman

Nino Lopez

Ron Salazar

Troy Schmidt

Joanne Vozoff

Acknowledgement:

The SAG activity described in this report was supported by the Jet
Propulsion Laboratory, California Institute of Technology, under a
contract with the National Aeronautics and Space Administration.

Contents

**Members [i](#__RefHeading___Toc42082052)**

Charter [v](#__RefHeading___Toc42082053)

Executive Summary [1](#__RefHeading___Toc42082054)

1 Background [3](#__RefHeading___Toc42082055)

2 Deliberations/Process [3](#__RefHeading___Toc42082056)

3 Core MSO Mission Attributes [4](#__RefHeading___Toc42082057)

4 Themes [4](#__RefHeading___Toc42082058)

5 Science Scenarios [5](#__RefHeading___Toc42082059)

6 Science Goals By Group [7](#__RefHeading___Toc42082060)

6.1 Atmospheric Science [7](#atmospheric-science)

6.1.1 Atmospheric Signatures [7](#atmospheric-signatures)

6.1.1.1 Background [7](#background)

6.1.1.2 Goals [9](#goals)

6.1.1.3 Measurement Priorities [9](#measurement-priorities)

6.1.2 Atmospheric State: Orbital Science
[11](#atmospheric-state-orbital-science)

6.1.2.1 Background [11](#background-1)

6.1.2.2 Goals [12](#goals-1)

6.1.2.3 Measurement Priorities -- 1: Extend the Climatology
[12](#measurement-priorities-1-extend-the-climatology)

6.1.2.4 Measurement Priorities -- 2: New observations for model
validation
[12](#measurement-priorities-2-new-observations-for-model-validation)

6.1.2.5 Synergies [13](#synergies)

6.1.3 Atmospheric State: Landed Science
[13](#atmospheric-state-landed-science)

6.1.3.1 Background [13](#background-2)

6.1.3.2 Goals [13](#goals-2)

6.1.3.3 Measurement Priorities [14](#measurement-priorities-1)

6.1.3.4 Synergies [15](#synergies-1)

6.2 Polar Processes and Modern Climate
[19](#polar-processes-and-modern-climate)

6.2.1 Background [19](#background-3)

6.2.1.1 Seasonal polar ice caps [19](#seasonal-polar-ice-caps)

6.2.1.2 Residual polar ice caps [20](#residual-polar-ice-caps)

6.2.1.3 Polar Layered Deposits (PLD) [21](#polar-layered-deposits-pld)

6.2.1.4 Mid-latitude Glacial and Periglacial deposits
[22](#mid-latitude-glacial-and-periglacial-deposits)

6.2.2 Priority Goals and Measurements
[23](#priority-goals-and-measurements)

6.2.2.1 Topography and deposit volume
[23](#topography-and-deposit-volume)

6.2.2.2 Mass and Energy Balance [24](#mass-and-energy-balance)

6.2.2.3 Stratigraphy and Mantling [25](#stratigraphy-and-mantling)

6.3 Geology: Near-surface Science [28](#geology-near-surface-science)

6.3.1 Overview [28](#overview)

6.3.2 Ancient Environments [28](#ancient-environments)

6.3.3 Dynamic Mars/Mars Today [29](#dynamic-marsmars-today)

6.3.4 Priority Measurements [31](#priority-measurements)

6.4 Geophysics: Landed and Interior Science
[35](#geophysics-landed-and-interior-science)

6.4.1 Background [35](#background-4)

6.4.1.1 Importance of Interior Investigations for Mars Science
[35](#importance-of-interior-investigations-for-mars-science)

6.4.1.2 Single Station vs. Network Measurements
[36](#single-station-vs.-network-measurements)

6.4.2 Priority Goals and Measurements
[38](#priority-goals-and-measurements-1)

6.4.2.1 Seismic Activity and Impact Frequency
[38](#seismic-activity-and-impact-frequency)

6.4.2.2 Crustal Structure [39](#crustal-structure)

6.4.2.3 Mantle Structure [39](#mantle-structure)

6.4.2.4 Core Structure [40](#core-structure)

6.4.2.5 Thermal State [40](#thermal-state)

7 Strawman Instruments [42](#__RefHeading___Toc42082102)

7.1 Solar occultation FTIR [42](#solar-occultation-ftir)

7.2 Sub-millimeter spectrometer [42](#sub-millimeter-spectrometer)

7.3 "MARCI-like" Camera [43](#marci-like-camera)

7.4 Thermal IR or "Lite" spectrometer system
[43](#thermal-ir-or-lite-spectrometer-system)

7.5 "HiRISE" Class Imager (HCI) [43](#hirise-class-imager-hci)

7.6 Multibeam Lidar Altimeter + Ultra Stable Oscillator
[44](#multibeam-lidar-altimeter-ultra-stable-oscillator)

7.7 Multi-spectral SWIR/TIR or "Capable" Spectrometer
[44](#multi-spectral-swirtir-or-capable-spectrometer)

7.8 1-m resolution camera [45](#m-resolution-camera)

7.9 Synthetic Aperture Radar [45](#synthetic-aperture-radar)

7.10 Landed Geophysics [45](#landed-geophysics)

7.11 Landed Meteorology [46](#landed-meteorology)

8 Mission Scenarios [47](#__RefHeading___Toc42082114)

8.1 Plan A: Atmospheric Signatures and Near-Surface Change
[48](#__RefHeading___Toc42082115)

8.2 Plan P: Polar and Climate Processes
[50](#plan-p-polar-and-climate-processes)

8.3 Plan G: Geological and Geophysical Exploration
[51](#plan-g-geological-and-geophysical-exploration)

8.4 International Cooperation [52](#international-cooperation)

9 MSO Project Analysis [53](#__RefHeading___Toc42082119)

9.1 Mission Design Summary [53](#mission-design-summary)

9.2 Key Spacecraft Configuration Options
[54](#key-spacecraft-configuration-options)

9.3 Mission Design Trades [55](#mission-design-trades)

9.3.1 Solar Occultations Study [56](#solar-occultations-study)

9.3.2 Lander Accessibility [59](#lander-accessibility)

9.4 MSO Implementation [59](#mso-implementation)

9.5 Schedule [60](#schedule)

9.6 Summary [60](#summary)

10 Observations in Support of Future Exploration
[60](#__RefHeading___Toc42082128)

10.1 Landing Site Hazard Assessment
[60](#landing-site-hazard-assessment)

10.2 Atmospheric Environment for Flight Aerodynamics
[61](#atmospheric-environment-for-flight-aerodynamics)

10.3 Precursor measurements for future human exploration
[63](#precursor-measurements-for-future-human-exploration)

11 Discussion and Issues [65](#__RefHeading___Toc42082132)

11.1 Science Issues [65](#science-issues)

11.1.1 Subsurface Imaging [65](#subsurface-imaging)

11.1.2 Methane detection and traceability
[65](#methane-detection-and-traceability)

11.1.3 Higher Spatial Resolution than HiRISE
[66](#higher-spatial-resolution-than-hirise)

11.1.4 Seismic detection. [66](#seismic-detection.)

11.1.5 Landed Science Priority [67](#landed-science-priority)

11.1.6 Neutron spectroscopy [67](#neutron-spectroscopy)

11.2 Technical/Cost Issues [67](#technicalcost-issues)

11.2.1 Trades Involving a Landed Drop Package
[67](#trades-involving-a-landed-drop-package)

11.2.2 Budget Reserves [68](#budget-reserves)

11.2.3 Funding of Science Activities during Development (Phases A-D)
[68](#funding-of-science-activities-during-development-phases-a-d)

12 Conclusion [68](#__RefHeading___Toc42082144)

References [69](#__RefHeading___Toc42082145)

List of Acronyms [70](#__RefHeading___Toc42082146)

[]{#__RefHeading___Toc42082053 .anchor}Charter

**Mars Science Orbiter Science Analysis Group-2 (MSO-SAG-2)**

[Introduction]{.underline}

In 2006, the Mars Exploration Program asked MEPAG to prepare an analysis
of a Mars science orbiter that could be launched in 2013. This analysis
was carried out by means of a Science Analysis Group (MSO SAG-1). SAG-1
started with the following assumptions:

-   Assume that the mission has an orbital element, and that for
    telecommunications purposes, a lifetime requirement of at least 10
    years will be imposed.

-   Assume the mission is constrained to a total budget no larger than
    the escalated equivalent of the budget of MRO. (Notwithstanding this
    assumption, the SAG may consider mission concepts whose scope
    extends beyond an MRO class mission, particularly if they result in
    a lot more science for only a little more money.)

The SAG-1 concluded that a very attractive mission could be configured
with aeronomy and trace gas measurements (Farmer et al., 2006), and a
baseline configuration was proposed.

On Jan. 8, 2007, NASA announced that it had narrowed its selection for
the 2011 Scout mission to two possibilities, MAVEN and TGE, both of
which are primarily aeronomy missions (and also with some other
measurements). Therefore, aeronomy science is no longer appropriate as a
focus for the 2013 Mars Science Orbiter. Hence, the Mars Exploration
Program requests a new analysis of the science options for MSO, hereby
termed MSO-2.

# Science Scope for this Analysis {#science-scope-for-this-analysis .unnumbered}

As the Mars Exploration Program is a science-driven and discovery
responsive program, the SAG-2 should consider addressing more recent
findings from Mars missions such as those related to contemporary gulley
formation and cratering rates. For the revised analysis, SAG-2 will use
the same telecommunications and financial assumptions as the original
SAG-1 (listed above). Although the scientific scope is not restricted,
an analysis of the following options is specifically requested:

-   [Orbital camera(s).]{.underline} Science that can be carried out
    using one or more cameras that would also be available to support
    evaluation of landing site safety for future landed missions.

-   [Atmospheric trace gas.]{.underline} The spatial variation in trace
    gases in the Martian atmosphere, including methane. This was studied
    by the SAG-1 and their analysis should prove useful in considering
    different mission concepts.

-   [Orbital geophysics]{.underline}. Any class of orbital geophysics
    that can be mapped to high-priority MEPAG objectives may be
    considered.

-   [Landed geophysical package]{.underline}. The Mars Advance Planning
    Group (MAPG) in its 2006 Update Report identified the option of
    including a single geophysical lander on MSO. "A case can be made
    that a geophysical pathfinder would generate some valuable science
    (although not nearly as valuable as a 4-node geophysical network)
    (MAPG, 2006; p. 10). The SAG-2 should consider the possibility of
    one or more landed elements to be launched in 2013, and also the
    potential to achieve meaningful network science through additional
    landed elements to be launched at later opportunities,

[Requested Tasks]{.underline}

1.  Determine the primary combinations of the above classes of science
    investigations that fit within the overall assumed cost and
    engineering constraints, and that constitute possible mission
    concepts.

    a.  Estimate the orbital parameters for the different mission
        concepts.

    b.  Analyze the trades between the science and telecommunications
        objectives (e.g. orbits, phasing) for each mission concept

2.  Analyze the degree of alignment of the different mission concepts
    with the NRC's Decadal Survey and with MEPAG's priority system and
    the MEPAG Goals document.

3.  It is not necessary to develop a comparative prioritization of the
    multiple mission concepts. The SAG-2 analysis work will constitute
    input to a HQ-chartered Science Definition Team, who will evaluate
    the relative priorities.

4.  [Human precursor measurements.]{.underline} Consider the
    implications of the different mission concepts for the eventual
    human exploration of Mars, and identify the potential opportunities
    for contributions from other NASA Directorates. Presumably,
    measurements made to support the preparation for human exploration
    can also be applied to scientific objectives.

5.  [Engineering support for future missions]{.underline}. In addition
    to telecom relay capability, consider whether there are other
    engineering-related measurements that would be of value to the Mars
    Exploration Program's future mission. For example, how important is
    a system that can monitor the upper atmospheric density to allow
    aerobraking or aerocapture of missions in the second half of the
    decade?

# Methods {#methods .unnumbered}

-   SAG-2 will conduct their business primarily via telecons, e-mail,
    and/or web-based processes. One to two face-to-face meetings may be
    accommodated if needed.

-   If added expertise is needed, SAG-2 can consider requesting a
    briefing or possibly adding the person to the SAG.

-   The SAG will be supported by a small group of JPL mission engineers
    in their consideration of potential costs. 

-   Logistical support will be provided by the Mars Science Office at
    JPL.

[Timing]{.underline}

-   The SAG will begin its discussions as soon as possible. A draft
    report will be reviewed by the MEPAG Executive Committee and by MEP
    is requested by April 15, 2007.

-   A midterm status check by Michael Meyer, David Beaty, and Ray
    Arvidson is requested by about March 1, 2007.

-   A final report is requested by May 15, 2007.

[Report Format]{.underline}

-   The SAG-2 report of findings will be presented in the form of both a
    PowerPoint presentation and a text white paper. Additional
    supporting documents may need to be prepared. After the report has
    been accepted by program management (including MEPAG Executive
    Committee), it will be posted on a publicly accessible website.

-   The report will not contain any material that is ITAR-sensitive.

[References]{.underline}

Farmer, B., et al., 2006, Mars Science Orbiter (MSO): Report of the
Science Analysis Group, Unpublished white paper, 48 p, posted April 2006
by the Mars Exploration Program Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>.

Mars Advance Planning Group (2006), 2006 Update to "Robotic Mars
Exploration Strategy 2007-2016," Unpublished white paper, 24 p, posted
Nov. 2006 by the Mars Exploration Program Analysis Group (MEPAG) at
[**http://mepag.jpl.nasa.gov/reports/index.html**](http://mepag.jpl.nasa.gov/reports/index.html).

Michael Meyer, NASA Senior Scientist for Mars Exploration, NASA HQ

David Beaty, Mars Program Chief Scientist, JPL

Ray Arvidson, MEPAG Chair

January 18, 2007

[]{#__RefHeading___Toc42082054 .anchor}Executive Summary

A scientifically bold orbital mission in 2013 can address profound and
basic scientific gaps that remain in the era beyond MRO. Not
surprisingly, there is no single instrument complement that addresses
all of the highest priority science, and the science analysis group
identified three primary mission scenarios that would address multiple
objectives. The high priority measurements are each traceable to MEPAG
and NRC goals. These measurements are directly linked to the requested
science study areas of the Charter and other areas where critical gaps
in current knowledge exist.

All three scenarios address a theme of "Dynamic Mars: Activity,
Transport and Change". Any one of these three scenarios will return
significant new information relevant to our understanding of the planet,
its history and its potential for life.

-   ***Plan A: Atmospheric Signatures and Near-Surface Change:*** This
    plan addresses the charter task to examine relatively short-lived
    atmospheric trace gases and follows up on discoveries of recent
    surface activity, such as new gullies. The intention is to provide a
    comprehensive characterization of the chemical composition of the
    Martian atmosphere, its global distribution and variation with
    season, with particular sensitivity for the ultra-low abundance
    species that might be signatures of subsurface processes related to
    existing habitable zones and possible life. The record of global
    climate measurements of atmospheric temperature, dust, water vapor,
    and surface albedo would be continued while providing new
    measurements, such as direct measurements of wind, that uniquely
    constrain and validate models of atmospheric dynamics and transport.

-   ***Plan P: Polar and Climate Processes:*** This plan approaches the
    orbital imaging and geophysics elements of the charter through the
    lens of the dynamics of volatile reservoirs and modern climate. This
    scenario follows up on discoveries of active erosion of the residual
    south CO~2~ ice cap and anticipated new results from the 2008
    Phoenix polar lander. The focus is a detailed examination of the
    mass/energy balance through monitoring of both poles in space and
    time. Precise elevation and volume of seasonal and residual volatile
    deposits will allow a time variable measure of mass in exchange with
    the atmosphere and estimates of exchange with lower latitude
    volatile reservoirs at different epochs. The record of global
    climate measurements, particularly albedo and temperature relevant
    to energy balance, will be continued and new direct measurement of
    winds will improve models of surface-atmosphere interactions at all
    latitudes.

-   ***Plan G: Geological and Geophysical Exploration:*** This plan
    satisfies specific Charter requests to examine high-resolution
    imaging, orbital geophysics, and a landed geophysical package. The
    plan would follow up on discoveries such as the present-day (last
    decade) impact events and debris flows associated with gully
    activity. The first exploration of the uppermost few meters of
    regolith and mantling materials, and topographic change detection
    over broad regions is provided. The landed package would address
    high priority interior objectives such as seismic activity and
    structure of the crust, mantle and core, in addition to surface
    measurements of temperature, water vapor and dust electrification in
    the planetary boundary layer.

**The SAG did not prioritize amongst the three scenarios, in that:**

-   No single scenario can complete the remaining significant orbital
    science to be accomplished in the wake of MRO.

-   Each scenario addresses key (but different) MEPAG goals.

-   All scenarios feed-forward to missions currently under study for
    2016, 2018 and 2020 (e.g., Network, Sample Return, Astrobiology
    Field Lab, Mid-range Rovers) and to support of planning for human
    exploration, although each scenario has stronger ties to some
    missions than others.

**Variations of these three thematic scenarios were then grouped into
three tiers of mission science, based on completeness, synergy, and ROM
costs:**

-   ***Core Mission Concept (CMC):*** This level provides the best
    combination of investigations focusing on one of the above science
    scenarios while keeping key cross-disciplinary elements and staying
    within reasonably constrained resources of mass and cost.

-   ***Augmented:*** These scenarios added another complementary science
    thrust to the CMC. These options were in line with the MRO-class
    flight system capabilities but would require significantly increased
    funding and/or contributed elements to achieve the expanded suite of
    science objectives.

-   ***Reduced:*** This level is consistent with the nominal cost target
    provided by the project. However, the SAG judged these options to be
    much less desirable as they required significant compromises with
    regard to measurement goals or supported too few cross-disciplinary
    elements.

**Findings:**

-   The SAG strongly preferred the Core Mission Concepts over the
    "reduced" options, since the gain in science for the modest
    augmentation was very high and preserved the cutting-edge
    cross-disciplinary elements that are the hallmark of a core mission.

    -   To this end, no single component should dominate the payload,
        and a landed element should not preclude significant, innovative
        orbiter science.

-   A single lander emphasizing geophysical measurements (including
    meteorology) is scientifically credible and could be
    paradigm-shifting. However, the notional lander system presented to
    the SAG appears to be inadequate in cost and mass.

-   The implementation required by each scenario is sufficiently
    different (e.g., orbital inclination or possible inclusion of a
    landed component) that it will require an early selection amongst
    the three scenarios.

-   International contributions could help with cost, but they (or their
    requirements) need to be carefully reviewed to ensure that key
    measurements will be met.

**Programmatic Decisions Required Prior to the Science Definition Team
(SDT)**

-   Is the drop-package to be a key component of the MSO mission?

-   On which scenario should the SDT focus?

-   What cost and mass resources will be baselined for MSO?

1.  []{#__RefHeading___Toc42082055 .anchor}Background

In the winter of 2005/2006, a Science Analysis Group (SAG-1), chaired by
C. B. Farmer was convened to examine the 2011/2013 launch opportunity.
That group deliberated via telecon and email and delivered a final
report in March of 2006 that analyzed science goals focused on the
atmospheric evolution of Mars through study of the exosphere and
atmospheric escape, and the composition and circulation of the lower
atmosphere (available via the MEPAG web site
http://mepag.jpl.nasa.gov/reports/MSO_SAG_report_071006.pdf). The
primary measurements emphasized characterization of loss of water to
space through the upper Mars atmosphere, complemented by measurements of
key biogeochemical gases (particularly methane) in the lower Mars
atmosphere, possibly identifying local areas for future landed
exploration. The cost of mission, with straw-man payload, was included
in 2006 POP guidelines and was carried over to 2007.

In January of 2007, two Mars Scout investigation teams, both focusing on
the upper atmosphere processes and escape to space, were selected for a
head-to-head competition for the 2011 launch opportunity. A new Science
Analysis Group (SAG-2) was formed to re-evaluate scientific options for
the 2013 launch opportunity. The Charter for the SAG-2 is provided as a
preface to this document.

2.  []{#__RefHeading___Toc42082056 .anchor}Deliberations/Process

Calvin agreed to Chair the SAG-2 in the latter part of January 2007. In
consultation with the executive committee, Michael Meyer, Dave Beaty and
Ray Arvidson, committee members were selected to address the specific
scientific analysis requested in the Charter as well as span the breadth
and diversity of Mars science under consideration. The group was under a
rapid timeline to deliver a final report in 3.5 months in order to
expedite the process through Science Definition Team (SDT) and
Announcement of Opportunity (AO) with a desired release date in early
2008. The group met weekly by teleconference from Feb 7 to May 16, 2007
and 8 members of the SAG-2 met for a face-to-face meeting at the annual
Lunar and Planetary Science Conference in March.

On average, each weekly telecon was attended by 13 of the 16 SAG members
though participation in any given week varied. In March and April
several additional Friday or Monday phone meetings were scheduled but
with lighter attendance. Calvin distributed comprehensive written notes
after each meeting so that those unable to attend would be up to speed
with the conversation. In addition, a lively and extensive email
exchange occurred, with between 15 and 50 emails traded each week on a
variety of topics.

The initial meeting allowed the SAG-2 to discuss the Charter and basic
mission constraints with the Executive committee and the Mars Science
Orbiter (MSO) project office, represented by Tom Komarek and Daniel
Winterhalter as the Study Scientist and liaison to the project.

