**Mars Science Goals, Objectives,**

**Investigations, and Priorities: 2008**

**Mars Exploration Program Analysis Group (MEPAG)**

**September 15, 2008**

**Prepared by the MEPAG Goals Committee:**

Jeffrey R. Johnson, Chair, United States Geological Survey
([jrjohnson@usgs.gov]{.underline})

*[Representing Goal I]{.underline}*

Jan Amend, Washington University (<amend@levee.wustl.edu>)

Andrew Steele, Carnegie Institute of Washington (<steelie@mac.com>)

*[Representing Goal II]{.underline}*

Steve Bougher, University of Michigan
([bougher@engin.umich.edu]{.underline})

Scot Rafkin, Southwest Research Institute
([rafkin@boulder.swri.edu]{.underline})

Paul Withers, Boston University ([withers@bu.edu]{.underline})

*[Representing Goal III]{.underline}*

Jeffrey Plescia, Applied Physics Laboratory
([jeffrey.plescia@jhuapl.edu]{.underline})

Victoria Hamilton, Southwest Research Institute
([hamilton@boulder.swri.edu]{.underline})

*[Representing Goal IV]{.underline}*

Abhi Tripathi, Johnson Space Center
([abhishek.b.tripathi@nasa.gov]{.underline})

Jennifer Heldmann, Ames Research Center (<jheldmann@mail.arc,nasa,gov>)

[Recommended bibliographic citation:]{.underline}

MEPAG (2008), Mars Scientific Goals, Objectives, Investigations, and
Priorities: 2008, J.R. Johnson, ed., 37 p. white paper posted September,
2008 by the Mars Exploration Program Analysis Group (MEPAG) at
http://mepag.jpl.nasa.gov/reports/index.html.

TABLE OF CONTENTS

Preamble 3

I. [GOAL: DETERMINE IF LIFE EVER AROSE ON MARS]{.underline} 6

> *A. Objective: Assess the past and present habitability of Mars* 6
>
> *B. Objective: Characterize Carbon Cycling in its Geochemical Context*
> 8
>
> *C. Objective: Assess whether life is or was present on Mars* 11

[II. GOAL: UNDERSTANDING THE PROCESSES AND HISTORY OF\
CLIMATE ON MARS]{.underline} 13

> *A. Objective: Characterize Mars' Atmosphere, Present Climate,\
> and Climate Processes* 13
>
> *B. Objective: Characterize Mars' Ancient Climate and Climate
> Processes\
> Through Study of the Geologic and Volatile Record of Climate Change*
> 16
>
> *C. Objective: Polar, Glacial and Periglacial Processes* 17

[III. GOAL: DETERMINE THE EVOLUTION OF THE SURFACE AND\
INTERIOR OF MARS]{.underline} 19

> *A. Objective: Determine the nature and evolution of the geologic
> processes\
> that have created and modified the Martian crust* 19
>
> *B. Objective: Characterize the structure, composition, dynamics,\
> and evolution of Mars' interior* 22
>
> *C. Objective: Understand the origin, evolution, composition and
> structure of\
> Phobos and Deimos.* 23

#### [IV. GOAL: PREPARE FOR HUMAN EXPLORATION]{.underline} 24

> *Objective A: Obtain knowledge of Mars sufficient to design and
> implement a\
> human mission with acceptable cost, risk and performance* 24
>
> *Objective B: Conduct risk and/or cost reduction technology and
> infrastructure\
> demonstrations in transit to, at, or on the surface of Mars* 31
>
> *Objective C: Characterize the State and Processes of the\
> Martian Atmosphere of Critical Importance for the Safe Operation of
> Spacecraft* 35

#### [V. CROSS-CUTTING STRATEGIES]{.underline} 37 

PREAMBLE

In 2000, the Mars Exploration Program Analysis Group (MEPAG) was asked
by NASA to work with the science community to establish consensus
priorities for the future scientific exploration of Mars. Those
discussions and analyses resulted in a report entitled *Scientific
Goals, Objectives, Investigations, and Priorities*, which is informally
referred to as the "Goals Document" (MEPAG 2001[^1]). The initial report
proved to be very useful for guiding program implementation decisions.
It also has become clear over the past few years that the report
requires regular updates in light of new results from Mars and changes
in the strategic direction of NASA. For this reason, MEPAG periodically
revises the Goals Document (MEPAG, 2004[^2]; MEPAG, 2005^3^; MEPAG,
2006^4^; MEPAG 2008-this document). As was the case with previous
versions, the Goals Document is presented as a statement of community
consensus positions.