Early conversations outlined properties that should be representative of
a program core mission (Section 3) as well as discussed overarching
themes (Section 4) that are relevant given the wealth of new information
and discovery in the past decade of Mars exploration. A comprehensive
list of forward-thinking science goals was developed by the entire SAG-2
(Section 5). These goals incorporated the specific science analysis
requests in the Charter. Given the emphasis on volatiles in the recent
NRC decadal survey, an additional major set of goals in the area of
polar processes emerged. In order to focus the dialog on the next
critical measurements the SAG-2 was split into four sub-groups along
discipline lines, where the key measurements were further refined
(Section 6). High priority measurements were defined and strawman
payload instruments were identified that can accomplish the measurement
goals (Section 7). Numerous potential combinations of instruments were
considered and the SAG-2 ultimately reduced these to three scenarios
with science synergies, diverse feed-forward ability and within the
evolving cost guidelines that were provided to the SAG-2. These
scenarios are described in Section 8. The MSO project looked at one of
these scenarios in light of mission implementation (Section 9), though
specific mission trades will need to be explored in more detail by the
SDT. In Section 10 we consider how these scenarios will support future
(including human) exploration. Specific science issues that were
discussed, some of which were resolved, and others not, is given in
Section 11. We conclude (Section 12) that there is ample innovative
science to be done in orbit at Mars.

3.  []{#__RefHeading___Toc42082057 .anchor}Core MSO Mission Attributes

An outcome of early discussions was to classify properties that
distinguish a core Mars Exploration Program (MEP) mission from competed
Scouts and smaller focused objectives. The SAG-2 agreed to the following
guidelines to help define mission scenarios and combinations of science
goals.

1)  Ability to address multiple science objectives with a wide range of
    potential instruments. Measurements/Instruments are linked either
    through a broad theme or through synergy available among
    observations.

2)  Strawman payload should not be over-specified, but provides
    feasibility and allows creative solutions to achieve the desired
    science objectives to arise from the community.

3)  Provides the opportunity to do science that is "too big" for
    Discovery or Scouts.

4)  Either makes a new measurement, not previously done at Mars, or
    augments existing measurements such that the data can provide a
    paradigm shift or significant advance in our understanding of the
    planet.

5)  Makes a significant step or definable progress against programmatic
    goals by either building on past discoveries or enabling future
    strategic missions.

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4.  []{#__RefHeading___Toc42082058 .anchor}Themes

The group considered a number of overarching scientific themes that
might serve to steer the Mars Exploration Program in the decade
following the ongoing and highly successful "Follow the Water" campaign.
It is clear that this goal has indeed resulted in multiple locations
where water has been shown to have interacted extensively with the rock
record and identified high priority candidates for future landed
missions. Among the broad themes discussed were those of habitability or
habitable zones, dynamics or contemporary processes including
atmospheric, polar and geologic processes, ancient environments, and
evolution of a livable planet. In addition to these themes, a list of
more specific topics was generated with regard to specific science or
measurement objectives. These topics are outlined in the next section.

5.  []{#__RefHeading___Toc42082059 .anchor}Science Scenarios

A number of high priority observations are identified in various MEPAG
and NRC documents. Most recently, the Mars Advanced Planning Group
(MAPG) published a detailed report on the strategy for robotic
exploration of Mars followed by an update in response to review by the
NRC (MAPG 2006). Additional detailed goals are outlined in the MEPAG
"Goals" document
(http://mepag.jpl.nasa.gov/reports/MEPAG%20Goals_2-10-2006.pdf), and
numerous reports from COMPLEX and the Space Studies Board. The SAG-2
operated under the ground rules that the Mars Reconnaissance Orbiter
(MRO) would achieve its minimum mission success criteria and we would be
focusing on new science that would meet well-established priorities from
these and earlier reports. Due to the competition sensitive nature of
the 2011 Scout missions the SAG-2 was not provided with any additional
information other than what was in the press release regarding the
selection for Phase A studies. Our assumption was that neither MAVEN nor
TGE would fully address either the measurement goals associated with
trace gasses or lower atmosphere circulation and these remained as
important components of our science deliberations. Discussions first
focused on defining new science requirements before getting into the
details of the mission technical implementation.

A period of "idea generation" via phone and email generated a fairly
expansive list of science topics that would be fruitful in the post-MRO
decade and these were further winnowed into science scenarios that were
felt to be the most immediately compelling. A brief outline is provided
here. In Section 6 a detailed description of specific observations,
measurement goals and justification for each objective is provided.

1)  **Atmosphere and Climate:** The high priority goals identified both
    in MAPG 2006 and in the SAG-1 report include following the MSL
    mission with the ability to globally map and locate potential
    sources of methane and other trace gasses, as well as detailed
    observation of the near-surface meteorology and atmospheric boundary
    layer conditions.

    a.  Atmospheric Composition (Signatures) and Transport

        i.  Trace gas constituents

        ii. Sources

        iii. Dynamics (Transport)

    b.  Climatological Monitoring and Atmospheric Processes

        i.  Modern Climate and Global weather

        ii. CO2, Water, Dust cycles (winds)

        iii. Interannual Variations

        iv. Regional surface changes (coupled to climate)

2)  **Polar, Glacial and Periglacial Processes:** As outlined in the
    MAPG 2006 report, a quantitative understanding of surface-atmosphere
    fluxes and thermal balance will require higher temporal observations
    than afforded by the short-lived 2008 Phoenix lander. The SAG-2
    developed a set of specific objectives to address the broad
    questions emerging from the polar community, specifically:

    a.  Mass and energy budgets and nature and time scales of processes
        which control these

    b.  Volatile and dust exchange between polar and non-polar
        reservoirs and relation to past and present distribution of
        subsurface ice

    c.  Physical characteristics and relationship between geologic units

    d.  Chronology, compositional variability, and record of climate
        change in the layers

    e.  Age of the PLD and glacial, fluvial, depositional, erosional,
        flow history

Although the MAPG report treats both structure and interior of Mars and
surface and near-surface processes under the "Geology" theme, the SAG-2
divided this into two working groups, consistent with the charter to
explore landed geophysics and orbital geophysics as separate elements.

3)  **The surface rock record aka "Geology":** These areas all link to a
    general understanding of the surface and shallow subsurface geologic
    record, and its implications for past/present climate and
    habitability. The SAG-2 concentrated on the next generation of
    measurements that target particular issues and can be performed from
    orbit \-- subsurface imaging and improved spatial or spectral
    coverage by imagers and spectrometers.

    a.  Ancient Environments

        i.  Sedimentary rock depositional setting

        ii. Stratigraphic relationships (sedimentary and igneous)

        iii. Burial and exhumation of landforms and cratered surfaces

    b.  Contemporary Processes (Dynamic Mars)

        i.  Gullies (Fluvial and mass-wasting)

        ii. Polar landform change

        iii. Physical properties of the upper layers of PLD

        iv. Links between hydrogen signature and near-surface features.

        v.  Aeolian processes

        vi. Surface deformation or active endogenic processes

        vii. Current impact rate and surface age

4)  **Inside Mars aka "Geophysics":** Network science and interior
    geophysical measurements have been a recognized priority in Mars
    Architecture and NRC documents for several decades. In particular a
    surface network of sensors was recognized as one the "next best
    steps" for the Geology goal in the MAPG 2006 report and the SAG-2
    concentrated on what could be accomplished with a single landed
    package that would feed-forward to network science at a future date.

    a.  Size, density and state (solid or liquid) of the core

    b.  Thickness, density and stratification of the crust

    c.  Density and layer of the mantle

    d.  Seismic activity (frequency and distribution)

    e.  Heat flow and lithosphere thickness (both related to thermal
        gradient)

```{=html}
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```
6.  []{#__RefHeading___Toc42082060 .anchor}Science Goals By Group

From the outline in the previous section, discipline sub-groups of the
SAG-2 further refined the specific observations and their links to
MEPAG, MAPG and NRC documents.

## Atmospheric Science 

Atmospheric Science for MSO is comprised of two major scientific
investigations: (1) Atmospheric Signatures and (2) Atmospheric State.
While the Atmospheric Signatures investigation requires knowledge of
atmospheric state, the Atmospheric State investigation itself is a
uniquely important investigation for the Mars Exploration Program. In
the predecessor MSO SAG-1 report, Atmospheric Signatures and Atmospheric
State were referred to as Lower Atmosphere Composition and Circulation
and were adopted, along with Aeronomy, as the foci of the mission.

### Atmospheric Signatures

#### Background

The Atmospheric Signatures investigation is aligned with NASA's search
for life beyond Earth, as well as understanding modern sources of
activity (volcanic, tectonic) on Mars.

The existence of subsurface habitable domains on Mars is suggested by
several observations. Some geomorphic evidence indicates that Mars has
been volcanically active in its recent past; there are volcanic craters
that may have been formed 1 million years ago. While ongoing extrusive
volcanism does not occur today, there is no conclusive evidence that
intrusive volcanism does not exist in the present epoch. In the frozen
Martian subsurface, geothermal systems resulting from intrusive
volcanism would likely be habitable locales. There is evidence for
shallow groundwater in the recent past and perhaps today. Indeed the
images indicating recent gully activity have been interpreted as being
the result of a transient flow of liquid water.

As on Earth, a wet subsurface environment can provide chemical gradients
that can power biological activity. The terrestrial experience shows
that extremophile life forms inhabit almost any environmental niche
where even minimally supportive conditions exist. Therefore, if life
ever existed on Mars in the past, life could still be present today if
subsurface habitable domains existed throughout the course of Mars
history.

Both geological processes and biological activity introduce
disequilibrium into the environment, including the production of gases
that could be injected into the atmosphere. It has long been suggested
that the most effective first approach for detecting the presence of
extant geological or biological activity would be to perform a survey of
atmospheric composition seeking evidence for disequilibrium chemical
constituents. However, it would be important to understand which
atmospheric constituents in very low abundance (so-called "trace
species") are simply due to the background abiogenic photochemistry
acting upon the major atmospheric species and which could not be formed
in the atmosphere and must necessarily be introduced by a
non-atmospheric process, be it endogenic or exogenic. These chemical
compounds of non-atmospheric origin can be signatures ("atmospheric
signatures") of active geological and biological processes that are
difficult to detect otherwise. Indeed, the search for atmospheric
signatures on extraterrestrial planets is the keystone of NASA's
Navigator Program objective seeking evidence of life elsewhere in the
galaxy.

Several geological processes can result in volatiles being introduced to
the atmosphere, including direct degassing from magma rising from the
subsurface storage regions through the crust, magma degassing into
shallow hydrothermal systems, and interaction of rocks with hydrothermal
solutions or ground waters. The molecular composition of released gases
likely differs from that on Earth and will depend on several variables,
including temperature of equilibration, pressure of degassing, and
oxidation state. High temperature promotes CO, and to a lesser extent
H~2~, whereas at low temperature, H~2~S, S~2~, and H~2~O is preferred.
Low temperatures also favor CH~4~ and NH~3~---in fact, these species are
likely to be negligible in volatiles directly released from magmas but
could be abundant in volatiles released from hydrothermal systems or via
lower temperature water-rock reactions. Although water is present as a
low-level background gas, local enhancements in water may provide an
additional signature of subsurface geothermal activity.

Terrestrial microorganisms produce a wide variety of gases as products
of both energy-yielding oxidation-reduction (redox) reactions and
synthesis and decomposition of organic matter. For example,
hydrogen-rich compounds including CH~4~, NH~3~, H~2~S, volatile
hydrocarbons, and alkylated amines and sulfides will form during
fermentation and anaerobic respiration under strongly reducing
conditions. Nitrogen redox reactions produce nitrogen oxides (NO and
NO~2~), and N~2~O. The thermal decomposition of biogenic sedimentary
organic matter produces light hydrocarbons. Terrestrial volcanic
hydrothermal systems provide abundant sources of chemical energy that
sustain the most robust and diverse subsurface microbial populations
known. Even in the absence of active volcanism, aqueous alteration
(serpentinization) of ultramafic (Fe- and Mg-rich) volcanic rocks or
radiolytic decomposition of water can provide H~2~ to sustain subsurface
life. The oxidation of Fe^2+^, S and/or C associated with groundwater
circulation through other types of rocks also can provide energy for
microorganisms.

In the earliest discussion of the detection of life on Mars, Hitchcock &
Lovelock suggested that the presence of reduced gases, such as CH~4~, in
an oxidizing atmosphere was direct evidence of life. Since that time, as
previously discussed above, it is now understood that geological
processes also introduce disequilibrium into the environment and
geothermal activity can inject such gases into the atmosphere. Thus, the
recent putative detections of Martian atmospheric CH~4~, have stimulated
numerous hypotheses about the nature of the methane sources, their
magnitude, and locales. Efforts to identify the sources of terrestrial
methane have found that measurements of CH~4~ isotopologues do not
necessarily distinguish between possible abiogenic and biogenic sources.
However, it has been found that the abundances of other cogenerated
species, such as ethane (C~2~H~6~), relative to CH~4~ can distinguish
between a source from active biology and other potential sources; the
C~2~H~6~/CH~4~ abundance ratio is \<10^-3^ for the former, while other
sources produce nearly equivalent amounts of CH~4~ and C~2~H~6~.

The discovery of either extant geothermal or biological processes and
their source locations would have profound implications for astrobiology
and the Mars Exploration Program (MEP). The case involving active
microbiology is clear. Identifying the locations of active geothermal
processes also would be profound. Such places would be obvious targets
for future surface exploration. If these environments were found to be
supportive of life, but nevertheless lifeless, then fundamental
astrobiological concepts would be challenged. The reported observations
of methane have suggested a seasonal variability in the CH~4~ abundance
and meridional and longitudinal variability, implying that the
distribution of CH~4~ could reveal the location of its source. However,
current Martian atmospheric photochemical models indicate that its
lifetime is \~250 Mars years, which is so much longer than atmospheric
transport timescales that the expectation is that CH~4~ should be
well-mixed throughout the atmosphere. If the reported spatial
variability is true, then some atmospheric chemical processes (possibly
dust-related) have been seriously underestimated in the current models.
On the other hand, if observations with significantly higher precision
show that CH~4~ is well-mixed, then its distribution will not be a
useful guide to locations of active processes. However, many of the
cogenerated species have much shorter atmospheric lifetimes and
therefore could be tracers leading back to source zones. In addition,
atmospheric signatures of non-methanogenic active geological and/or
biological processes may directly lead to their source regions.

#### Goals

The overarching goal of the Atmospheric Signatures investigation is to
characterize the astrobiological potential of Mars. The specific
scientific approach of using atmospheric composition as a tool for this
astrobiological exploration may allow detecting subsurface zones of
interest that cannot be characterized easily otherwise.

This investigation has four specific objectives:

1\) Identify chemical constituents in the atmosphere that cannot be
formed by atmospheric photochemical processes starting with CO~2~,
H~2~O, N~2~. Besides the tentative CH~4~ detections, other chemical
signatures arising from possible active subsurface processes may be
present in the atmosphere, but specifically which is not known.

2\) Locate sources regions of detected atmospheric signatures associated
with habitability and habitance. Knowledge of a source region provides
direction for later missions. Furthermore, even if the detected
atmospheric signatures were only from active abiogenic geological
processes and thus leading to the locations of only habitable domains,
life that doesn't introduce detectable atmospheric signatures might
still exist in these places.

3\) Determine atmospheric lifetimes of signature species. Knowledge of
lifetimes is necessary for indirectly locating a source region and for
characterizing the magnitude of the source process.

4\) Determine character of process producing signature species. To the
extent possible, distinguish between abiogenic and biogenic origins. It
may be feasible to identify the existence of active biological processes
without waiting for in situ analysis or sample return.

#### Measurement Priorities

What atmospheric signatures of active processes that might be present
and at what abundances is unknown---this is both a challenge and a major
exploration opportunity. Therefore, to accomplish the Atmospheric
Signatures objectives, the measurement requirement is to sensitively
detect a diversity of signature molecules over broad temporal and
spatial scales--not only methane.

Molecules diagnostic of active geological and biogenic processes include
sulfur, nitrogen, and reduced carbon species. These gases will have very
low abundances in the Martian atmosphere. Previous detection attempts
have been basically unsuccessful; the 10 ppbv detection of CH~4~ is
considered to have large uncertainties and the actual abundance may be
much less. Much more sensitive methods, robust to false positive
detection, are required to properly constrain the flux of biogenic- or
geologically-derived gases to the Martian atmosphere.

The detection of an atmospheric constituent in extremely low abundance
is made secure only when its presence is confirmed by simultaneous
measurement of multiple spectral features. In turn, simultaneous
detection of different species can serve as important evidence for the
identity of potential source processes; cogenerated species may span
several orders of magnitude in abundance. There is generally a trade
between detection sensitivity and spatial and temporal resolution. For
the purpose of maximum understanding of signatures present in the
atmosphere and their seasonal abundance, a detection threshold of at
least a few parts per trillion for a zonal average over 5° of latitude
is necessary to significantly exceed current observations. To accurately
derive the abundance of the signature, simultaneous measurement of
temperature also is needed.

It is not known where on Mars habitable zones might exist, and where
such zones might harbor active biological processes. As a result, the
search for atmospheric signatures must be global and must be performed
from orbit. While long-lived species will be widely distributed, many
trace signature molecules have short chemical lifetimes and,
consequently, will be detectable only near their sources. These sources
will generate plumes, the dynamics of which suggest spatial scales of a
few tens of kilometers to hundreds of kilometers. However, actual source
vents (as on Earth) are likely to occur at scales from 10's of meters to
\~ 1 km. The detection of such plumes, therefore, requires sampling of
the full Martian surface with individual measurements having a
resolution of better than 10^4^ km^2^ and a sensitivity at least \~1
ppbv, and preferably tens of pptv.

To tie an observed plume of chemicals to its surface source in an
optimal fashion, both measurements that resolve the plume structure and
knowledge of the wind field are needed. The latter requires knowledge of
the atmospheric state---both temperature fields and the distribution of
aerosols---on a global scale with a vertical resolution of \<1 scale
height. Observation of a detectable signature gas with an appropriate
lifetime (e.g., SO~2~), can be used to identify interesting source
regions, particularly in conjunction with transport modeling. Direct
observations of wind with current technologies are inadequate to track
species back to localized sources, but they provide the validation
needed to have confidence in using circulation models to track the
signature species back to its source region.

Knowledge of the atmospheric lifetime of a signature species is required
to estimate the flux emanating from the surface from observations of an
atmospheric plume and to facilitate application of inverse modeling
techniques for source location. This requires an understanding of the
background atmospheric chemistry, which will be improved by observations
of the vertical distribution of composition, temperature, and dust (at
1/2 scale height resolution). In addition, observations are required
under all atmospheric conditions, in particular over the range of dust
loading, to assess the potential impact of heterogeneous chemistry,
including electrification-related processes; the requisite measurements
of species and temperature distribution must be unaffected by the degree
of atmospheric dust content.

Besides episodic events, both climatic and biological phenomena may
introduce a seasonal signal into the atmospheric composition. Low
volatility molecular species may be depleted as ice caps form and
reappear as they sublime. When the latter occurs, resulting atmospheric
concentrations may be particularly elevated. As on Earth, any biosphere
may introduce a distinct atmospheric seasonal cycle. Therefore, it is
necessary to monitor the atmosphere over a Martian year over a broad
latitude range and with observations at every latitude at least once per
season to optimize detection of seasonal variability and more frequently
to optimize detection of episodic events.

### Atmospheric State: Orbital Science

#### Background

Atmospheric state refers to the description of atmospheric thermal
structure, pressure, winds, energy balance at the surface (albedo and
thermal inertia), the distributions of atmospheric aerosols (dust and
ice) and volatiles (water vapor and carbon dioxide), including their
partitioning between the atmosphere and surface, all as a function of
space and time. Of particular interest are the variation of atmospheric
structure and composition on time scales ranging from day-to-day, with
season, and from year-to-year. These reveal the processes controlling
the present atmospheric circulation and climate and provide insight into
climate change, including that driven by cyclic variations in
distributed sunlight as affected by orbital and obliquity changes.

In the present thin, dynamically and radiatively active Martian
atmosphere, the strongest climatological signals are the seasonal and
daily cycles, followed by the interannual variations driven by changes
in the volatile reservoirs, such as the residual polar ice caps, and in
the redistribution of dust, the latter being most dramatic in the
episodic occurrence of great dust storms in some Mars years, but not
others. The establishment of a multi-year climatology has been a major
success of the modern exploration of Mars, with seasonal coverage of the
global distributions of temperature, dust, water vapor, carbon dioxide
and surface albedo spanning more than 3 Mars years, principally by the
Mars Global Surveyor and now continuing with Mars Express and the Mars
Reconnaissance Orbiter. The Mars Science Orbiter (MSO) provides a unique
opportunity to extend and to build upon that climatological record.

This climatological record and the processes that it captures have
been---and will continue to be---exploited in two ways. First, it
provides direct evidence of the key climate processes and provides the
data needed to validate our numerical simulations of the Martian
climate. Thanks to key physical similarities between Earth and Mars
(shallow atmospheres driven by sunlight on a rapidly rotating planet),
numerical models developed to understand the Earth's weather and climate
have been adaptable to Mars and form a key part of our understanding of
how the climate system works. Second, these numerical climate models
have provided the means to simulate processes and phenomena, which
cannot today be observed directly, at least at the necessary spatial
scales and temporal frequencies. In addition to providing scientific
insight, these simulations are extensively used in the design and
implementation of critical mission phases such as aerobraking,
entry-descent-and-landing (EDL), and surface operations. Thus, a major
use of atmospheric state data is to validate that the simulations are
accurate in describing the observable environment, increasing our
confidence that they are representative of the unobserved environment.

#### Goals

The two goals for MSO with regard to the atmospheric state are: 1)
Extend the present climatology to characterize interannual variability
and long-term trends of the atmospheric state, circulation, and cycles
of dust, water, and carbon dioxide; and 2) Provide new observations that
constrain and validate models of atmospheric dynamics and state. Both
these goals require extended and frequent global coverage over at least
one---and preferably multiple---Mars years.

#### Measurement Priorities -- 1: Extend the Climatology

Extension of the present climatology requires daily, globally
representative measurements of atmospheric phenomena (hazes, clouds,
storms, etc.), of surface albedo and compositional changes (dust and
ice), and of atmospheric thermal structure over several Mars years.
Column measurements of dust opacity and water abundance are essential,
and vertical profiles with better than one-scale-height resolution over
the appropriate altitude ranges are highly desired (see the Atmospheric
State -- Orbital Science Table).

#### Measurement Priorities -- 2: New observations for model validation

The first critical need is the observation of winds day-to-day over the
globe with some vertical resolution. It is unlikely that existing
technology can provide the high spatial resolution and precision needed
to use winds directly in analyses of energy exchange and transport or in
simulations of flight dynamics and of surface operations. However, it
should be possible within the MSO resource envelope to make wind
measurements (say to a precision of 10 m/s over an atmospheric scale
height \~ 10 km) that can adequately test model simulations of
atmospheric transport and climate change.

A second critical need is the ability to cleanly describe both the
atmospheric heating (and thus suspended dust) that drives the
circulation and the atmospheric response (e.g., temperature and water
vapor distributions). Past measurements of temperature, dust and water
may have been biased by the difficulty of cleanly separating the
retrieved quantities using measurements ranging in the ultraviolet to
thermal IR part of the spectrum. The requirement is to measure
temperature and water vapor independent of dust conditions; a different
measurement approach is then needed to characterize the dust itself.

A major benefit of temperature and water vapor observations that are not
compromised by the presence of dust is that these fields can be
retrieved within the lowest scale height of the atmospheric regardless
of the dust loading. Half-scale height vertical resolution can extend
the retrievals to within a few kilometers (\< 5) of the surface,
revealing new features of storms and surface-atmosphere exchange
processes.

#### Synergies

With the measurements described above and with the improved
transport/climate models that will result from them, it should be
possible to better describe surface-atmospheric interactions (dust
lifting, storm generation, volatile sublimation/condensation) key to
many climate processes. It should also be possible to do the inverse
problem of tracing spatially varying minor atmospheric constituents (or
trace gases, water being one) to localized source areas. The ability to
do this---or alternatively, the uncertainty of the source region
size---depends strongly on the nature of the source and the lifetime of
the traced gas. Of particular interest would be to capture the trace gas
evolution in different seasons and under different (dust) storm
conditions. Multi-year coverage increases the probability that a
representative suite of dust activity will be captured.

### Atmospheric State: Landed Science

#### Background

Detailed meteorological measurements have been obtained from only 3
locations on Mars; the two Viking Landers and Pathfinder (which was very
similar meteorologically to Viking I). The MER rovers did not carry a
traditional meteorology package and the Phoenix lander has a relatively
simple meteorology package. Because of this paucity of observations,
there still remain many questions about the processes that occur at the
interface between the surface and atmosphere on Mars. There are also
important engineering considerations for the safe delivery and operation
of spacecraft to the Martian surface that give more incentive to observe
the atmosphere from the surface.

#### Goals

The first and most basic question that one would address with a landed
meteorology package at Mars would be one of better understanding how
representative the previous 3 observation locations are to Mars in
general. Just as on Earth, weather is an inherently local phenomenon, so
there is always advantage in characterizing its behavior under
meteorologically distinct settings. To satisfy this goal, even a
relatively basic, but complete meteorology package could suffice.

Martian meteorology is punctuated by dramatic dust storms and dust
devils, both of which may have significant consequences for the climate,
weather and even perhaps chemical makeup of the atmosphere. For Mars, it
is important for the standard meteorological observations to not only
characterize the typical conditions, but also those of the extreme
events. This is best accomplished by sending capable instrumentation and
adapting its observational behavior during these infrequent events to
best capture their special properties.

The types of questions that are now of interest at Mars extend beyond
these simple meteorological quantities. In particular, the questions
more directly address the interaction between surface and atmosphere, in
terms of transports of mass, momentum and heat between the two
reservoirs. This drives us to more sophisticated observations than the
simple, classic meteorology packages that have been sent to Mars. These
"next-generation" measurements address the boundary layer on Mars, and
the processes that control the mixing of mass, heat and momentum through
this layer connecting surface and atmosphere. On Earth, this type of
observation is typically done by directly measuring the eddy fluxes
through the boundary layer. This is now becoming feasible for Mars as
well, and is required to advance our understanding of Mars.

Another advantage of obtaining these 'next-generation' boundary layer
measurements from the surface of Mars is that it will allow us to more
fully validate the many types of atmospheric models in use for Mars.
Because our modeling capabilities have advanced dramatically since even
the time of Pathfinder, we are now in a position where the models are
significantly underconstrained by the available data. More sophisticated
observations are needed that can place more stringent constraints on the
models (ranging from simple 1-D models to large eddy simulations,
mesoscale models and global circulation models), and should be done to
allow maturation of these models and our general understanding of the
interaction of Mars surface and atmosphere.

In addition to understanding the fundamental boundary layer processes
described above, there is also great desire to better understand the
processes controlling the stability of water in all phases as it is
transported between surface and atmosphere. On Earth, this is typically
done with a "closure experiment", where the factors forcing the
transport and stability of water are measured, as well as the actual
distribution and transport of water itself. Again, these observations
are now becoming feasible for Mars. This approach, where the processes
that control water stability on Mars become better understood, will
allow us to extrapolate to other locales on Mars, as well as other
epochs to predict the behavior of water at those times and places.

Finally, the possible significance of dust electrochemistry on the
lifetime of biosignatures has recently been recognized. While
theoretical work on this problem is moving ahead, direct observations of
dust electrification effects would place this work on much stronger
footing. Instrumentation to measure this is now lightweight and simple,
and should be considered part of a nominal meteorological station for
Mars.

#### Measurement Priorities

Pressure and temperature constitute the most basic meteorological
observations that can be made and should be part of any landed
meteorological package. To be of value, these measurements should be
accurate to 0.02% (pressure) and \~1K (temperature). Adding winds to the
measurement dramatically increases the constraints that the data set
provides to validating models. If the winds are measured with full 3-D
resolution, and with adequate sensitivity (5cm/s) and temporal
resolution (\~10 Hz), then direct eddy fluxes of momentum can be
obtained as well. If the temperature is also measured with a fast
response instrument (0.5K @ 10Hz), then heat fluxes can also be directly
measured. Similarly, if water vapor is measured with enough speed and
precision (0.1ppmv @ \~10Hz) then water vapor fluxes can also be
directly measured. To complete the "closure experiment" on water
stability, the measurement complement should include surface temperature
as well as atmospheric backradiation in the form of a boundary layer
temperature profiler akin to the Mini-TES instrument on the MER rovers
(sensing 0-5km with an accuracy of \~1K). Incoming and reflected solar
flux should be measured to 3-5% of the total solar flux at Mars. The
dust opacity should also be measured to within 5%. Finally, to achieve
the dust electrification measurements, one component of the E-field
(preferably vertical) should be measured at 20 Hz, triggered in the
presence of passing dust. The sensitivities should be between 0.1V/m and
100 kV/m.

#### Synergies

Landed observations complement the orbital atmospheric observations in
several ways. First, the unique perspective of upward sensing
column-averaged retrievals of water vapor, ice and dust can be more
accurate than orbital estimates of the same parameters because the
background is cold sky rather than warm ground. Overflights allow
calibration of these quantities between the two platforms. Surface
pressure changes with time are indicative of the scale of weather
systems in the vicinity of the lander, which can be compared with
orbital estimates of weather system structures. Weather phenomena are
best observed at the surface where they are strongest, but often
difficult to fully resolve from orbit. Combining simultaneous detailed
surface observations and global-coverage orbital observations
strengthens the depth of understanding available from both data sets.
The boundary layer processes that feed into the thermal, dust and
volatile transports making climate a key question on Mars are only well
observed from the surface. Combining global observations with local
observations of forcing and response allows for more confident
extrapolation to other locations and epochs.

Such a Next-Generation meteorology package as described here is also a
pilot study for future missions that would use trace gas horizontal
fluxes to 'hunt' sources of biosignatures by following plumes upstream
to their source. In order to establish appropriate constraints on the
response time of biosignature detectors, we need a better understanding
of the turbulent spectrum in the Martian boundary layer. Only by sending
capable instruments to Mars can we obtain this knowledge.

Electrical field measurements directly impact our understanding of the
lifetime of trace gas species. These effects are only available at the
ground on Mars. Combining orbital trace gas observations with surface in
situ electrical field/dust measurements can expand our understanding of
trace gas interactions with dust.

![](media/image1.pct){width="9.85in" height="7.518055555555556in"}

![](media/image2.pct){width="9.990972222222222in"
height="7.038888888888889in"}

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height="6.615972222222222in"}

## Polar Processes and Modern Climate

### Background

The modern Martian record of volatile reservoirs and their dynamics is
uniquely manifested in the polar regions. The NRC Decadal Survey (2003)
has suggested that a more complete understanding of the sources and
sinks of major volatiles systems within the Solar System is a
potentially paradigm-shifting priority across the next decade of
planetary exploration. This overarching objective ties the modern record
of climate to the migration pathways within the accessible Mars "system"
of primary volatile species, including CO~2~ and H~2~O. It also serves
as the context within which to document and quantify climate variability
and the modern history of water in three dimensions, which links it
directly to MEPAG priorities within Geology and Geophysics. Given the
role of volatile reservoirs in the broad theme of "habitability",
pursuit of polar processes and climatology is of significant importance
in the science of Mars.

The most likely location of a preserved record of recent Mars climate
history is contained within the north and south polar deposits and
circumpolar materials. The polar layered deposits (PLD) and residual ice
caps may reflect the last few hundred thousand to few million years,
while terrain softening, periglacial features, and glacial deposits at
mid to equatorial latitudes reflect recent high obliquity cycles within
the last few million years. Dune and mantling deposits around the
northern PLD span the entire Amazonian period, \~ 3Ga to the present,
and multiple sequences of deposition and erosion are recorded.
Understanding the interaction between the current climate and current
residual ice caps will act as a \'Rosetta stone\' which we can use to
interpret the layered deposits in terms of the previous climates which
formed them.

Recently, five high level questions with regard to polar processes have
emerged from the polar community and were considered and revised by the
SAG-2. These are:

1)  What are the mass & energy budgets of both seasonal and residual
    volatile deposits, and what processes control these budgets on
    seasonal and longer timescales?

2)  How do volatiles and dust exchange between polar and non-polar
    reservoirs? How has this exchange affected the past and present
    distribution of surface and subsurface ice?

3)  What are the physical characteristics of the polar deposits and how
    are the different geologic units within, beneath, and surrounding
    the PLD related?

4)  What chronology, compositional variability, and record of climatic
    change are expressed in the stratigraphy of the PLD?

5)  How old are the polar-layered deposits? And what are their glacial,
    fluvial, depositional and erosional histories?

We briefly summarize current polar and climate processes from seasonal
to longer timeframes and consider what critical new measurements MSO can
make to contribute to these questions.

#### Seasonal polar ice caps

The current Mars climate is driven by the advance and retreat of the
seasonal polar caps, with approximately 25% of the atmosphere condensing
into the caps during autumn and winter and sublimating back into the
atmosphere in the spring. This annual process is controlled by the net
energy balance of absorbed insolation and thermal radiative losses to
space. Net energy can be stored in the ice rich regolith, laterally
transported by the atmosphere, or converted to/from the latent heat of
fusion for CO~2~ ice. The lateral transport of heat in the atmosphere
associated with seasonal cap formation and ablation is not well
constrained and could be quite large, depending on the location and
season. The atmospheric transport contribution may be the same order of
magnitude as the heat storage contribution from an icy regolith.

The edge of the advancing cap is typically 10 degrees of latitude
equator-ward of the edge of polar night. This means that the dominant
processes that control the condensation of the cap occur within the
polar night, a region that is invisible to passive visible and near
infrared cameras and spectrometers. Early spacecraft thermal
observations of the seasonal caps revealed brightness temperatures
significantly lower than the expected kinetic temperature for CO~2~ ice
in equilibrium with a CO~2~ atmosphere. These cold areas or spots were
typically a few hundred kilometers in diameter, with 20 µm brightness
temperatures as low as 130K and typical lifetime of a few days. The cold
spots may be freshly deposited CO~2~ snow, CO~2~ condensates high in the
atmosphere (clouds), or "dry ice blizzards". While the "dry ice
blizzards" are short-lived, the snow that remains can be observed as
cold spots for up to several weeks, thus affecting the long-term energy
balance. MOLA, TES, and radio science experiments agree that the polar
night of both polar caps have significant CO~2~ cloud cover, which also
affects cap condensation. The exact effects of these processes on the
energy balance are still poorly constrained and additional observations
are needed.

The distribution of seasonal CO~2~ ice provides information about the
interaction between the atmosphere, topography, and surface properties.
The density of the CO~2~ ice constrains several important polar
processes, including deposition mechanisms and densification.
Measurements of density are more uncertain than mass, owing to current
uncertainties in linear thickness measurements and comparisons between
regionally averaged frost values and local measurements provided by
MOLA. Current estimates of seasonal CO~2~ ice densities vary from 500
kg/m^3^ to 1200 kg/m^3^ depending on location and technique used.

Critical new measurements to be made regarding the seasonal caps include
the polar night energy balance, density of the seasonal cap, and
volatile and dust transport in/out of the Polar Regions. Energy balance
is addressed through surface and atmospheric temperature and albedo
measurements. An active laser system can be used to determine cloud
condensation altitudes coupled with concurrent thermal measurements
during the polar night. Thermal spectroscopy and bolometry provide
temperature as a function of altitude in the condensing atmosphere as
well. Density of the seasonal cap is determined by precise measurement
of cap volume coupled with mass estimates of CO~2~ in exchange with the
atmosphere. Volatile and dust transport are monitored with visible
imagery and through compositional mapping.

#### Residual polar ice caps

The southern residual CO~2~ cap is finely layered and typically a few
tens of meters thick. As has recently been discovered by THEMIS and
OMEGA this CO~2~ veneer is underlain by water ice. Changes in the
appearance of the residual ice between the Mariner 9 and Viking missions
and modeling of "swiss cheese" formation via sublimation suggest this
upper CO~2~ layer could be less than a few thousand Martian years old.
Observations of expanding pits have prompted suggestions that this
reservoir of CO~2~ ice is rapidly shrinking implying current climate
change. The highly inclined walls of these pits are expanding at rates
of up to 5m/year; however, without understanding the mass balance of the
intervening flat surfaces it is impossible to discern whether the
residual cap as a whole is gaining or losing CO~2~ ice, a gap in our
current understanding. This small reservoir of solid CO~2~ buffers the
atmospheric pressure and so, in part, controls the current climate.
CO~2~ ice is considerably more volatile than water ice, and the southern
residual cap responds sensitively to any change in climatic conditions;
thus, understanding the mass balance of this deposit not only informs us
about the climate of today but also that of the recent past and near
future.

In the north, the problem is somewhat different. The residual water ice
cap is lower in albedo, compared with the south, implying both older,
coarser ice and more dirt contamination. The finest layers observed are
near the resolution limit of currently available imagery. OMEGA data
have recently indicated that there is a strong component of water ice in
the seasonal frost and that this seasonally deposited water frost is
sublimated after the CO~2~ and by mid-summer exposes old, large-grained
ice to ablation. Recent studies using TES have shown highly variable
albedo and frost migration patterns during the northern summer. Frost
migration has both a large-scale pattern that repeats annually and
subtle small-scale features that are highly variable from year to year.
Frost mobility and seasonally sustained fine-grained ice may represent a
complicated spatial pattern of accumulation and erosion occurring
throughout the residual water ice cap. Constraining the current
deposition and erosion rates is needed to provide a powerful boundary
condition on the availability of water vapor and also link the observed
layers to annual or longer climate cycles.

Critical new measurements to be made with regard to the compositionally
distinct residual ice caps include: residual cap volume, mass balance,
time variability of albedo and composition, slopes related to flow and
relaxation, and small changes in volume with time. Multi-temporal
measurements of the cm-scale topography of both the seasonal and
residual polar caps can now be achieved via orbital multibeam laser
altimetry. This will address both volume and mass exchange with time as
well as a high-resolution assessment of slopes. Albedo and composition
need to be monitored with better time resolution than MRO, observing the
entire cap within a few degrees of Ls. Such monitoring can occur at
selected optical, near-infrared and thermal infrared wavelengths, chosen
specifically to distinguish water and CO~2~ ices as well as non-ice
components.

#### Polar Layered Deposits (PLD)

Since the layers within the PLD likely contain the best-preserved record
on the planet of recent Martian climate history, understanding their
stratigraphy is important. While rough stratigraphic correlations can be
obtained through the use of MOC images tied with MOLA altimetry, MOLA
data do not provide accurate enough estimates of layer elevation. Higher
spatial resolution/vertical accuracy elevation data are needed which can
then be tied more accurately with existing imaging data sets. Even
existing imaging data sets are insufficient to fully characterize PLD
stratigraphy. Previous experience demonstrates that only a select few of
the available images may be suitable for layer correlation and hence,
while past image data sets will certainly carry us closer towards a
fuller characterization of PLD stratigraphy and are a necessary first
step, more high resolution image coverage is necessary for a complete
understanding. Indeed, cm-resolution topographic correlation of PLD
layers across the full extent of the polar cap system may allow an
improved assessment of the history of this important system, and
facilitate assessment of individual layer volumes (and hence deposition
rates).

The records in both PLD have been modified over their history by several
processes. The significance of ice flow in modifying the overall
internal layer structure of at least the NPLD is likely to be
negligible, but understanding its impact on small-scale structure (such
as localized deformation) is necessary to allow this record to be fully
interpreted. Flow velocities are also interpreted to be higher at
marginal scarps and other steep slopes, possibly competing with
sublimation in forming the overall shape of both polar domes. Crater
morphologies on the layered deposits may also be the result of viscous
relaxation of the target material, and relaxation may remove craters,
falsely decreasing the apparent surface age derived from crater
counting. Radar sounding of layer shapes around craters will reveal the
extent to which they have viscously relaxed. A detailed surface
topography model (with extremely high vertical accuracy) will also be
needed to accurately model crater shapes. PLD shapes derived from
multi-beam laser altimeter data more accurate than those from MOLA will
also allow us to better constrain flow models and to better test for the
effects of flow on steep margin scarps.

The surface of the south polar layered deposits is mantled with a
cohesive but low thermal inertia material, which is likely to be a
sublimation lag deposit. The thickness of this mantle is unknown and may
vary considerably throughout the region. However, locations where it is
only millimeters thick (where the thermal signature of the underlying
water ice shows through) have recently been discovered. Younger
ice/dust/frost deposits also appear to mantle the layers exposed in the
NPLD troughs, masking their inherent albedo. Such thin lag deposits can
impact energy balance due to the different thermal inertia of the
underlying ice.

#### Mid-latitude Glacial and Periglacial deposits

Meters-thick ice-rich deposits, in latitudinally dependent states of
continuity or degradation, drape pre-existing topography poleward of
30°. The presence of these youthful deposits can be explained by
redistribution of polar volatiles by orbitally driven climate change
over the past 3-5 million years. The suite of ice related features are
the most well preserved record of Mars climate processes affecting the
mid-high latitudes, and it is essential to understand this record to
constrain how volatiles are cycled among surface reservoirs. A more
complete understanding will have important implications for assessing
recent habitability and defining resource availability. To better
constrain the volumes of ice contained within the mantle, we need
accurate measurements of its thickness, best provided by high vertical
accuracy topography. Furthermore, there is abundant evidence for glacial
and periglacial deposits and features in mid latitude and equatorial
regions (e.g. tropical mountain glaciers) pointing to even more vigorous
redistribution and cycling of volatiles in the earlier Amazonian. To
better understand the amounts of ice implied by these features and their
evolution through time, we need to know the volumes of the glacial
deposits and their slopes as measured from high spatial resolution/high
vertical accuracy topographic data. Such measurements will allow for
better-constrained modeling of glacier shape and how that shape relates
to climate. Imaging radar data would create access to the morphological
aspects of non-polar ice features that are often covered by dust.

### Priority Goals and Measurements

The SAG-2 considered areas where MSO observations of the polar, glacial
and periglacial terrains would enable major advances in the
understanding of the current and previous Martian climate. In the
context of recent discoveries and outstanding issues describe previously
a series of new priority measurements were defined. These are:

1)  Thickness, volume and slopes of seasonal, residual, PLD and lower
    latitude glacial deposits.

2)  Changes in volume of volatile deposits as a function of location and
    season.

3)  Density of seasonal ice deposits as a function of location and
    season.

4)  Mass and energy balance through albedo, temperature, composition,
    topography, atmospheric transport, and polar night processes. High
    time resolution observation in variation of these properties.

5)  Stratigraphy of PLD and residual ice, particularly the upper few
    10's of meters not accessible to MARSIS and SHARAD.

Extremely high vertical resolution topographic data (i.e., few cm) can
be used to map both seasonal and permanent deposits in three dimensions
and to correlate them across wide regions at sub-meter vertical scales.
High-resolution imagery will help us to interpret the stratigraphic
information we compile in terms of previous climate regimes. SAR (and
related nadir-SAR "sounding") can be used to \'see through\' lag
deposits, which currently covers much of the PLD and also to
characterize individual layers' scattering properties. In order to more
definitively tie the preserved layer record to past climate changes, an
understanding of the current residual cap energy balance (at both poles)
and its relationship to current atmospheric dynamics and orbital
parameters is necessary. No other existing (MEX, MRO, Mars Aeronomy
Orbiter) orbital remote sensing approach can provide this unique
information. Proposed priority measurements could profoundly impact the
state-of-knowledge in this area. As such, the proposed measurements
would tie non-polar latitude evidence of polar processes (tropical
mountain glaciers, periglacial landscapes, mantling deposits) to global
evolution of the planet within differing climate regimes. This could
relate the history of atmospheric density to climate variability and
thereby improve GCM fidelity.

#### Topography and deposit volume

Increased spatial resolution topographic measurements are expected to
provide constraints with regard to the seasonal and residual CO~2~ ice,
accurate volumetric measurements of the PLD and residual caps, and
characteristics of mid- to high-latitude glacial and periglacial mantled
deposits. Quantifying the seasonal cycle of CO~2~ frost in 3 dimensions
will facilitate the identification of the timing of the onset of erosion
between seasonal and residual ice in the south. High-resolution
measurements of elevation changes (or lack thereof) will permit
determination of the extent and direction of changes in the current
atmospheric pressure and, by extension, the climate. High-resolution
topography can constrain the seasonal cap volume and by measuring mass
exchange with the atmosphere constrain the cap density. Higher
resolution topography will identify unusually high surface slopes,
providing critical information for flow and relaxation models of these
features. As the PLD are the expected source of mid to high latitude
deposits, concurrent measurement of the volume of the PLD and of these
glacial and periglacial features will provide constraints on the amount
of water exchanged at different obliquity periods.

Multi-temporal measurements of the cm-scale topography can now be
achieved via orbital multi-beam laser altimetry. Monthly gridded
measurements of the geodetic topography of the polar regions can now be
achieved with 3-5 cm (RMS) vertical accuracy at horizontal scales as
fine as 100m. By measuring the monthly topography of the polar cap
systems on Mars high-precision measurements of the differential volume
of volatiles can be made, at 100 times the resolution demonstrated by
MOLA. Such measurements can be integrated into volume estimates and the
volume change on a seasonal basis can then be quantified and compared
against MGS-era estimates. All of these measurements fully resolve the
spatial properties of the polar cap system at \~ 100m horizontal scales,
and as such can be coupled to energy balance measurements at similar
horizontal and spatial scales. A simple Radio Science Experiment (RSE)
employing an Ultra-Stable-Oscillator (USO), as on MGS, can be used to
measure the mass of CO~2~ in the atmosphere. Using these mass and volume
measurements density of the volatile deposits can be estimated.
Continuation of such measurements across the polar night and independent
of the polar hood and other cloud-cover phenomena will produce a highly
time-resolved sample of the mass exchange dynamics of the polar and
atmospheric volatile reservoirs.

High-resolution multibeam laser altimeter measurements of PLD, glacial
and periglacial deposits can resolve their three-dimensional character,
allowing their volumes (and masses) to be assessed. New information on
layer geometries and volumes across the entire expanse of the deposits
can be made. This will provide the context within which continuing
sub-meter imaging can be used to develop quantitative models of the
salient processes responsible for PLD formation and destruction. In
addition, the geodetic quality of the measurements will allow detailed
estimation of individual layer or layer bundle volumes, even in cases
where portions of the layers are buried. Such volumetric measurements
can then be tied to mass flux estimates that link the PLD to
mid-latitude glacial features and ultimately to processes related to
climate variability.

The layer volume measurements can be amplified by including observations
of the shallow layering structure of the polar caps by means of various
active microwave methodologies, including long-wavelength
multipolarization SAR (i.e., at L or P-bands), or via high-bandwidth
nadir SAR observations processed using Delay-Doppler methods to
facilitate shallow layer "sounding". These methods could provide
sub-meter layer imaging or ranging observations at scales as fine as
100m across the polar cap systems on a seasonal basis. Such measurements
would bridge the gap between VHF sounding radar observations from MARSIS
and SHARAD, which cannot resolve the fine-scale (i.e., sub-meter)
vertical layering structure within the polar caps within tens of meters
of the surface.

#### Mass and Energy Balance

Early estimates of energy balance assumed that the regolith had a
sufficiently low thermal inertia so that heat storage of the regolith
could be neglected. Most energy balance studies have followed this
example. The discovery of the presence of high concentrations of
near-surface H~2~O ice at high latitudes has brought into question the
assumption that the regolith can be ignored in energy balance studies.
In fact, the energy balance, and thus the accumulation of seasonal
CO~2~, can be greatly affected by the presence of surface and
near-surface ice. H~2~O ice stores a significant amount of heat during
the summer and then releases this heat during the fall, delaying the
formation of the seasonal CO~2~ and reducing the net accumulation. Most
energy studies have also been 1-dimensional models, and therefore
implicitly ignore atmospheric transport of heat. GCMs, which include
atmospheric transfer of heat, have yet to fully implement effects from
high thermal inertia regolith in the polar regions. A space-borne
platform, with a suite of instruments that measure nearly all aspects of
the energy balance in the polar regions can be used to constrain
atmospheric transport and provides an independent validation of Mars
GCMs.

A detailed analysis of the polar energy balance will provide a better
description of the stratigraphy of the near surface regolith to include
thermal inertia, water ice content, and depths to the ice table. Heat
transport will be inferred from the residuals of the polar energy
balance and compared to GCMs. Atmospheric dynamics and transport plays a
significant role in the formation and dissipation of the polar caps,
perhaps even being the cause of both the SPRC offset and the location of
the Cryptic region. Determination of the energy balance is achieved
through thermal and vis/NIR observations for albedo and temperature with
time. Thermal and vis/NIR observations will enable our ability to
constrain the local column abundance of CO~2~, the composition,
stratigraphy and thermal properties of the regolith, the solar energy
absorbed by the surface, and the thermal energy lost to space. Thermal
inertia is derived from seasonal temperature curves and coupled with
estimates from GRS can constrain the depth to the water ice. The mass
balance between the atmosphere and the polar caps can be assessed as
described in the previous section using high-resolution topography and
radio science estimates of mass. Crucial to the energy absorption is
identification of water content in seasonal frost and dust content in
residual ices. This measurement is achieved through high temporal
sampling at selected near-infrared wavelengths.

#### Stratigraphy and Mantling

A key goal will be to correlate the layers within both PLD and to
discern the relationship between stratigraphy and the climatic record.
This will be accomplished through high-resolution imagery and altimetry,
compositional mapping and determination of near-surface layers and
mantle deposit thickness using SAR imaging and sounding techniques.

Correlating exposures of individual, thin layers and packages of layers
visible in high resolution imagery will facilitate mapping each layer in
three dimensions, as has been performed at lower resolution using MOC,
MOLA, and THEMIS data in both the north and south. This can be extended
by an order of magnitude using the combination of sub-meter imaging
together with cm-precision multi-beam laser altimetry. Similar
techniques can be used to more accurately and much more thoroughly
correlate better-defined layers using additional data. HiRISE is capable
of resolving the thinnest layers visible from orbit, but the coverage of
the layers will likely not be enough to definitively characterize polar
stratigraphy. Rather, HiRISE will provide a sample, which may or may not
be representative, especially given localized controls on deposition
(microclimates). Thus, more high-resolution image coverage by MSO will
be necessary for completing layer correlation studies. High spatial
resolution topographic data is needed to link the layers observed in
images with their elevations so that one can create a 3D map of layer
stratigraphy. MOLA data is insufficient for the task, and only just
barely useable in connection with MOC images. While HiRISE may provide
some stereo coverage from which high resolution DTMs can be produced,
such coverage will be sparse, and a comprehensive stratigraphic study of
a region as large as the PLD cannot rely on labor-intensive stereo DTM
production alone. While SHARAD and MARSIS provide some valuable insight
into the internal structure of the PLD, they cannot resolve layers
visible in images. Higher vertical resolution radar data would be
extremely useful for tracing layers exposed in trough walls beneath the
flat, between-trough areas where layers are not exposed at the surface.

High-bandwidth SAR instruments can now be operated in creative new
modes, thereby facilitating measurement of sub-surface layering at
sub-meter vertical scales. Nadir SAR sounding using high-bandwidth
systems and delay-Doppler processing methods can now be used to resolve
layers only 70cm thick within the uppermost tens of meters of ice
deposits. Based on existing, low-resolution MARSIS and SHARAD results,
these techniques can be expected to penetrate 10's of meters in the
Martian polar regions. This could provide spatially resolved maps of the
stacks of layers within tens of meters of the surface at scales as fine
as 100-200m (horizontally) and allow correlation of these buried layers
with exposures in troughs, reentrants and at the cap edge. In addition,
buried layer continuity can be probed across scales as wide as the
residual caps themselves. This would result in gridded datasets from
which measurement of volumes can be achieved. Such volumetric
measurements can be used to estimate layer thicknesses and shapes below
the surface. There is likely to be a density contrast between seasonal
and residual CO~2~ frost (perhaps by a factor of 2-3), so there may be a
reflection from this interface as well as the surface-atmosphere
interface that can be used to quantify the seasonal frost thickness.
Penetration of thin mantling deposits is anticipated via classical SAR
imaging methods, which can separate these deposits from the larger
fraction of the PLD. Such measurements could feed-forward to missions
that directly sample the shallow subsurface of the caps themselves.
Comparisons of the thermal, morphologic, and topographic properties of
the residual ices with those of the layers in these deposits can be used
to further constrain the details of the state and composition of this
material. In this way the climatic record in the polar layered deposits
can be completely characterized in three dimensions and at scales
appropriate for sub-regional modeling (sub-km).

**Table 6.2 Polar Goals Matrix**

![](media/image4.pct){width="8.889583333333333in"
height="7.519444444444445in"}

## Geology: Near-surface Science

### Overview

In response to the SAG-2 charter element regarding orbital geophysics,
the "geology" sub-group was tasked to develop scientific questions,
consistent with the MEPAG goals document of February 2006, and to
propose feasible instruments that can accomplish the corresponding
investigations. A second charter element focused on the major drivers
for a high resolution imaging system on MSO, particularly with regard to
landing site planning. The geology sub-group developed a number of
investigations under the broad themes of "Ancient Environments" and
"Dynamic Mars/Mars Today" (Table 6.3). These investigations address
major scientific questions, responsive to the MEPAG document and having
a high degree of feed-forward for future mission planning.

In order to provide a meaningful basis for comparison and prioritization
among the SAG-2 sub-groups, scientific investigations developed by the
geology group are directly correlated with one or more MEPAG-recommended
areas of study. Two over-arching theme areas emerged from this effort:

1.  Ancient Environments -- This theme reflects primarily the MEPAG
    interest in locating and characterizing the geologic signatures of
    conditions that may have provided habitable settings, and in
    understanding how these conditions varied with space and time.

2.  Dynamic Mars/Mars Today -- This theme reflects primarily the MEPAG
    interest in the current state and distribution of water across Mars,
    rates of change due to various processes, and the location of areas
    of remnant thermal or tectonic activity.

Within each of these areas, the sub-group developed a number of
scientific investigations to address questions that remain after recent
or ongoing orbital and landed missions (Table 6.3).

### Ancient Environments

Results from the Opportunity rover traverse and mineralogy maps from the
OMEGA and CRISM instruments suggest that "habitable" conditions existed
in various locales for limited periods of time. Understanding the
duration and extent of these conditions based on the geologic record is
a key MEPAG goal. Two complementary major investigations for MSO are
proposed.

The first approach emphasizes greater visible image coverage, at the
highest possible spatial resolution, of layered bedrock exposures linked
with sedimentary depositional environments. With sufficient resolution
(e.g., 5-10 cm per pixel), these observations could augment the much
more localized observations of surface rovers in revealing potentially
habitable settings. Group discussion, however, suggests that increased
coverage at the image spatial resolution consistent with current
capabilities (\~30 cm per pixel) could also address many of these
investigations. The well-exposed sedimentary deposits cover extensive
areas, while HiRISE on MRO can cover \<1% of Mars at full resolution in
the nominal mission. The alternative approach of using very high
spatial-resolution (e.g., 1-2 m per pixel) synthetic aperture radar data
was not deemed practical to satisfy the surface imaging science
requirements. At a lower priority level to the high-resolution imaging
goal is an interest in the mineralogy of layered or possible
water-formed deposits at much higher spatial resolution (e.g., a few
meters per pixel) than currently available from orbit.

The second approach emphasizes mapping of the near surface geologic
record to reveal the morphology of bedrock buried by meters of sediment,
and to thus define the extent and stratigraphy of units associated with
limited outcrops of layered or compositionally significant (e.g.,
phyllosilicates, sulfates, carbonates) materials. The near-surface
geologic record may also contain evidence of process-specific landforms
(lava flow fronts, deltaic fans) not evident from visible imaging.

For example, some sequences of the light-toned layered rocks studied by
the Opportunity rover likely formed in the presence of running water.
Whether these deposits reflect deposition in habitable environments is a
topic of ongoing discussion, but a crucial outstanding question is their
spatial extent beneath widespread mantling materials. Mapping of the
upper bedrock surface below the mantling deposits will reveal the extent
of the sedimentary rocks, and place constraints on the extent of the
aqueous environment in which they formed. In other locations, an
interpretation from OMEGA results is that there was a sequence of
climatic periods during which phyllosilicates formed early, followed by
sulfates. These indicators of ancient climate are known only from
limited outcrops where their spectral properties can be measured.
Subsurface imaging from orbit of the bedrock geomorphology will reveal
the extent and modification of materials seen in outcrops, and expand
our knowledge of the size and distribution of potentially habitable
environments.

No existing remote sensing data uniquely map the thickness of surficial
sediments across Mars, but there are studies that suggest the range of
depths. For example, the MER and MPF rovers and earlier Landers reveal
outcrops of bedrock, and small craters, that are buried by less than a
meter of fine material. Orbital images show abundant examples of
sediment-muted terrain features (i.e., small impact craters) that imply
a thickness of no more than several meters. The thicknesses are more
directly revealed at the edges of steep slopes, for example associated
with craters or troughs, but this provides spotty information.
Earth-based radar data detect rugged lava flows covered by sediments
that must be less than a meter or two thick. Finally, thermal inertia
studies show that many "dusty" areas have some component of exposed
bedrock or surface blocks, consistent with sediment thickness of tens of
cm to a few meters. Based on this evidence, 3 m is a conservative upper
estimate of mantling deposit thickness over many features of interest.

### Dynamic Mars/Mars Today

Known activity on Mars includes seasonal cycling of polar cap deposits,
longer-term changes in the residual caps, aeolian movement of fine
material, downslope debris movement, a slow accumulation of small impact
craters, and possibly discharge of water in very limited settings. These
changes can be identified in long-term imaging, and quantified through
detailed stereo mapping or other techniques. Many of the processes
observed on Mars have not been fully characterized, such as the southern
residual cap retreat, the global cratering rate (flux), aeolian sources
and sinks, and the occurrence of slope-related features that could be
formed by water. Some features of the current Martian water inventory
remain elusive, such as the detailed distribution of near-surface ground
ice partially mapped from hydrogen abundance. Other processes that may
occur, such as ground changes due to ice sublimation, tectonic motions,
or thermal uplift/subsidence, have not been constrained by any
measurement to date.

The SAG-2 sub-group developed a varied list of science investigations to
address these outstanding issues (Table 6.3). These investigations
emphasize the role of water at and near the surface by ongoing
visible-image monitoring of slopes where discharges may occur and sites
of change in the residual caps, and by seeking a detailed spatial
characterization of ground ice at high latitudes. In a more global vein,
investigations will seek evidence of modern ground motion due to
endogenic processes, measure the rate of cratering as a guide to
relative age dating of surfaces on Mars, and characterize the rates and
general sources and sinks for weathering processes.

Surface visible imaging at the 30 cm / pixel scale, with the capability
to acquire stereo-compatible pairs for detailed local topography,
satisfies many of the goals of targeted monitoring of surface change
(e.g., in the residual caps and gullied slopes). Wider-area image
coverage (not necessarily at visible wavelengths) at lower spatial
resolution (a few km) is also required for long-term monitoring of
larger regions. This capability is particularly important in detecting
surface changes, some of which mark recent activity such as fresh impact
craters. Once identified, high-resolution observations enable detailed
study.

The goal of characterizing possible ground movement due to ice-related,
thermal, or tectonic processes requires a method for measuring changes
at the few-cm vertical scale in datasets collected over intervals of
weeks to months, and preferably over large regions of interest. There
were concerns raised regarding the likelihood of a detectable
deformation event within the expected primary MSO mission, but the great
importance of any such detection to the development and deployment of a
surface network mission argues for making these measurements.

The current distribution of ice trapped in frozen ground at high
latitudes is a major element in understanding the inventory and movement
of water on Mars. The upper several meters of the Martian regolith at
high latitudes is predicted to contain a significant amount of water
ice. The presence of this ice was confirmed by observations of the upper
\~1 m by the Gamma Ray Spectrometer (GRS) suite on Mars Odyssey. GRS
observations indicate that ice volume fractions in the upper meter are
over 50% in the polar regions, decreasing to 10% or less near 50-60°
latitude. At mid-latitudes the ice is unstable near the surface and the
hydrogen signal in GRS data can be explained by hydrated minerals, but
ice may be present at greater depths.

The SAG-2 gave high priority to identification of thinly mantled "clean"
ice deposits. Geologic features formed by the action of ice in frozen
soil are common on Earth. Polygon patterned ground is the most
ubiquitous of these features, resulting from seasonal thermal
contraction and cracking in ice-rich soil. Polygons are observed in
abundance in the Martian high latitudes, ranging in size from 1 to 100's
of meters. Such features are an indication of current ice-rich soils or
past ice history. The GRS data, however, are of low resolution (300--600
km), so the local-scale distribution of ground ice and expected
relationship to patterned ground is yet to be confirmed. A search for
shallow, relatively "clean", subsurface ice covering areas a few hundred
meters or more in extent (frozen lakes, buried compact snow, or relic
glacial ice), based on morphologic, density, electrical, or other
diagnostic differences from ice-poor areas is needed.

### Priority Measurements 

The MSO measurements that address these investigations comprise (in
priority order):

*Surface Imaging*. Based on interest in observing sedimentary layering
and other geologic signatures of ancient climate, creating stereo
topographic maps of targeted areas, searching for modern-day change due
to ice, water, and aeolian processes, and to characterize landing site
hazards, MSO should carry an imaging system with a spatial resolution of
better than 1 meter (\~ 30 cm / pixel scale) and \>100:1 SNR as a
minimum criterion, with strong scientific interest in higher resolution
should a combination of increased payload mass or improved instrument
technology permit. Current estimates of the mass and cost of a 5-10 cm
resolution camera system led to a majority opinion that this option is
not feasible for an MRO-class payload with several major elements
intended to address multiple scientific themes. A wide-field camera, of
low mass and cost, was also identified as being of high interest.

*Shallow Subsurface Imaging*. The sub-group advocates that MSO
investigate the shallow subsurface of Mars to:

> \(a\) Reveal geologic features associated with habitable settings and
> past environments.
>
> \(b\) Identify and characterize recent impact features over large
> areas.
>
> \(c\) Provide a detailed mapping of ground ice at high latitude as a
> feed-forward to subsurface drilling/sampling.
>
> \(d\) Characterize volcanic and impact features to refine the global
> geologic history.
>
> \(e\) Characterize near-surface rock abundance as a feed-forward to
> eventual drilling in high-priority targets.

\(f\) Search for evidence of ground movement due to volcanic or tectonic
processes as a feed-forward to eventual surface network missions.

\(g\) Search for small-scale topographic changes associated with
sublimation of subsurface ice.

This investigation can be accomplished by a synthetic aperture radar
(SAR) imaging system with wavelength in the 20-30 cm range using the
spacecraft high-gain antenna. Ground penetration of 3 m or more in Mars
surface materials is required. Image spatial resolution of 25 m for at
least targeted areas is required, with lower resolution of 75-100 m
acceptable for synoptic observations. Surface change detection at the
few-cm vertical scale is required.

*Compositional Measurements.* A few investigations developed by the
sub-group point toward composition-related measurements in near-infrared
and/or thermal IR wavelengths. There are two areas where advances in
composition can be made from orbit: 1) Higher spatial resolution thermal
infrared spectroscopy \~ 10-20m/pixel, to fully identify compositional
diversity seen in THEMIS, but not resolvable by TES. In particular,
recent discoveries of quartz and high-silica phases will not be
addressable with CRISM. 2) Very high spatial resolution SWIR
spectroscopy, roughly a few m/pixel, to do precise observations of
locations identified with CRISM/OMEGA.   This may direct precision
landed operations to high priority aqueous mineralogy. There is also a
strong desire on the part of the community to have landed SWIR
spectroscopy to ground truth OMEGA and CRISM, though this was not
considered by the SAG-2.

**Table 6.3 Major Geology Themes and Goals:**

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height="4.634722222222222in"}

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height="5.2243055555555555in"}

##  Geophysics: Landed and Interior Science 

### Background

#### Importance of Interior Investigations for Mars Science

It is no accident that the investigation of the interior of Mars has
been high on the priority list of every NRC planetary science strategy
document since the first COMPLEX report in 1977. Knowledge of the
composition, structure, and history of Mars is fundamental to
understanding the formation and evolution of terrestrial planets in
general, and provides insight into the history and processes of our own
planet. Thus there are compelling scientific motivations for the study
of the interior of the planet in its own right. In addition, the study
of the interior provides important clues about a wide range of topics,
including the early history and geologic evolution, formation and loss
of the atmosphere, geothermal energy and habitability.

Understanding of the interior of Mars is fundamental to the
interpretation of the surface record. Interior processes are the
ultimate driver for both volcanic and tectonic activity. The delineation
of the elementary interior structure (core, mantle, crust) and the
establishment of basic thermal boundary conditions for the planet's
thermal history are essential components to understanding Mars and its
history.

The last 20 years has seen great progress in the modeling of heat
transfer through planetary mantles. The growing capabilities of
computers have allowed numerical studies to take into account more and
more of the complexities of the rocks. The main discovery has been the
characterization of the so-called 'conductive lid' regime: the
convective domain is located beneath a thick lithosphere through which
heat is transferred by conduction. Applied to Mars, this model provides
three main results: 1) The conductive lid is about 200 km thick; 2) The
mantle temperature just beneath the lid is close to melting point; and
3) The core is still liquid.

The velocity of seismic waves traveling through the mantle would provide
information on the thickness of the conductive lid, on the presence of a
partially melted mantle, on the temperature of the mantle and on the
state of the core. Such measurements would provide constraints on the
thermal evolution of planet Mars. But they would also bring new
constraints on the modeling of the thermal evolution of terrestrial
planets. By comparing Mars and the Earth, new ideas will emerge on the
relationship between convection and plate tectonics.

Delineating the structure and dynamical processes of the deep interior
is fundamental for understanding the origin and evolution of Mars in
general, and its surface evolution and the release of water and
atmospheric gases in particular. For example, the thickness of the crust
and the size and composition of the core provide strong constraints on
the bulk composition of the planet and the manner in which it
differentiated. Knowledge of the physical and thermal evolution places
constraints on the composition, quantity, and rate of release of
volatiles (water and atmospheric gases) to the surface. Evidence that
Mars had a magnetic field early in its history has important
implications for its formation and early evolution, as well as for the
retention of its early atmosphere.

The intense interest in the possibility of life on Mars provides
additional emphasis for these investigations. The possible formation of
habitable zones at or near the surface of Mars is tied inextricably to
the origin and evolution of the planet as a whole. In particular, the
bulk composition, differentiation, and thermal/chemical evolution of the
interior governed the magnetic dynamo, provided the crustal foundation
and basic chemical building blocks, and drove the volcanic and tectonic
processes that have shaped the surface and the
atmosphere-hydrosphere-cryosphere system through time. For example, the
delivery of mantle-derived volatiles to the surface via volcanism is a
key factor in the evolution of the atmosphere and water budget. The
timing and character of the early dynamo may have played a crucial role
in shielding the early atmosphere and surface, providing a conducive
environment for pre-biotic chemistry. Regional variations in the
subsurface thermal environment may modulate the locations and timing of
habitable zone development and evolution.

Thus understanding the interior and atmosphere contributes directly to
understanding the habitability of Mars, primarily in the past, but also
in the present in terms of such things as the oxidation state of the
mantle (relating directly to possible non-biogenic origins of
atmospheric methane) and the availability of geothermal energy for
sustaining biotic processes at depth. And in a fundamental sense, the
interior processes that resulted in the present planet must be
understood in order to be able to separate their geochemical patterns
from possible subtle chemical biosignatures. Any putative direct
detection of life (e.g., ALH84001) or lack thereof (e.g., Viking)
without a broader understanding of the system in which that life must
exist and with which it must intimately interact will be fraught with
uncertainty.

However, despite these arguments, the interior of Mars remains largely
unexplored with critical gaps in our understanding of how Mars evolved
as a planet.

#### Single Station vs. Network Measurements

The most effective method for probing the deep interior of Mars is with
a widely distributed network of at least four landers carrying
seismometers, heat flow probes, magnetometers and precision tracking
systems. Such an ambitious mission has been repeatedly recommended by
the NRC, and is being considered for a future launch opportunity by the
Mars Exploration Program. But given that measurements constraining the
structure and processes of the deep interior are virtually nonexistent,
any information that a single station could obtain would result in a
significant leap in our understanding of the interior structure. It
would also provide a strong foundation for more effectively planning for
a future network.

*Seismology.* A network configuration is particularly valuable for
seismic investigations. It provides wide geographic coverage allows for
the straightforward use of body wave arrival times at multiple locations
to identify and locate seismic events in space and time, and to derive
seismic velocity structure. Arrival times are the most straightforward
measurements that can be made on seismic records, and this is the method
by which most of the information on the interior structure of the Earth
and Moon has been acquired. In addition, the redundancy and spatial
coverage (allowing proximity to more potentially seismogenic regions)
provides significant robustness to a seismic experiment that will not be
available to a single station. However a seismic signal is extremely
rich in information content, and there are numerous methods by which the
characteristics of its source and path can be derived. Many of these can
be effectively applied to the measurements from a single seismic
station, and will be described in the following section.

*Heat Flow.* There are several reasons for which a distributed
collection of heat flow measurements are desired. First, heat flow from
the interior is not expected to be spatially uniform across the surface
of Mars. Variations in regional volcanic activity or the distribution of
radiogenic elements in the crust can cause significant differences in
heat flow. Also, deriving the heat flux from the interior requires that
its temperature gradient be separated from other signals due to diurnal,
seasonal and climatic variations in the surface temperature. The first
two of these can be overcome by measuring temperature to a few meters
depth. But the climatic variation expected from changes in the obliquity
extends beyond the depths, which are likely to be achieved in the
foreseeable future. Fortunately, this signal has a latitudinal variation
that, if sampled, can be used to identify and correct for it.

Thus multiple measurements will eventually be required to accurately
characterize the mean heat flow of Mars. But these measurements do not
have to be taken simultaneously; such a collection can be accumulated
over many years. A single measurement will constitute a valuable first
step toward this objective, and will provide our initial insight into
the thermal state of the interior.

*Precision Tracking.* A network would enormously increase the value of
surface tracking measurements over that of a single lander. Previous
tracking of Viking and Pathfinder spacecraft on the surface of Mars has
resulted in a significant improvement in our knowledge of the moment of
inertia (and thus the size and composition of the core) by measuring the
precession. Another station with a dedicated radio science experiment
would result in an order of magnitude improvement in this parameter due
to advances in radiometric measurement capability and an extension of
the time series initiated during the Viking mission. Simultaneously
tracking multiple locations on the surface would further improve the
accuracy of this measurement. If multiple latitudes were accessible, it
would allow for a direct measurement of the polar motion, adding
nutation and polar motion (e.g., Chandler Wobble) to our arsenal of
interior constraints, further refining estimates of core parameters
(liquid vs. solid, presence or absence of an inner core) and mantle
inelasticity (related to thermal state). It should be emphasized,
however, that valuable measurements can be made from a single lander
that will greatly increase our knowledge of interior structure.

*Preparing for Future Missions.*

With the failure of the Viking seismic experiment to return data on the
seismic characteristics of Mars, future seismic networks missions are
faced with the difficult task of preparing for the widest range of
possible situations. Not only is the rate and spatial distribution of
seismicity only estimated from first principles, but the level, spectral
character, and temporal variability of seismic background noise is
completely unknown. Similarly, the character of Martian seismic events
as manifested in seismograms can only be guessed at by analogy to the
Earth and Moon. The lunar experience provides a cautionary tale, in that
the many seismic events recorded by the Apollo 11 seismometer were not
recognized as such until a known event (the crash of Apollo flight
hardware) revealed that much of what had been interpreted as noise were
actually moonquakes with unanticipated and dramatically un-Earthlike
characteristics. With no a priori knowledge, it is necessary to maximize
all the measurement parameters (e.g., sensitivity, bandpass, number of
stations, etc.) in order to assure the success of the mission.
Measurements from a single "pathfinder" seismometer, with sufficient
sensitivity and observation time, could prove valuable in relaxing
requirements and simplifying the design for a future full network
mission.

### Priority Goals and Measurements

The first-order objectives of a geophysical lander are to determine the
seismicity (seismic activity and distribution; impact frequency), and
provide information on crustal thickness and structure; core size,
density and state (liquid or solid); seismic structure of the mantle;
and thermal state of the interior.

#### Seismic Activity and Impact Frequency

One of the greatest uncertainties in using a single station to provide
bounds on interior structure is whether a sufficient number of quakes
will be detected of sufficient magnitude to provide useful results. The
lack of detection by the Viking seismic experiment (which was woefully
insensitive) is consistent with an upper estimate of the Martian
activity comparable to the Earth's intraplate activity. Theoretical
estimates from thermoelastic cooling and surface faults predict a level
of activity within this bound but still \~100× greater than the shallow
moonquake activity detected on the Moon. This level would provide
\~10-50 quakes of seismic moment ≥10^15^ Nm (roughly equivalent to
terrestrial magnitude m~b~=4) per year (throughout Section 6.3 we will
use the term "year" to refer to an Earth year, roughly one-half Mars
year). Quakes of this size should be globally detectable by a
seismometer with a sensitivity of 10^-9^m/s^2^ or better. Many more
smaller quakes (from terrestrial and lunar experience there should be
\~25× more quakes for each unit decrease in moment magnitude) will be
detectable if the station is located relatively nearby (within few
thousand km).

Distribution of seismicity can be determined by monitoring the body wave
frequency band (\~0.1-2.5 Hz) for seismic events. The approximate
epicentral distance can be derived from the differential P-S travel time
on the vertical record. The error in epicentral distance will be \~10%
(roughly the differences among a-priori of Mars seismic models), which
will improve as interior models are refined. The azimuth can be measured
using the horizontal components, yielding an error of \~15% in azimuth.

Thus given enough measurement time (at least an Earth year, to account
for the large uncertainties in current estimates), a single sensitive
seismometer should be able to determine the seismic activity of Mars*.*
The level of seismicity gives a measure of the current level of tectonic
(and perhaps volcanic) activity, both in terms of intensity and
geographic distribution. Current estimates of seismicity depend on
theoretical thermal cooling calculations or extrapolation of historical
faulting. Thus the measurement of seismicity, regardless of the actual
number of events detected, will provide fundamental information about
the dynamics of Mars, providing insight into current levels of tectonic
deformation.

The unique characteristics of impact seismograms allow them to be
differentiated from endogenic events. These seismograms can thus provide
a direct measure of the current rate of impacts, along with an estimate
of their sizes. Hundreds of impacts per year were seen on the Moon, but
the environment of Mars is very different. Asteroids strike Mars at an
average velocity of 10 km/s rather than 20 km/s at the Moon, so impact
energy is reduced by about a factor of four. The thin Mars atmosphere is
able to disrupt weak bolides and decelerate small objects. Regolith is
generally thinner or indurated on Mars compared with the Moon, but
aeolian mantles are common. There are far fewer craters smaller than 10
m diameter on Mars compared with the Moon, except in secondary fields.
Most of the small objects (mostly asteroids rather than comets) that do
impact the surface make shallow craters and clusters of craters,
indicating that these impacts are due to clusters of objects rather than
intact rocks. Malin et al. (2006 Science) reported 20 "new" or darkened
spots that correspond to fresh impact craters over 1/6 of the Martian
surface in the MGS era (\~5 years average time span for observation of
changes). HiRISE images indicate that about half of the impacts have
experienced aeolian modifications and may be older than the MGS era.
Based on these results we should expect \~10 to 20 impacts per year of
sufficient magnitude to create 10 m or larger craters, likely detectable
as seismic events. Several of these MGS-era impacts are associated with
concentrations of dust avalanches, perhaps triggered by seismic shaking.
Note that the approximate locations of such events can be used to target
orbital imaging to look for the resulting new craters on the surface.
The combination of an impact seismogram with an image-based impact
location provides a powerful tool (comparable to the Saturn IVB lunar
impact) for probing the crust.

#### Crustal Structure

Several independent methods can be used to determine crustal structure.
The receiver method (using body wave mode conversions at the base of the
crust) has been successfully applied to the Moon. This method has the
advantage of not requiring larger quakes that are necessary to produce
surface waves and normal modes. A second approach would be to use
natural impacts as described in the previous section. This method would
be analogous to the Saturn IVB impact experiment on the Moon, which
produced the best Apollo-era estimates for lunar crustal thickness.

Another method uses the group velocity dispersion of surface waves at
lower frequencies (10-100 mHz) from the records of relatively large
events. Such dispersion curves are very sensitive to the crustal
thickness, and well-developed surface wave trains can be used to model
the large-scale vertical structure of the crust (and the uppermost
mantle). The drawback of this method is that surface waves are not
generated on Earth for quakes smaller than magnitude \~5. Thus this
method would require the detection of relatively rare events, although
several would be expect within a year of observation if current activity
estimates hold.

#### Mantle Structure

For a single seismometer, the most effective techniques for studying
deep structure utilize normal mode frequencies, which do not require
knowledge of the source location. Normal mode peaks from 5-20 mHz (the
frequency range sensitive to mantle structure) can be identified for a
detection noise level of 10^‑9^m/s^2^/Hz^1/2^, and these spectral peaks
can be inverted to derive the radial structure of the mantle. This
structure is particulars sensitive to compositional stratification or
polymorphic phase transitions. A useful analysis can be accomplished by
using single record of a large quake of moment ≥10^18^Nm (equivalent
m~b~\~6) or by stacking quakes with an equivalent cumulative moment.
Again, this requires relatively rare, but reasonably expectable events.

#### Core Structure

Precision tracking of a single station, using an X-band direct-to-Earth
carrier (or dual frequency tracking, X-band and UHF, through an orbital
relay asset) can be used to infer interior structure from its effect on
variations in the orientation of Mars with respect to inertial space.
The precession, nutation, and polar motion of Mars result from the
interaction of the interior mass distribution with the gravity of the
Sun. Analyses indicate projected improvements over Viking and Pathfinder
of a factor of 10 in precession, resulting from the increased total time
span since Viking and a longer contiguous time span (1 Mars year vs. 90
sols for MPF) and better data accuracy (particularly with respect to
Viking). This would provide a considerable (better than a factor of 5)
improvement in the estimate of the size of the core and its density.

A capable very-long-period seismometer may also be able to contribute to
the determination of core size through the measurement of the Phobos
solid tide amplitude. Detailed modeling has shown that for a seismometer
of the sensitivity discussed above (at the Phobos orbital period, 7.65
hours) this measurement is limited by the temperature noise. But because
of the periodic and continuous nature of the signal, long-term stacking
can be employed and a year-long time series should yield a
scientifically useful core signature.

#### Thermal State

Surface heat flux (heat flow) can be measured by determining the
subsurface temperature gradient with a string of thermistors distributed
at depth, along with a corresponding thermal conductivity determination
(typically derived from heat pulse decay observations). These
measurements must extend down at least three meters in order to sample
below the annual thermal wave. The main difficulty is penetrating to
depths ≥3 m using a relatively modest resources of a lander. Whereas
drilling to these depths is still complex and expensive, recent
developments of self-hammering penetrators (such as that flown on
Beagle-2) show promise for being able to relatively inexpensively deploy
thermal strings at depths up to 5 meters.

In addition to observing the thermal boundary, it is possible to obtain
information on the temperature profile of the deep interior using
electromagnetic sounding methods. The most mature of these methods
(applied to the Moon during the Apollo missions) uses a magnetometer on
a surface station to measure the magnetic response of the planet to an
external time-varying field (in this case supplied by Mars' ionosphere)
as a function of frequency. From this information, one can obtain the
resistivity profile, which can be interpreted in terms of rock
temperature, to depths of thousands of kilometers. However this method
requires independent knowledge of the inducing field, either from
simultaneous orbital magnetic measurements or by measuring the
low-frequency electric field vector at the surface station itself.

**Table 6.4 Geophysics: Landed and Interiors Goals Matrix - Single
Station Assumed**

![](media/image1.pct)

7.  []{#__RefHeading___Toc42082102 .anchor}Strawman Instruments

Overall, the SAG-2 members were opposed to being overly specific with
regard to instruments that would make the observation and measurement
goals described in the previous section. In an effort to constrain
mission implementation and resource liens, strawman instruments were put
forth by each group. These instruments are proposed as an "existence
proof" to achieve science objectives described in section 6. It is
recognized that other instruments may be able to achieve the measurement
and science goals previously identified and the higher-level goals
should be referred to in order to achieve the broadest possible creative
contribution from the science community at large.

The instruments are briefly summarized below, more or less in order of
atmospheric, polar, geology and geophysics, though several instruments
support goals and objectives in multiple groups. If there were higher
priorities among the submitted instruments these are noted.

Cost and mass estimates were made by the SAG-2 members with familiarity
with such instrumentation and were checked against values for similar
instrumentation carried by the MSO project office. As an additional
reality check, the MRO payload was made from our equivalent strawman
instruments and was found to be consistent. Specific heritage is noted
below and cost and mass estimates are provided in the mission scenario
table in Section 8. Cost estimates do not include Phase E costs or
reserves as these are carried separately. We did not consider the cost
of either the lander delivery system or the orbiter accommodation for a
lander in our scenarios. Specific mission liens such as orbital altitude
and inclination, spacecraft roll and stability are addressed for each
instrument. Data rate was suggested to be equivalent to MRO, or \~
50Gb/day, particularly if multiple imaging instruments are involved.

## Solar occultation FTIR

A solar occultation Fourier-transform infrared spectrometer with
spectral resolution \~0.02 cm^-1^ over 850-4300 cm^-1^ has sufficient
signal-to-noise and spectral discrimination to achieve the parts per
trillion detection sensitivity for the suite of target signature gases.
Solar occultation, with its intense source, provides the ability to
achieve simultaneous measurements of the vertical distribution of
multiple chemical species from the surface to 100 km, including in
moderately dusty conditions. Such devices have been used to characterize
important trace constituents in the Earth's upper atmosphere (e.g.,
MATMOS, ACE). For solar occultations, the global coverage is controlled
by the inclination of the spacecraft orbit. As the inclination increases
more poleward of 74°, frequency of sampling, particularly at low and
mid-latitudes, is compromised. The minimum mission requirement is to
observe most latitudes at least once per Mars season and orbit trades
were studied by the project and are discussed in more detail in Section
9.This instrument would need a large passive radiator or active cooling.
Active cooling may add substantially to the cost and mass estimated in
Table 8.

## Sub-millimeter spectrometer

A submillimeter spectrometer observing in a wavelength range near 600
GHz, with a viewing geometry varying between nadir and limb views, can
profile specific atmospheric trace signature species (including water)
and temperature on a global scale with high horizontal resolution. (Not
all trace molecules could be observed in this mode.). In this operating
wavelength range, observations are unaffected by the presence of dust;
species and temperature measurements can be acquired within the depths
of the densest dust storms, allowing specifically the investigation of
the potential influence of heterogeneous chemistry, including processes
related to dust electrification. The submillimeter spectrometer in its
limb-observing mode, through measurement of the Doppler shift of
spectral features, can measure the wind velocity along the line of
sight. This new element is important both for understanding the
atmospheric circulation in general and in using inverse modeling to
identify source regions for the signature gases as put forward by both
atmospheric science and polar groups. No specific mission liens were
identified.

##  "MARCI-like" Camera

A wide-field visible imaging system provides additional information on
the global distribution of atmospheric dust and ices and global surveys
of surface albedo changes. This instrument continues MGS/MRO
atmosphere/surface monitoring and provides global dust distribution. It
supports multiple objectives in atmospheric, geologic and polar
processes. The MOC wide-angle mode and MARCI cameras are similar to what
is envisioned for this instrument.

## Thermal IR or "Lite" spectrometer system

This instrument can address multiple objectives or goals, depending on
final design and configuration. An instrument of this class, similar to
MGS-TES or MRO-MCS was envisioned to provide the daily global
measurements of atmospheric dust and ices for correlation with species
and temperature measurements from the submillimeter spectrometer under
atmospheric state goals. It would provide input for model simulations by
constraining the solar heating driving the circulation related to energy
balance or dust/volatile exchange in measurements of climate and polar
processes. A system with improved spatial and spectral resolution above
that of TES can provide detailed mineral mapping of diversity seen in
THEMIS data, in support of geology goals. Spatial resolution of 10 to 20
m at spectral resolution better than TES is achievable with modern
technology and cooled systems.

## "HiRISE" Class Imager (HCI)

A high resolution (sub-m/pixel), high signal-to-noise camera system of
capability and mass similar to the MRO HiRISE instrument was considered
a high priority by all three, but especially the polar and geology,
groups. HiRISE provides images at 30 cm/pixel scale over a 6-km wide
swath from 300 km altitude, and with at least 100:1 SNR. HiRISE on MRO
can cover \~0.2% of the Martian surface at full resolution per Earth
year in the mapping orbit. The utility of a comparable instrument on MSO
is in additional coverage beyond that attainable with MRO, continued and
longer-term monitoring of active processes, and the opportunity to image
at different illumination angles. HiRISE-class imaging is widely
considered by the engineering and landing site community to be the
minimum capability required to support future landing site surveys. This
camera system must permit viewing geometries commensurate with stereo
mapping at high vertical and horizontal resolution over targeted areas.
For polar processes a minimum orbital inclination was found to be 85
degrees in order to clearly observe most of the residual ice caps of
both poles as well as observe detailed changes in the south residual
CO~2~ ice cap. Arguments were made to support a drifting local time of
day, in particular the ability to re-image sites over a wide variety of
illumination angles, which enables significantly greater information and
understanding of small-scale features. Based on the HiRISE experience
off-nadir pointing of the spacecraft needs to be allowed up to 30
degrees cross-track and spacecraft pointing stability of \~2
microradians (3 sigma) over 10 ms is required. Cost and mass was
estimated based on HiRISE. Significant improvements to the focal-plane
system may be possible if a few extra kg are available. It would also be
possible to design a focal-plane system that tolerates poorer pointing
stability while maintaining image quality.

## Multibeam Lidar Altimeter + Ultra Stable Oscillator

In order to address multiple objectives related to polar mass and
density of the seasonal cap, polar night energy budgets, cloud motions
and atmospheric dynamics, the polar splinter group proposed a high
vertical precision multi-beam lidar altimeter. The proposed Multibeam
Lidar Altimeter is assumed to be similar to LOLA, scheduled for flight
on the 2008 Lunar Reconnaissance Orbiter and aspects of the system are
inherited from the successful CALIPSO lidar, which is presently
operating effectively in low Earth orbit. Its vertical ranging precision
is on the order of centimeters, an order of magnitude better than
MGS/MOLA. New laser transmitter technology has longer lifetime and
greater number of pulses, so that contiguous-footprint samples
approximately 15-20m along-track can be produced, as part of an array of
parallel beams as widely separated as kilometers to facilitate rapid
sampling and densification of surface altimeter cross-overs. A three to
five beam lidar altimeter that employs waveform-based echo recovery to
further refine its ability to resolve cm-scale ranges and to quantify
the within-footprint vertical structure (as roughness) and reflectivity
(at the laser wavelength of 1064nm) is now achievable, with the
additional capability of being able to resolve optically-dense
atmospheric phenomena (i.e., clouds, hazes, hoods) at vertical scales as
fine as 150m and along track at kilometer scales, from the top of the
atmosphere to the surface. Such an instrument would significantly
constrain the seasonal mass budgets, and it would do so with spatially
resolved measurements with a factor of 20 increase in sampling density
and 10 times higher vertical precision. This instrument could also
produce a global, seamless digital elevation model (DEM) for Mars at
better than 100m horizontal grid scale, with 3-10cm (RMS) vertical
accuracy, and a related map of 100m scale vertical roughness with
sensitivity to vertical structure at the 10cm level. Such products would
support investigations in the Geology and Atmospheric Signatures and
State theme areas, and also support autonomous precision landing
solutions for eventual human exploration. In order to determine
atmospheric mass in exchange with the surface an Ultra Stable Oscillator
(USO) and radio science experiment to concurrently constrain atmospheric
pressure must also be included (ideally employing the X-band mode of the
MSO telecom system). Orbital inclination for optimized polar cap
sampling should be between 85 degrees and 92.8 degrees. Inclinations
below 82 degrees will degrade the ranging precision for the polar
regions, but would still allow for sampling.

## Multi-spectral SWIR/TIR or "Capable" Spectrometer

This instrument can fulfill varying objectives depending on how the
instrument is configured. As envisioned by the polar group this
instrument would combine both reflected solar and emitted thermal
wavelengths, similar to the terrestrial ASTER instrument. The instrument
would have approximately 30 SWIR channels at critical wavelengths for
diagnostic ice and mineral spectral features and spatial resolution of
roughly 100m. The TIR would have roughly 10 channels, plus optical and
thermal bolometers at spatial resolutions equivalent to TES. Spatial
coverage should be broad enough to allow frequent observation of
seasonal and annual surface processes that are highly variable in space
and time. This would allow high time resolution of seasonal processes
and selected channels can clearly separate water, carbon dioxide, and
dust while concurrently monitoring optical and thermal energy balance
(via bolometers) for atmospheric transport and exchange. The goal is to
quantify composition, dust content and variability, in addition to mass
fluxes, supporting the altimetry measurement. An alternate view of this
component is that is can represent a more capable high spectral
resolution spectrometer system with higher spatial resolution to follow
up on either CRISM or THEMIS discoveries. Heritage from the terrestrial
community include Artemis, designed for military target identification
from Earth orbit. These systems will probably require both passive and
active cooling.

## 1-m resolution camera

The SAG-2 considers the equivalent of HiRISE spatial resolution as the
minimum required for multiple science goals for imaging systems. In
order to create mission scenarios that fit in the lowest POP cost
guidelines a less capable imaging system needed to be included. This was
proposed to be a MOC equivalent, or better than CTX, at roughly 1m/pixel
and color capability is desired. Such an imager would have few
advantages over a HiRISE class imager but it would be able to cover a
greater area of Mars and provide better detection of changes if they are
both resolved and understood at 1 m/pixel.

## Synthetic Aperture Radar

A synthetic aperture radar (SAR) imaging system capable of penetrating 3
m or more of typical Mars surface material was suggested to reveal
buried geologic features. This system must also be capable of measuring
surface deformation at the few-cm scale through repeat-pass
interferometry (InSAR). Published studies of Mars SAR applications show
that a radar wavelength of 20-30 cm is appropriate for these
investigations, based on conservative estimates of the near-surface loss
tangent and expectations of achievable instrument signal-to-noise
performance. One major accommodation issue for a SAR relates to the
antenna, which must be carried as a separate 35-40 kg item unless the
spacecraft high-gain antenna can be shared between telecom and radar
imaging. The SAG-2 recommends that the dual-use option be facilitated in
order to make a SAR feasible within the broad goals of MSO. An
additional requirement is that the antenna must be at least 3m for
optimal imaging resolution. A high-bandwidth SAR operated at nadir could
provide additional information about the shallow, layered structure of
the polar regions, with horizontal and vertical resolutions an order of
magnitude improved over MRO's SHARAD. This SAR "mode" is of interest to
the climate and polar processes theme-based goals of MSO. The
technologies required for this type of instrument have been long
demonstrated in both airborne (e.g., the NASA/JPL AIRSAR) and spaceborne
systems (Magellan, Cassini SAR).

## Landed Geophysics

A complement of three elements were envisioned to be the science
baseline to justify a single drop off package (DOP). In priority order
these are: landed seismology; precision tracking for geodetics; and heat
flow/magnetics. This complement can meaningfully address the science
goals outlined previously. We note that examples of all the instruments
described in this section exist with TRL ≥ 6.

It is important to realize that a highly capable seismometer is
necessary in order to justify the single-station experiment. As
described in Table 6.4, there are specific requirements on sensitivity
and frequency needed to obtain scientifically useful information
relative to the science objectives. For example, a short-period
seismometer (sensitive to frequencies \> 0.1 Hz) can measure seismicity,
impact flux, and may provide some constraints on crustal thickness, but
will not contribute meaningful data on the deep structure of the planet.
And given the uncertainty in the level of seismic activity, observing
the seismic environment for significantly less than an Earth year may
put even the basic determination of seismicity at risk.

A high level of precision tracking can be obtained by using a dual
frequency system (e.g., UHF plus X-band) in order to cancel the path
noise from variations in the ionosphere electron density. Thus the
precision tracking experiment requires an additional X-Band transponder
in addition to the basic UHF telecom system.

While the heat flow/magnetometer element was judged the lowest priority
element of the lander payload, the SAG-2 included these instruments in
the full desired science complement. The heat flow measurement is a
difficult one, although ongoing development of self-penetrating "moles"
show promise for making this measurement practical. A magnetometer is
also at a lower science priority, although its low mass, power
requirement and cost combine to make it an attractive addition.

It should be emphasized that the capabilities of the lander itself play
an integral role in enabling these geophysical measurements. As a basic
requirement, the lander must be able to deliver sufficient payload mass
to the surface to allow instruments with the necessary capabilities. It
must be able to support their minimum power and telemetry requirements.
The seismometer and heat flow probe require direct access to the ground
in order to properly make their measurements. For minimum science, the
landed instruments need to operate for at least 0.5 of a Mars year and a
full Mars year is highly desirable. Although there is room for
compromise in all these areas, there are minimum levels beneath which
the experiments will not be scientifically worthwhile.

## Landed Meteorology

47The scientific objectives of the Atmospheric State landed science are
achievable only with a highly integrated set of instruments. The
integrated nature of the package is required because many of the
observations only have full value when combined with each other. In
addition to the instruments themselves, a boom is required to remove
many of the observations from the disturbed conditions near the lander.

Pressure and temperature measurements can be obtained with instruments
only slightly improved from those used on Pathfinder and Mars Polar
Lander. Surface temperature and boundary layer atmospheric temperature
profiles (and thus atmospheric back-radiation) can most simply be
measured with a system similar to that being used on MSL REMS. This
system is a set of thermopile detectors, each behind its own
interference filter window, tuned to select either continuum thermal
emission, dust, water or ice absorption features, or specific bandpasses
in 15µm CO~2~ band. The 3-D winds can be measured to the required
precision and sampling frequency with a sonic anemometer. This
instrument is also a fast-response thermometer, directly allowing the
sonic anemometer to measure the eddy fluxes of both momentum and heat
through the Martian boundary layer. A Tunable Diode Laser hygrometer
(descended from those flown on Mars Polar Lander) can measure the water
vapor present with sufficient accuracy and sampling frequency to meet
the measurement requirements. When this is properly integrated with the
sonic anemometer, these two observations can be combined to directly
yield the water vapor flux. Finally, a vertical electric field sensor,
sensitive across a broad range of field strengths can achieve the
science goals outlined above concerning dust electrification. Such an
instrument was developed for Mars03 MATADOR/ECHOS, and was tested
terrestrially under similar conditions in the MATADOR field campaign.

8.  []{#__RefHeading___Toc42082114 .anchor}Mission Scenarios

With strawman elements as defined in Section 7, the SAG-2 next
considered how to combine various elements into mission scenarios that
fit the core mission attributes (Section 3) with science synergies among
the elements and potential for either follow up on existing program
elements or feed-forward to future proposed missions such as AFL, Twin
Mid-Rovers, a Long-Lived Network or MSR. In an open "brainstorming"
phase, members of the SAG-2 suggested reasonable combinations and
upwards of a dozen individual scenarios can be envisioned that combine
elements to address broad goals of habitability, dynamics, or planetary
evolution.

It became rapidly clear that because of the cost and mass limitations
suggested for MSO not all high priority science objectives can be
accommodated and significant orbital science will remain unaccomplished
even after MSO. Given that no one mission scenario could be created with
"something for everyone", the group sought to combine and refine
scenarios that had the most desirable science elements addressing goals
from two or more of the discipline (theme-based) splinter groups.

These possible combinations were grouped into three main categories: A
Core Mission Concept (CMC), a "Reduced" example, and an "Augmented"
version. "Reduced" and "Augmented" are with respect to the CMC. While
these combinations are not the only ones that can be envisioned, the
SAG-2 felt they represented the most reasonable trade space by retaining
complementary science goals and exploring the range of cost guidelines
as provided by the MSO Project and the NASA HQ Charter.

The Core Mission Concept was constructed to provide the best combination
of instruments addressing the high-priority science goals within each
science scenario while keeping key cross-disciplinary elements within
reasonably constrained resources of mass and cost. The gain in science
for the modest augmentation needed for the CMC was very high and it
preserved the innovative, cross-disciplinary elements that are the
hallmark of a core mission, as discussed in Section 3. In all three
scenarios the Reduced case makes serious compromises with regard to
measurement goals, to future mission support, or by supporting fewer
cross-disciplinary elements.

These mission scenario plans (A, P, G) and the strawman instrument
complements associated with each are shown in the following table. Here
color and \* or \*\* are used to denote instrument substitutions and
descopes between the Core Mission Concept and the Reduced level, while
color (orange, red) denotes alternate Augmented plans.

While augmented scenarios are outside the provided cost guidelines,
these were in line with MRO flight system capabilities and allow the
opportunity to pursue contributed elements for specific science
objectives. In particular the SAG-2 is aware of Canadian, French, German
and Italian instrumentation similar to many of our proposed strawman
instruments and these contributions should be encouraged to achieve the
most capable and interdisciplinary payload.

![](media/image2.pct){width="6.25in" height="4.968055555555556in"}*Table
8: Mission Scenarios*

[]{#__RefHeading___Toc42082115 .anchor}

## Plan A: Atmospheric Signatures and Near-Surface Change

This plan follows up on recent discoveries of methane and active gullies
(with implications for possible shallow subsurface liquid water) and
fulfills the charter task to examine atmospheric trace gasses. The
science return of the Core Mission Concept payload will fulfill all the
key objectives of the Atmospheric Signatures and Atmospheric State
(orbital science) investigations (6.1), many objectives of the Geology
goals (6.3), and a few objectives identified under Polar Processes and
Modern Climate (6.2).

Plan A payload elements will provide a comprehensive characterization of
the chemical composition of the Martian atmosphere, its global
distribution and variation with Martian season, with particular
sensitivity for ultra-low abundance species that might be signatures of
subsurface processes related to existing habitable zones and possible
life. The payload elements will continue the record of global climate
measurements of atmospheric temperature, dust, water vapor, and surface
albedo and, in addition, provide new measurements that uniquely
constrain and validate models of atmospheric dynamics and state,
including direct measurements of winds. The submillimeter spectrometer,
one element of the Plan A existence proof, will provide atmospheric
state measurements under all atmospheric conditions. The simultaneous
measurement of atmospheric state and composition enhances the capability
to follow a detected atmospheric signature back to its surface source.

Provision of a HiRISE-class imager continues global observations capable
of finding recent changes in surface features indicative of extant
active processes and provides landing site imaging support for later
missions, including exploration of zones of interest as defined by trace
gas distributions.

Two augmentation options in particular have been identified. One
augmentation option is the inclusion of a SAR to provide a new
measurement approach for identifying topographic surface change and a
new perspective for characterizing near-subsurface geological structure.
This complements the atmospheric interest in active subsurface
processes. The second augmentation option includes both a landed
geophysics package and a landed meteorological station. The latter
payload element is directly synergistic with orbital atmospheric science
as described in §6.1.3.4 earlier in this report. Both the landed
geophysics experiments and the Atmospheric Signatures payload elements
potentially provide complementary evidence for extant volcanic
processes.

In a "reduced" option, the Plan A payload has a 1-meter resolution
camera instead of the HiRISE-like resolution imaging. This can continue
global monitoring of surface change with reduced sensitivity and has
reduced value for landing site imaging.

All versions of Plan A provide frequent, extensive measurements of
atmospheric composition and state in polar regions that support an
understanding of the seasonal exchange of volatiles between the polar
caps and the effect that the seasonally-varying polar caps have on
atmospheric conditions. In addition, detection of time-varying release
of atmospheric signatures from polar regions is provided in all Plan A
configurations.

The combination of trace gas measurements and surface imaging may
provide uniquely useful guidance impacting on landing site selection
particularly for AFL and MSR. The atmospheric state measurements alone
will support future entry/descent/landing for any mission equator ward
of \~74° and similarly for surface imaging feed forward to landing site
selection. The augmentation in which the SAR is added to the payload can
have feed forward for planning subsurface access. The augmentation in
which the landed science element is a part of the payload provides an
important precursor for a future landed network mission.

The primary mission constraint is the lower orbital inclination (74°)
preferred by the solar occultation FTIR instrument to provide frequent
measurements at each latitude to enhance detection of sub-seasonal
variation in atmospheric signature surface sources. At this inclination,
Atmospheric State measurements during two seasons can be acquired at
least twice at different local times throughout the daily cycle, which
will support identification of never previously characterized
atmospheric phenomena that require separation from the seasonal signal
to be understood. In addition, imaging of a common portion of the
surface at different local times can enhance detection of sub-resolution
objects as discussed earlier in this report. On the other hand, at this
inclination, both optical and SAR imaging of the polar surface above
latitudes of approximately 77° will be excluded. However, future landed
missions most likely will target locations at lower latitudes, so this
should not compromise the imaging required for most landing site
surveys.

## Plan P: Polar and Climate Processes 

Plan P approaches the orbital imaging and geophysics elements of the
charter through the lens of current polar processes and climate,
addressing priority goals described in Polar (6.2), Geology (6.3) and
Atmospheric State (6.1.2) sections. This scenario follows up on
discoveries of active erosion of the residual south CO~2~ ice cap and
possible new results from the 2008 Phoenix polar lander which may
increase the priority of landing in more polar regions for biological
potential and climate studies. The residual north cap is the only
surface reservoir of water and may be an important resource for future
human exploration, and serves as the major source of water known on the
planet.

Recent discoveries by MARSIS and SHARAD are showing that the polar
layered deposits, once assumed to be sediments, are in fact largely
dust-free water ice. Understanding how ice and soil-covered ice develop
over time has implications both for short term and longer climate
feedback mechanisms including both albedo and water availability. At the
core of this lies a better understanding of the polar energy balance,
both in annual and seasonal processes. Aside from landed polar science,
the next highest priority observations recommended at the 4^th^
International Mars polar conference were better constraints on the mass
and energy budgets of the polar regions. In the Core Mission Concept,
Plan P approaches the mass/energy balance through detailed monitoring of
both poles in 4 dimensions, x,y,z,t using optical, near-infrared and
thermal infrared imaging spectroscopy for albedo temperature and
composition, multibeam laser altimetry for topography and mass exchange
and high resolution imagery. Atmospheric winds and transport of dust and
volatiles in and out of the polar region is supported by infrared and
sub-mm spectroscopy, as well as via high-resolution atmospheric lidar. A
global synoptic view and continuation of the decadal climate record is
provided by a MARCI like imager. These instruments are also useful
elsewhere on the planet for detailed topography and volume measurements,
monitoring surface and atmospheric change and composition.

The augmented scenario includes near-surface imaging by means of
high-bandwidth SAR to support identification of soil mantles over ice or
layers in the interior of the residual ice sheets and PLD. An alternate
scenario would include higher spatial resolution neutron spectroscopy.
This latter scenario emerged very late in the process and the SAG-2 did
not have sufficient time to consider it in detail as is further
described in section 11.1.5.

The reduce scenario is restricted to the highest priority observations
of the coupled surface/atmosphere exchange. The imaging capability is
reduced and the compositional information is reduced to a simplified
spectrometer for atmospheric temperature profiles, not the detailed
composition and thermal mapping with season.

This scenario is expected to feed forward into the potential for polar
landed missions (i.e., including possibly a polar AFL or one of the twin
Mid-Rovers) or to provide a polar location constraint if a long-lived
network (ML3N as per NRC Decadal Survey) should include at least one
polar station. Imaging and SAR support landing site surveys and drilling
potential at all locations on the planet. The multi-beam lidar would
support development of a global DEM of the planet relevant to other
themes and to future human exploration because of its high vertical
accuracy and geodetic control.

To fully define the atmosphere-surface interactions, scenarios in which
the preferred orbit drifts in local time of day were considered. Both a
drifting local time of day and a fixed local mean solar time can work
effectively in this scenario and should be studied in more detail by the
follow-on SDT.

For climate and polar processes, orbital inclinations must support nadir
polar measurements, so that inclinations from 85 deg to 92.8 deg are
highly preferred. Inclinations below 85 degrees will severely limit the
capacity to meet the Plan P objectives.

## Plan G: Geological and Geophysical Exploration 

Plan G satisfies three of the four specific requests of the MSO-2
Charter: (1) Science from a camera that would also support certification
of future landing sites, (2) Orbital Geophysics, and (3) Landed
geophysical package. It does not address the question of trace gasses,
except in the augmented version. Plan G fully addresses both the Geology
and Geophysics science goals described in Sections 6.3 and 6.4.
Additional science from HiRISE-class imaging (HCI) would follow up on
discoveries such as the present-day (last decade) impact events and
debris flows associated with gullies. Continued long-term monitoring and
detailed characterization of such events provides key constraints on
understanding "Mars Today." For orbital geophysics the SAR experiment is
the major thrust, providing a first exploration of the uppermost few
meters of regolith and mantling materials, and topographic change
detection over broad regions. The landed package addresses interior
structure objectives that have been a high priority for "next steps" in
multiple MEPAG and NRC reports. The addition of capable spectroscopy for
composition rounded out the high-priority surface science envisioned by
the SAG-2. Continued climate monitoring is provided by a wide-angle
imager as well as the SWIR/TIR experiment, and the landed package
includes a meteorology station.

There is excellent scientific synergy among the elements of Plan G. For
example, a seismometer might detect a new impact event and provide some
information on its location, the wide-angle visible imaging and
medium-angle thermal imaging can be acquired to find small changes in
albedo or temperature, the HCI can verify if it was indeed an impact
event and determine the number and dispersion of craters, and SAR can
characterize the subsurface properties and topographic changes.

Atmospheric and polar sciences receive less emphasis in Plan G than in
Plans A or P, respectively. The wide-angle imager and SWIR/TIR
instruments and the landed met package do satisfy some of the
atmospheric science goals, and provide support to future missions. The
desire for a changing time of day provides unique atmospheric science
opportunities compared to recent missions with similar payload assets.
The changing time of day could be accomplished with an orbit that is
nearly polar, such at 85º, so there would be excellent opportunities to
observe the polar terrains with imaging, SAR, and SWIR/TIR, but Plan G
lacks the Laser Altimeter. An 85º inclination orbit would also be useful
for solar occultations via FTIR to search for trace gasses and to see if
spatial and/or temporal variability exists. If such variability does
exist, then the characterization possible in Plan G would be inferior to
that of Plan A, given less complete seasonal coverage as a function of
geography (function of orbit inclination) and lack of a sub-mm
spectroscopy experiment for dynamics.

The reduced Plan G descopes the landed package and replaces the SWIR/TIR
with a less capable TIR experiment while preserving the highest priority
observations for geology, landing sites, and orbital geophysics. An
alternate reduction would be to keep the landed package while
eliminating or reducing orbital payload elements.

Plan G will provide significant feed forward to several possible future
Mars exploration scenarios. The combination of HCI and SAR will provide
excellent characterization of candidate landing sites for an
Astrobiology Field Lab, mid-range rovers, Mars Sample Return, and
potential human exploration. In addition the SAR provides subsurface
information relevant to potential shallow drilling. The landed package
could be a critical precursor for a network landed mission, providing a
first station or baseline for a long-lived network or at least a proof
of concept. In other words Plan G provides excellent support for all the
future exploration pathways described in NASA's 2006 "Robotic Mars
Exploration Strategy 2007-2016."

## International Cooperation

There may be significant opportunities for international cooperation
with MSO either through foreign instrument or instrument subsystem
contributions or participation by international scientists as members of
proposed instrument teams. Several space agencies are working on
missions to Mars, including the 2013 ExoMars missions by the European
Space Agency. Since the ExoMars mission may not be able to carry the
entire payload that has been proposed by the different national
agencies, there may be a possibility for those payloads to be embarked
onboard a NASA mission if they fulfill the scientific requirements. The
SAG-2 encourages that the AO be written in a way that invites such
contributions to all candidate payload elements. Both instrument and
team members contributed from international sources should be competed
as part of the AO process, not simply "negotiated".

9.  []{#__RefHeading___Toc42082119 .anchor}MSO Project Analysis

## Mission Design Summary

Concurrent with the SAG-1 and the SAG-2 studies, a JPL group of mission
design experts studied the trade space for the MSO mission, in order to
gain a notional estimate of technical and resource requirements. Initial
assumptions were that the spacecraft should be a MRO-class spacecraft,
launched in 2013 and staying in Mars' orbit for about 10 years, with a
mission cost similar to the MRO costs.

The mission is to carry a science payload, the nature of which is to be
explored by the SAG-2 and a post -- SAG-2 Science Definition Team.
Further, MSO is to carry a capable telecommunications payload to
replenish Mars' relay infrastructure as existing assets phase out,
ensuring robust relay support for the 2nd decade of exploration. With
its telecommunications capability, MSO will also provide critical events
coverage, to monitor the arrival and landing of future spacecraft. To
this end, fuel will be carried to provide several inclination changes (≈
1˚ each) to slowly walk the orbit plane to the proper alignment each
time. Approximately 60 m/s of delta-v is required for a 1˚ inclination
change.

![](media/image3.pct){width="3.286111111111111in"
height="3.7819444444444446in"}

The mission design parameters are:

-   Trajectory: Type II

-   C3: 11.3 km/s2

-   Launch: November 21, 2013

-   Arrival: September 17, 2014

The mission scenario:

-   MOI: 300 x 34,000 km orbit

-   Inclination: 82.5˚ (TBD; see discussion in Mission Design trades
    below)

-   Aerobrake: ≈ 6-9 months

The ten-year on orbit time would be divided into an approximately
three-year "Science Emphasis" period (yellow orbit), and a seven-year
"Telecom Relay Emphasis" period (green orbit). The science orbit would
be at 300 km altitude (actually 270 x 330 km), and the relay period at
400 km (actually 370 x 430 km). The target launch vehicle is an Atlas V
4x1/5x1 series, with a 3,510 kg payload capability.

## Key Spacecraft Configuration Options

Mission scenarios were considered by the MSO project that paralleled
concurrent SAG-2 deliberations. The project selected plans that would
bound the envelope of mass and cost from an early version of the mission
scenarios provided by the SAG-2. Plans A and P were considered to be
fiscally equivalent. The Project considered two cost levels. The nominal
level of "OS" has a cost guideline of \$100M and 160kg for science
payload. This corresponds to the "Reduced" version of Table 8. A higher
cost level "FSO+" has a cost guideline of \$160M and 250kg for the
science payload. This is consistent with the Core Mission Concepts and
with some of the "Augmented" plans in Table 8. To demonstrate the effect
of including a network lander (NL) to the mission, the MSO team added a
lander element to its OS option. The accommodation of a landed payload
was not done in detail, but only as an "existence proof" model. This
analysis showed that MSO can accommodate 2-3 major science thrusts in
addition to its telecommunications relay function. The spacecraft
configuration was also notional. Detailed design requirements will
follow a specific science theme. Table 9.2 describes spacecraft
characteristic for the "OS" version. Subsequent columns reflect the
change in technical parameters required to accommodate a more complex
payload. For the "FSO+" payload, the entire spacecraft becomes more
complex, primarily to accommodate both the HCI and the SAR. However, for
the addition of a lander to the "OS" option, the impact on the
spacecraft is mostly in the mass accommodation and increased I&T
support.

**Table 9.2 Spacecraft Configuration**

![](media/image4.jpeg){width="6.25in" height="2.85in"}

The currently considered operational scenario assumes a "turn to Earth
downlink" strategy to reorient the spacecraft to communication with the
DSN. This strategy avoids the risk/cost/mass penalties for precision
pointing of a large gimbaled antenna with outboard Ka-Band amplifiers.

The network lander (the single pathfinder) studied was taken as a "black
box" originating from several studies done in the recent past of rough
and hard landers, and actually flown systems. This limits the option
space to impact velocities greater than 10 m/s and acceleration from a
few hundred to \~2000 g. The mass ejected from the orbiter prior to the
MOI is of the order of 200 kg, including mass margins, which includes a
landed payload of the order of 5 kg. The total notional costs of the
network landers considered by the MSO team were of the order of \$200 M
which includes the accommodation on the spacecraft and the mission,
landed payload, and reserves. The notional estimates of the landed
payload cost included in the total are of the order of \$10 M.

The following figure depicts a notional configuration for the
spacecraft, assuming the Mission Scenario Plan A. From the "Reduced"
version paths to accommodate the HCI, SAR or landed science are shown.

![](media/image5.jpeg){width="6.4in" height="4.8in"}

## Mission Design Trades

The MSO orbit will be near-polar, with \~ 80˚ to 95˚ inclination. A high
inclination orbit allows access to the entire planet. However, the
precise inclination desired by individual instruments depends on their
viewing requirement. Typically, nadir-pointing instruments prefer polar
inclinations (≈ 90˚), while others, particularly the solar occultation
FTIR needs to be at lower inclination as described in Section 8.

The inclination for a sun-synchronous orbit is 92.6˚ at 300 km altitude,
and 92.9˚ at 400 km altitude. The Local Mean Solar Times (LMST) can be
chosen, such as the 3pm -- 3am MRO orbit (although not all LMSTs will be
possible). The sun-synchronous orbit has benefits, such as increased
thermal stability of science instruments, reduction of thermal impact on
the spacecraft and its operation, and favorable conditions for detector
cooling. However, in addition to instruments desiring observations at
varying LMSTs, non sun-synchronous orbit inclinations are required for
critical events coverage.

### Solar Occultations Study

In order to be able to compare orbital requirements of solar occultation
instruments to others, a brief study was undertaken to outline the
sensitivity to inclination and altitude. The limb occultation geometry
is depicted below.

![](media/image6.png){width="6.389583333333333in" height="3.0in"}

An occultation is defined as the passage of the line of sight from the
S/C to the Sun passing through the atmosphere at the limb of Mars as
seen from the S/C over a range of altitudes from 0 km to 100 km (for a
Sunrise event; reverse direction for a Sunset event).

The parameters of interest are:

-   Latitude of Atmosphere at the Limb at 0-km altitude for all
    occultations - plotted chronologically

-   Latitude vs. Longitude of Atmosphere at the Limb at 0-km altitude
    for all occultations

-   Duration of all occultations - plotted chronologically

-   Projected Distance on Mars Surface of the separation of the
    locations of the atmosphere at the limb for 0 km alt. and 100 km
    alt. for all occultations - plotted chronologically.

-   Local Mean Solar Time of Orbit Node plotted chronologically for 1
    Martian Year

-   Longitude of the Sun (Ls)

The required observing conditions: Limb crossing durations \> 50 s with
projected ground distances \< 1000 km.

The parameters were determined for an MSO in a quasi-circular ("frozen")
orbit at altitude 273 x 327 km, with non sun-synchronous inclinations of
74°, 80°, 82.5°, 85°, 87.5°, plus a sun-synchronous inclination of
92.6°.

The results of study for 74° inclination (optimal for occultation
opportunities) are plotted below, in terms of latitude at the limb and
latitude vs. longitude coverage. In this orbit a wide range of latitudes
is visited repeatedly, from season to season. Such repetitive coverage
is desirable for atmospheric signatures measurements, as described under
Mission Scenarios in Section 8.1.

*Inclination 74˚*

![](media/image7.png){width="4.444444444444445in"
height="3.5555555555555554in"}

![](media/image8.png){width="4.444444444444445in"
height="3.5555555555555554in"}

*Inclination 85˚:* An orbital inclination between sun-synchronous and
74˚, for example 85˚, represents a compromise that may be acceptable for
the solar occultation, the nadir pointing instrumentation, and the
spacecraft thermal considerations. This example was considered for Plan
G, Section 8.3.

> ![](media/image9.png){width="3.807638888888889in"
> height="3.3340277777777776in"}

*Inclination 92.6˚ (Sun-Synchronous):* While desirable from an
operational point of view (e.g., thermal), a sun-synchronous inclination
does not provide any latitude coverage near the equator for
occultation-based measurements during any one season, and is therefore
an undesirable orbit from the point of view of trace gas measurements.

![](media/image10.png){width="4.166666666666667in"
height="3.3333333333333335in"}

### Lander Accessibility

The region of accessibility to a lander depends very strongly on the
particular launch dates and arrival dates, as well the entry
characteristics (entry speed, entry flight path angle, atmospheric
descent phase) of the lander itself. For the current baseline launch
period, which is optimized for mass deliverable into Mars orbit, and for
entry characteristics similar to MSL\'s we would have a maximum northern
latitude of 30˚, maximum southern latitude of 85˚, and an inertial entry
speed of 5.9 km/s.

If, for example, accessibility is an important factor outside of this
region, or if this entry speed is too high for particular technologies,
then further mission design work is required and could significantly
affect the mass performance and the appropriate launch vehicle, amongst
other factors.

## MSO Implementation

Notional science payload costs for the "OS", "FSO+", and "OS+NL" options
were estimated by the MSO project using the following assumptions:

-   The cost includes development and delivery of the flight instrument
    (Phase A-D, No Phase E)

-   The costs are in constant FY06 \$s

-   No \$ reserves are included (Project holds 30%)

-   The costs do not include science management and the office of the
    Project Scientist

The cost estimate of the "OS" option is consistent with an MRO-class
mission. "FSO+" and "OS+NL" are consistent with possible budget
augmentations being discussed with HQ. The "OS" science payload is
estimated notionally at \$110 M. The "FSO+" and "OS+NL" are of the order
of \$180 M, and \$190 M, respectively. The "OS+NL" payload cost estimate
includes not only the cost of the landed science payload but also the
total cost of the drop-off-package that is jettisoned prior to the MOI.
As noted, no reserves are included in these costs. Depending on the
specific design of the drop-off-package, a technology development
program may have to be initiated to advance the drop-off-package
technology readiness to level 6 by the Project PDR. These potential
technology development costs are not included.

The dry mass of the MSO flight system, consisting of the spacecraft and
science payload, was estimated at 1350 kg, 1650 kg, and 1600 kg for
options "OS", "FSO+", and "OS+NL", respectively. The mass margin
included in these mass estimates is 30% of the total allocation, or 43%
of the nominal current best estimate (CBE). The science payload masses
included in the totals are of the order of 170 kg for options "OS", 250
kg for "FSO+", and 370 kg for "OS+NL". All three options are within the
capability of the Atlas-V 4x1/5x1-class launch vehicles for the 2013
Mars launch opportunity. The "OS+NL" payload total consists of orbital
science payload of 170 kg plus a drop-off-package of 200 kg, which
includes approximately 5 kg of landed science. All payload masses
include contingency.

## Schedule

The MSO development schedule (below) supports an orderly approach to the
development of a planetary mission with competitively selected
instruments. The development phase durations and associated products are
based on NASA project management requirements and lessons learned from
recent planetary missions. The most important early schedule milestones
are the Instrument Announcement of Opportunity release in February 2008
and the Mission Concept Review in May 2008. Preparations for these key
milestones depend on timely determination of the mission science
objectives and conclusions of the Science Definition Team. The approach
is designed to minimize the risks inherent in the development cycle of
competitively selected instrumentation, in order to fulfill NASA\'s goal
to produce landmark science while staying within cost boundaries.

![](media/image11.pct){width="6.577083333333333in"
height="1.6388888888888888in"}

## Summary

In summary, mass and cost evaluation by the Project shows that all Core
Mission Concepts and "Reduced" SAG-2 Plans fit within the resources
range being considered by the Mars Program. The resources range in
science payload cost terms from MRO-class to MRO x 1.6. The SAG-2 "Plan
A Reduced" cost and instrument selection is similar to Project's
MRO-class Strawman, Option "OS". SAG-2 "Plan A Augmented " is similar to
Project's "FSO+" option, and included accommodation of a SAR. The
Project option "OS+NL" adds a simple lander system to the baseline "OS".
In cost terms this latter option is comparable to "FSO+"

10. []{#__RefHeading___Toc42082128 .anchor}Observations in Support of
    Future Exploration

## Landing Site Hazard Assessment

The SAG-2 was also requested to study major science drivers and
requirements for a camera system on MSO, with additional input on the
"programmatic" need for characterizing future landing site hazards. Much
of the first part of this analysis was included in the overall study of
scientific investigations above, where visible-wavelength images play a
significant role. The landing site issues were addressed through input
from members of the SAG-2 and others currently involved in the site
selection for Phoenix and MSL. At a broad level, the sub-group examined
three possible options for camera capability: 1-m/pixel resolution,
30-cm/pixel resolution similar to HiRISE, and a 5-10 cm/pixel capability
not yet demonstrated in Mars orbit. Landing hazard assessment has
changed dramatically based on 30-cm/pixel resolution rather than
1.5-m/pixel resolution images, as evidenced by the shift in Phoenix
landing sites after HiRISE imaging discovered numerous meter-scale
boulders in areas previously thought to be safe. Given current
requirements for landing safety (size of error ellipse and maximum scale
of tolerable rocks given EDL system capabilities), a 30-cm/pixel
capability for imaging future landing sites is well justified. There was
no consensus that 5-10 cm/pixel image resolution was required for
landing *safety*, though cogent arguments are presented above for the
scientific value of such observations.

The ability to re-image sites over a wide variety of illumination angles
enables significantly greater information and understanding of
small-scale features than imaging at the same resolution and SNR but
with a fixed local mean solar time (LMST).   This was studied and
simulated in detail for the Mars Rover Sample Return report on orbital
imaging requirements (Bourke, R. et al., 1989).   Alan Delamere (Ball
Aerospace) constructed a laboratory Mars model and imaged it under
variable illumination.   Steve Squyres selected the field sites and
photography and led that analysis.   One of their major conclusions was
that features near the resolution limit can be detected and understood
if imaged under multiple sun elevations and azimuths.  The Artificial
Intelligence community has developed what they call \"photometric
stereo\", in which 3 images of a scene with different illumination
geometries are used to extract albedo, slope, and strike of each pixel
(Wolff et al., 1992).  Geometric stereo derives topography for an area
of typically 4x4 or 5x5 pixels, so photometric stereo can provide
quantitative topographic data at 4-5 times higher planimetric resolution
from comparable image resolutions.  So significantly improved
characterization of key locations (candidate landing sites,
potentially-active gullies, etc.) is possible with a migrating LMST,
without the expense of a larger telescope.

In addition, current-generation analogue waveform-based laser altimeter
methods can facilitate few cm resolution vertical roughness measurements
across the scale of the measurement footprint; swath imaging lidar
altimeters have been demonstrated that facilitate direct (deterministic)
measurement of cm-scale vertical roughness across footprints in the 1 to
10m range, thereby adding significantly to what can be derived from
imaging alone. Such methods may be applicable for characterizing and
identifying safe landing zones on Mars for human exploration at scales
required for mid L/D-based landing flight systems. Instruments
considered in the trade space for MSO include multibeam lidar altimeters
with waveforms that facilitate measurement of 1-5cm scale vertical
roughness at the 10-20m footprint scale.

## Atmospheric Environment for Flight Aerodynamics

The utility of observation of the atmospheric environment has been
demonstrated with regard to aerobraking by MGS, ODY and MRO and with
regard to entry, descent and landing (EDL) by MER and in the planning
for PHX and MSL. Later landing or aerobraking systems, including
components of MSO itself, also require a proper characterization of
atmospheric environments likely to be encountered. Continued
characterization of the lower atmosphere will aid design and
implementation of EDL and precision landing for future landers and for
vehicles employing aerocapture or prolonged atmospheric passage,
including the much larger vehicles required for human exploration of
Mars. Early work on the latter has already highlighted the need for
atmospheric data bases because critical design issues must be addressed
in the coming decade for missions that will not launch until much later
(i.e., well after 2020).

Accelerometer measurements by MSO will be used in its aerobraking phase
and will provide additional data for characterizing the upper atmosphere
in a different combination of Mars year, season, and solar cycle. These
accelerometer measurements should be preserved as a scientific data set
and can then be used to improve models of upper atmosphere structure and
circulation, as these provide the means to extrapolate to times and
places not directly observed.

A key factor in the design, testing and actual EDL of landing spacecraft
has been wind and its variation in space and time. Typically, entry
vehicles have vulnerabilities that are sensitive to medium and
small-scale (mesoscale) features of the wind field. This is complicated
by the fact that near-surface winds are particularly sensitive to the
substantial influence of local topography. Given the virtual absence of
direct wind measurements on any scale, it has been necessary to depend
upon numerical models of the wind field and theoretical extrapolations
from these to scales (\<= 1 km) that remain unresolved even in these. It
is unlikely that, with the technology available today for flight to
Mars, wind can be measured directly with the precision and resolutions
required to support flight design and simulation. However, the direct
measurement of winds at larger scales, even at modest precisions (e.g.,
10 m/s averaged over 10-km layers), would provide a powerful constraint
on the models used to simulate the finer-scale features. These
measurements are most useful for validation when made in combination
with profile measurements of aerosols and temperature. Then both the
model drivers and the model response are independently constrained. MSO
could provide this capability.

While half-scale height vertical profiles of aerosols are sufficient to
provide improvement to our understanding of the forcing and responses in
the atmosphere, the multi-beam lidar would be a much more rich dataset
with which to explore the atmosphere\'s aerosol processes. Its ability
to yield aerosol profiles with 100m vertical and 1km horizontal
resolution from the surface to \~50km is well matched to both the scales
of the phenomena in the atmosphere, as well as the scales of the models.
In this way, the multi-beam lidar could provide significant constraints
to further tune the atmospheric models.

The landed meteorological instruments considered can also have a big
impact on the improvement of mesoscale and global models. These
instruments represent a new class of observations over previous landers
that would increase insight into, and provide validation of, the
physical parameterizations used in models calculating near-surface
fields. While the landed observations themselves are not globally
representative, a model that has been properly tuned using these data
can be more confidently applied across the globe. The result would be a
significant improvement in the fidelity of mesoscale models to predict
landing conditions.

Continuation of the weather monitoring, and of the temperature, dust and
water climatology for several more Mars years would significantly
increase the probability that the full range of environmental conditions
to be encountered would be captured, as Mars varies from year to year.
Finally, for those missions arriving while MSO is actively operating on
station, the temperature profilers and atmospheric monitors would
provide near-real-time observations of atmospheric state that would
permit updates to critical EDL or aeropass parameters, as was done for
MER and all the aerobraking orbiters.

## Precursor measurements for future human exploration

In 2005, NASA's MEP and MEPAG formed a subcommittee to examine precursor
measurements needed to reduce the risk of future human exploration
missions to Mars. This Mars Human Precursor Science Steering Group
(MHP-SSG), identified and prioritized these needed measurements. Many
MSO science measurements directly address these exploration program
needs. The table on the next page identifies the specific exploration
investigation as identified by the MHP-SSG and MSO's potential
corresponding complementary capability. We note that MSO could make
advancements in nearly every one of exploration's top priorities. Other
Exploration Systems Mission Directorate engineering needs are coupled to
flight system design trades associated with human access to Mars. These
are summarized below (and are not listed in the MHP-SSG table).

Additional knowledge requirements for human exploration of Mars (and of
the Moon) have been identified in recent ESMD engineering documents, as
derived from ESAS studies during 2005-2007. Ongoing design reference
mission studies by a Mars Architecture Working Group (2007) are
developing revised engineering knowledge requirements to facilitate
human missions to the Martian surface. Included in the set of evolving
requirements is the requirement for a global control network of ground
control points (all within a center-of-mass reference frame, aka
areocentric) to permit ALHAT algorithm development, testing and
certification for human landings. ALHAT is the set of procedures to
allow for precision, autonomous landings of human-rated flight systems
on Mars, as is under development at NASA's JSC (with Draper Labs) for
the human return to the Moon. Development of a global, center-of-mass
referenced topographic model (DEM) for Mars with sub-meter vertical
accuracy at horizontal scales (globally) of 100m or finer is a key
element of the ALHAT approach. Suggested MSO instruments could
facilitate development of this legacy dataset for both engineering of
human landings (and landing algorithms) as well as for regional-global
scale scientific investigations as summarized above. Finally, in situ
resources and ISRU capabilities are one variable under consideration by
ESMD engineers to enhance and facilitate human exploration of Mars. MSO
instruments could begin the process of resource identification and
localization via high-resolution studies of accessible water ice
deposits in regions where human exploration may be preferred for
scientific and safety reasons. MEPAG has sponsored a committee (HEM-SAG)
to examine science and related goals for human exploration as inputs to
the ESMD engineering process in 2007. Several issues associated with
localization and understanding in situ resources, and in particular
water ice concentrations within an accessible control volume, are under
discussion. MSO instruments such as high-resolution multi-polarization
SAR or high-resolution neutron spectrometers, as well as SWIR/TIR
mineral mapping can contribute to this goal.

  ------------------------------------ ----------------------------------
  Exploration Investigation (Beaty et  Complemented by MSO
  al., 2006)                           

  Characterize the particulates that   Atmospheric state sensing devices
  could be transported to mission      like Thermal-IR, and MARCI-like
  surfaces through the air             imagers will monitor density and
                                       flux of airborne dust activity
                                       over seasons; additional insights
                                       from the landed met package and
                                       the atmospheric lidar.

  Determine the variations of          The orbital atmospheric state
  atmospheric dynamical parameters     instruments, combined with the
  from ground to \>90 km that affect   landed met package represent a
  EDL and TAO                          nearly complete set of instruments
                                       to address this goal.

  Determine if each Martian site to be While a definitive measurement of
  visited by humans is free of         a highly bioloaded site would
  replicating biohazards               require a landed mission, some
                                       inferences might be obtained via
                                       the atmospheric signature
                                       packages, though more sensitivity
                                       may be required.

  Characterize potential sources of    Many elements of the MSO suite
  water to support ISRU for eventual   contribute to the determination of
  human missions.                      water sources, including MARCI,
                                       Thermal-IR, SWIR, Cameras, SAR.

  Determine the possible toxic effects While a sample return mission is
  of Martian dust on humans.           required to definitively determine
                                       the soil toxicity, trace gas
                                       instruments may infer the presence
                                       of harsher chemical species
                                       created by dust; advanced active
                                       systems could resolve species at
                                       km scales to isolate potential
                                       vents.

  Derive the basic measurements of     Electric field system on the MET
  atmospheric electricity that affects landed package will provide the
  TAO and human occupation.            first-ever assessment of Martian
                                       atmospheric electricity

  Determine the processes by which     While a definitive measurement of
  terrestrial microbial life, or its   a highly bioloaded site would
  remains, is dispersed and/or         require a landed mission, some
  destroyed on Mars                    inferences might be obtained via
                                       the atmospheric signature
                                       packages. More advanced active
                                       optical systems may be required.

  Characterize in detail the ionizing  N/A
  radiation environment at the Martian 
  surface,                             

  Determine traction/cohesion in       Thermal IR mineral mapping can
  Martian soil/regolith                determine the compositional nature
                                       of various regions, providing some
                                       inference on soil physical
                                       properties; multiple polarization
                                       surface lidar observations can
                                       constrain particles sizes and
                                       local slopes and roughness at 1-5
                                       cm scales. High-resolution (30
                                       cm/pixel) images can identify sand
                                       or dust deposits based on
                                       distinctive morphologies.

  Determine the meteorological         Landed MET can provide direct
  properties of dust storms at ground  insight into weather conditions at
  level that affect human occupation   ground during atmospherically
  and EVA.                             unstable periods.
  ------------------------------------ ----------------------------------

11. []{#__RefHeading___Toc42082132 .anchor}Discussion and Issues

## Science Issues

Despite extensive discussion and scientific wrangling, further reduction
of the three plans to one "highest priority" scenario was simply not
possible. Although there are overlaps, each of these three scenarios
pursues a different primary objective, with a different follow on to the
Mars Exploration Program in the years after 2013. The discussion below
captures several scientific issues and their resolution, where achieved.
In the end the SAG-2 membership has high confidence that any one of
these three scenarios will return significant and important and **new**
information relevant to our understanding of the planet, its history and
its potential for life, as described related to each plan in Section 8.

#  {#section .unnumbered}

### Subsurface Imaging

Concerns regarding the subsurface imaging investigation, and not
necessarily with how it is accomplished, center on whether a view below
the surface will be truly revealing, arguing that we can instead simply
infer the subsurface geomorphology over large areas from occasional
surface outcrops or from muted topographic signatures. The outcome of a
fundamentally new investigation cannot be fully predicted, but
terrestrial, lunar, and Martian subsurface probing to date strongly
suggest that significant insights will result.

### Methane detection and traceability

There was considerable discussion within the SAG-2 on two points: (1)
What is the value of an Atmospheric Signatures investigation if methane
is not detected? (2) If atmospheric measurements detect a trace gas
indicating ground geochemical or biogeochemical activity, can a surface
source be localized sufficiently well that a future mission can
follow-up on that discovery?

With regard to the first question, the proposed measurement requirement
would establish whether atmospheric methane was present at levels far
below what has been reported to date or can be detected in the future
(e.g., by MSL). This will remove any ambiguity of the reported
discovery. However, the more important point is that active subsurface
processes could have atmospheric signatures other than methane, so that
it is a suite of trace gases that is targeted. Furthermore, it will be
their relative abundances that help discriminate between the processes
that produced them and that indicate, by analogy with Earth, if their
source is more likely to be biochemical or geochemical in nature.

The second question---could one find a local source if it existed---was
also debated among the SAG-2 members. The ideal would be to locate a
source area with sufficient precision that it fits inside a precision
landing ellipse (e.g., \<10 km diameter circle) for a successor mission.
This is not likely to be achieved given the rapid mixing in the Martian
boundary layer and the rapidity of redistribution by the general
circulation, even for signature species with a relatively short
atmospheric lifetime. However, there is a strategy in which progress can
be made in localizing the source, within the range of instrument
resources considered by the SAG-2 to be practical for an MSO payload.

This strategy was captured in Scenario A: 1) Choose an instrument (e.g.,
the FTIR) with the sensitivity to detect a suite of trace gases (the
atmospheric signatures), 2) Map (e.g., with the sub-mm spectrometer) a
select few trace gases with denser coverage (but typically less
precision) than solar occultation measurements can provide, 3) Observe
winds, temperature and dust opacity in order to validate and drive
transport models that can do the final tracing to more localized areas,
and 4) Image the surface of these potential source regions to further
isolate likely points or locales of origin.

### Higher Spatial Resolution than HiRISE

The SAG-2 discussed the scientific return from imaging at significantly
better spatial resolution (and comparable signal-to-noise ratio) than
HiRISE (30 cm/pixel at 300 km altitude). This resolution can help
resolve fundamental issues with regard to active processes such as
gullies, and provides imaging at the equivalent of lander scales at many
more sites than we will be able to land at during the coming decade.
State of the art visualization can effectively show the surface view in
these extreme high-resolution views. Similar techniques are actively
being used for navigation of MER from HiRISE images. Unfortunately,
achieving spatial resolution of 5-10 cm, under current state of the art,
increases both mass and cost significantly, and largely becomes the only
scientific goal for MSO. Also, spacecraft stability could become the
limiting factor in resolution rather than the telescope. We discussed
the possibility of "shared optics" i.e. a view similar to the space
telescope where a single optic is shared by multiple instruments, but
the practicalities of creating multiple optical chains were seen as
prohibitive for the MSO mission. Though discussed at multiple stages in
the process, the majority did not condone a "single instrument" core
mission and so this option was ultimately dropped.

### Seismic detection.

Concerns were expressed that the landed geophysics, in particular the
search for seismic events might not result in a detection. It is
recognized that expected number of detections goes down (and the risk of
non-detection goes up) with just one landed package, and there is
geometric growth in return with each station added. There has been a
great deal of published work to estimate the expected rates of events
from the cooling rate and predicts of seismic energy released, from
historical faulting rates, and from extrapolating between the observed
activity on the Moon and Earth. Based on these various approaches all
agree that we should expect a few dozen globally detectable quakes/year
(+/- an order of magnitude), with a reasonable expectation of many more
regional and local events (assuming a seismometer with the sensitivity
described in Table 6.4). The recently discovered MGS-era impact features
provide direct evidence for \~10-20 significant seismic events per year.
The Viking negative result is consistent with these estimated rates
given the sensitivity of that seismometer and its duty cycle, as
described in section 6.4.2.

The SAG-2 discussed whether a single drop package would remove the
impetus to have a long-lived network for landed geophysics. The
consensus is that in order to justify a full network mission a single
measurement may actually be needed to provide better justification. If
there really were a lack of results then the need for further
measurements would indeed be questionable. A low rate of observed
activity would require tough decisions about the value of future landed
measurements.

### Landed Science Priority

There was considerable discussion about how to best use the payload mass
likely to be landed as a drop-off package from MSO \[see also 11.2.1
below\]. This resulted in a clear prioritization of the geophysics
package instruments as follows: Seismometer, ranging for geodynamics,
heat flow experiment. \[The case for the seismic measurements was
further discussed above in 11.1.4.\] Prioritization between this
geophysics package and an integrated meteorological package was more
difficult. Comprehensive meteorological studies require data acquired
from multiple stations dispersed over a wide variety of terrains.
However, given the lack of detailed boundary layer measurements from
anywhere on Mars, a single station would still provide a key data set
for validating atmospheric models and their treatment (or resolution) of
critical boundary layer phenomena. Such a station could also provide
ground-level atmospheric truth for remote sensing observations (as in an
augmented Plan A---see Table 8). The geophysics package gained a
preference in that it begins to fill an enormous gap in our knowledge
about Mars and its results are likely to have a more profound effect on
a future landed network. However, the return from an integrated
meteorological package was judged to be so significant that the SAG
supported its inclusion.

### Neutron spectroscopy

Very late in the process a discussion of improved neutron spectroscopy
emerged. Within the context of measurements that support the climate and
polar processes theme (Plan P), high resolution neutron spectroscopy
(HRNS) offers a means for mapping spatial variations in hydrogen (H)
content within the polar regolith down to approximately one meter depths
at perhaps 80-100 km scales, relative to the existing ODYSSEY 500km
resolution observations. A higher resolution neutron spectrometer can
observe the seasonally changing column densities of the seasonal ice cap
at a higher spatial resolution, providing details about smaller features
such as the Mountains of Mitchell or the amount of seasonal CO~2~ ice
that accumulates above the south polar residual cap. When combined with
LIDAR measurements, regional CO~2~ densities can be derived as a
function of season, thus providing information about CO~2~ formation and
densification processes. Neutron spectroscopy can also be used to track
the amount of inert gases in the atmosphere. In light of these issues,
an augmented Plan P could include neutron spectroscopy as an alternative
to SAR, but SAG-2 did not have time to deliberate this change.

## Technical/Cost Issues

### Trades Involving a Landed Drop Package

In the absence of a defined architecture for the delivery of the
drop-package, the SAG-2 could not weigh cost-benefits of the landed
package versus the orbiter package. The SAG-2 did feel that a
significant payload of remote sensing instruments addressing one or more
of the themes articulated in this report should be a defining attribute
of an MSO mission; that is, the orbiter should be much more than just a
carrier for the telecommunications and drop-package systems. This was
consistent with the SAG-2's belief that no one "instrument package"
should dominate the MSO mission. As the scenarios above attest, the
SAG-2 felt the drop-package would produce significant and substantial
science, particularly in combination with particular orbiter payloads.
But there will be costs that the SAG-2 was not in a position to
consider.

The other concern with regard to the landed package was whether the
landed mass (projected as \~ 5 kg) would be enough to do a meaningful
geophysical payload, let alone one combined with an integrated
meteorological package. The payload must include a capable seismometer
with an X-band transponder needed for geodynamical ranging as a close
second in priority. While even a single high-precision pressure sensor
would return valuable data, the integrated meteorological package is
needed to provide new insights, not only for the fundamental atmospheric
science at Mars, but also for landing safety considerations of future
missions as well. Increasing the landed capability to \~10 kg would
significantly enhance the scientific return of the drop-package, more
fully justifying the cost of its inclusion in the mission.

### Budget Reserves

By design, each of the scenarios presented above include new
measurements for Mars. Although an "existence proof" is indeed available
for each one of the new capabilities, adaptation to flight on a Mars
spacecraft may well entail considerable development. Thus, a now
traditional payload reserve margin of \~30% may not be adequate,
depending upon the number of innovative instruments and the desire to
extend capabilities even of previous Mars instruments. The SAG-2
suggests that the Science Definition Team take a careful look at the
capabilities to be requested in the future AO for MSO and scope the
reserve accordingly.

### Funding of Science Activities during Development (Phases A-D) 

Science team activities during Phases A-D would include: 1) conduct
critical pre-flight instrument calibration and testing, 2) prepare for
safe commanding of the instrument and monitoring of its health after
launch, and 3) prepare the ground data systems needed to further
calibrate and operate the instrument once it is in orbit around Mars and
4) to analyze the data acquired. It was not clear to the SAG-2 whether
these development phase science costs have been included appropriately.
One safeguard is to ensure that the instrument development costs do not
overrun (see 11.2.2 above) and eat into these preparation costs. The
Science Definition Team should estimate these costs based on the
capabilities required and the complexity and desired schedule of product
delivery.

12. []{#__RefHeading___Toc42082144 .anchor}Conclusion

The exploration of Mars is in the midst of a scientific revolution
brought forth by a major commitment by NASA to a sustained Mars
Exploration Program (MEP) with a high flight-rate and a continuous flow
of remarkable data. In spite of this major investment, Mars remains an
enigma, with diverse scientific \"gaps\" that remain in the era beyond
MRO and other missions. To think that the science that can be achieved
via orbital remote sensing is all but over is now viewed as folly.
Thanks to the ongoing MEP, we can describe several essential lines of
scientific strategy that must be evaluated as the keystones for a 2013
MSO mission. There is no one \"answer\" to what must be accomplished by
a 2013 MSO mission, in part because of the complexity of the Mars
\"system\" that deserves investigation. Simple questions about sources
and sinks of volatile species that could be tied to the history of
biology on the planet cannot be addressed, nor can the intricate
workings of the modern climate cycles reflected in the polar regions be
quantitatively described. Furthermore, there remain basic unknowns about
the state of the interior and the hidden landscapes of the most recent
geologic era, buried as they are by the ever-shifting deposits of dust
and recycled volatiles.

Because of these profound and basic unknowns, the MEPAG-chartered MSO
SAG-2 has developed a set of parallel pathways as potential lines of
scientific focus for a major step forward in the reconnaissance of the
Mars \"system\" in 2013. Each overlaps the other in distinctive ways,
and hybrid missions could certainly be developed. However, each pathway
emphasizes an essential line of scientific investigation that addresses
a set of connected unknowns.

For example, one \"pathway\" focuses on a broad, planet wide inventory
of diagnostic disequilibrium trace gases and aspects of the dynamics of
the atmosphere that controls their spatial and temporal distribution. A
second MSO \"pathway\" focuses attention on the energy and mass balance
of the dynamic polar regions (and associated volatile reservoirs) of
Mars, with attention to the fine-scale workings of surface processes. A
final pathway emphasizes the state of the shallow (and deeper) interior
as well as the geological signatures of past eras hidden by mantles of
covering materials across the entire planet. Each pathway continues
forward the capability to assess the safety and scientific worthiness of
future landing sites.

A scientifically bold reconnaissance in 2013 will set the course for the
MEP to cost-effectively target missions that must be accomplished
starting in 2016 and on into the 2020\'s. That no single mission
instrument complement addresses all of the largest knowledge gaps is not
surprising. The same situation is faced in Earth science, for which the
recently released NRC Earth Science Decadal Survey highlights 14 orbital
reconnaissance missions needed to understand the Earth\'s dynamic
systems. Why should Mars be any different?

[]{#__RefHeading___Toc42082145 .anchor}References

Beaty, D.W., Snook, K., Allen, C.C., Eppler, D., Farrell, W.M.,
Heldmann, J., Metzger, P., Peach, L., Wagner, S.A., and Zeitlin, C.,
(2005). An Analysis of the Precursor Measurements of Mars Needed to
Reduce the Risk of the First Human Missions to Mars. Unpublished white
paper, 77 p, posted June, 2005 by the Mars Exploration Program Analysis
Group (MEPAG) at <http://mepag.jpl.nasa.gov/reports/index.html>.

Bourke, R., et al. (Eds.), 1989, Mars Rover Sample Return Mission:
Report of the Mini-Workshop on Orbital Imaging Requirements.  JPL
D-6442, 40 pp. 

MEPAG (2006), Mars Scientific Goals, Objectives, Investigations, and
Priorities: 2006, J. Grant, ed., 31 p. white paper posted February, 2006
by the Mars Exploration Program Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>.

MAPG (2006): Mars Advance Planning Group, 2006 Update to "Robotic Mars
Exploration Strategy 2007-2016," Unpublished white paper, 24 p, posted
Nov. 2006 by the Mars Exploration Program Analysis Group (MEPAG) at
http://mepag.jpl.nasa.gov/reports/index.html

NRC (2003), New Frontiers in the Solar System: An Integrated Exploration
Strategy.

 

Wolff, L.B., S.A. Shafer, and G.E. Healey (eds.) 1992, Physics-Based
Vision: Shape Recovery, Jones and Bartlett, Boston, 522 pp. 

[]{#__RefHeading___Toc42082146 .anchor}List of Acronyms

Acronym Definition

ACE Atmospheric Chemistry Explorer

AFL Astrobiology Field Laboratory

AIRSAR Airborne Synthetic Aperture Radar

ALHAT Autonomous Landing and Hazard Avoidance Technology

AO Announcement of Opportunity

ASTER Advanced Spaceborne Thermal Emission & Reflection Radiometer

CALIPSO Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observation

CBE Current Best Estimate

CMC Core Mission Concept

COMPLEX Committee on Planetary and Lunar Exploration

CRISM Compact Reconnaissance Imaging Spectrometer for Mars

CTX Context Imager

DEM Digital Elevation Model

DOP Drop Off Package

DSN Deep Space Network

DTM Digital Terrain Model

ECHOS Electrical Charging Hazards Originating from the Surface

EDL Entry, Descent, and Landing

ESAS Exploration Systems Architecture Study

ESMD Exploration Systems Mission Directorate

EVA Extravehicular Activity

FTIR Fourier Transform Infrared

GCM General Circulation Model

GRS Gamma Ray Spectrometer

HCI HiRISE Class Imager

HEM-SAG Human Exploration for Mars Science Analysis Group

HiRISE High Resolution Imaging Science Experiment

HQ Headquarters

HRNS High Resolution Neutron Spectroscopy

InSAR Interferometric Synthetic Aperture Radar

IR Infrared

ISRU In Situ Resource Utilization

I&T Integration and Test

ITAR International Traffic in Arms Regulations

JPL Jet Propulsion Laboratory

JSC Johnson Space Center

LIDAR Light Detection and Ranging

LMST Local Mean Solar Time

LOD Length of Day

LOLA Lunar Orbiter Laser Altimeter

Ls Longitude of the Sun

MAPG Mars Advanced Planning Group

MARCI Mars Color Imager

MARSIS Mars Advanced Radar for Subsurface and Ionospheric Sounding

MATADOR Mars Atmosphere and Dust in the Optical and Radio

MATMOS Mars Atmospheric Trace Molecule Spectroscopy Experiment

MAVEN Mars Atmosphere and Volatile Evolution

MCS Mars Climate Sounder

MET Meteorology

MEP Mars Exploration Program

MEPAG Mars Exploration Program Analysis Group

MER Mars Exploration Rover Mission

MEX Mars Express Mission

MGS Mars Global Surveyor

MHP-SSG Mars Human Precursor Science Steering Group

ML3N Mars Long-Lived Lander Network

MOC Mars Orbiter Camera

MOLA Mars Orbiter Laser Altimeter

MOI Mars Orbit Insertion

MPF Mars Pathfinder Mission

MSL Mars Science Laboratory

MRO Mars Reconnaissance Orbiter

MSO Mars Science Orbiter

MSR Mars Sample Return

NASA National Aeronautics and Space Administration

NIR Near Infrared

NL Network Lander

NPLD North Polar Layered Deposits

NRC National Research Council

ODY Mars Odyssey Mission

OMEGA Observatoire pour la Minéralogie, l\'Eau, les Glaces, et
l\'Activité

PDR Preliminary Design Review

PHX Phoenix Mars Mission

P/L Payload

PLD Polar Layered Deposits

POP Program Operating Plan

REMS Rover Environmental Monitoring Station

RMS Root Mean Square

RSE Radio Science Experiment

ROM Rough Order of Magnitude

SAG Science Analysis Group

SAR Synthetic Aperture Radar

S/C Spacecraft

SDT Science Definition Team

SHARAD Shallow Subsurface Radar

SNR Signal to Noise Ratio

SPRC South Polar Residual Cap

SWIR Short Wave Infrared

TAO Takeoff, Ascent, and Orbit

TES Thermal Emission Spectrometer

TGE The Great Escape

THEMIS Thermal Emission Imaging System

TIR Thermal Infrared

TRL Technology Readiness Level

UHF Ultra-High Frequency

USO Ultra-stable Oscillator

VHF Very High Frequency