The MEPAG Goals Document is organized into a four-tiered hierarchy:
goals, objectives, investigations, and measurements. The goals have a
very long-range character and are organized around major areas of
scientific knowledge and highlight the overarching objectives of the
Mars Exploration Program (Arvidson *et al*., 2006^5^). Expanded
statements of these goals are found in the report, but they are commonly
referred to as Life, Climate, Geology, and Preparation for Human
Exploration. Developing a comprehensive understanding of Mars as a
system requires making progress in all three sciences areas, while the
goal of preparing for human exploration is different in nature. Thus,
MEPAG has not attempted to prioritize among the four goals. A general
theme of understanding whether or not habitable zones and life have
existed, or do exist, on Mars has emerged within the framework of
understand Mars and all its elements\-\--interior, surface, and
atmosphere---as a highly interactive and complex system. However, some
of the fundamental science questions included in each goal may address
the evolution of Mars as a planet more directly than habitability.
Nonetheless, answers to those fundamental questions affect our analysis
of habitability issues and ultimately improve the effectiveness of the
Mars Exploration Program.

Each Goal includes two or three objectives that embody the strategies
and milestones needed to achieve the Goal. Objectives are presented in
priority order, because there is often an order within which the
scientific questions can most logically be answered, and/or some
objectives are perceived to be more important than others. In the
present version of the Goals Document, there are a total of 12
objectives, nine of which are scientific in nature, and three of which
relate to reducing the risk of mission operations.

A series of investigations that collectively would achieve each
objective is also identified. While some investigations can be achieved
with a single measurement, others will require a suite of measurement
types conducted across multiple missions. Each set of investigations is
independently prioritized for each objective.

Measurements constitute the fourth tier of the hierarchy. Measurements
are made by instruments that can be built and flown to Mars. MEPAG has
only considered scientific objectives that are amenable to measurements
(i.e., theoretical modeling, laboratory analysis, telescopic
observations are not considered). As measurement capabilities and
techniques evolve, detailed measurement requirements should be defined
by Principal Investigators, Science Definition Teams, and Payload
Science Integration Groups for program missions and by the Principal
Investigator and Science Teams for Scout missions. These requirements
can then contribute to program planning. An important exception to this
strategy, however, is the measurement set associated with Goal IV
Objective A, which relates to environmental data sets necessary to
reduce the risk of future human missions to acceptable levels. In that
case, a clear criterion exists (degree of impact on risk reduction) that
enables those measurements to be listed in priority order.

Completion of all the cited investigations will require decades and it
is possible that many investigations are so complex that they may never
be truly completed. Thus, evaluations of prospective missions and
instruments should be based on how well the investigations are addressed
and how much progress might be achieved in that context. While
priorities should influence which investigations are conducted first,
they should not necessarily be done serially, except where it is noted
that one investigation should be completed first. In such cases, the
investigation that should be done first was given a higher priority,
even where it is believed that a subsequent investigation will be more
important.

**Some general thoughts on mission technology planning**

The goals, objectives, and investigations all indicate that several
crucial technical capabilities require additional development. The most
important of these are: (1) *Global access*\--high and low latitudes,
rough and smooth surfaces, low and high elevations, in addition to
precision landing. (2) *Access to the subsurface*, from a meter to
hundreds of meters, directly (e.g., drilling) and indirectly (e.g.,
geophysical sounding). (3) *Access to time varying phenomena* that
requires the capability to make measurements over long periods (e.g.,
climate studies covering from one to several Martian years). (4) *Access
to microscopic scales* with instruments capable of measuring chemical
and isotopic compositions and determining mineralogy *as well the
ephemeral or continuous presence of liquid water on microscopic scales*.
(5) *Planetary protection and sample handling* that involve
implementation of cleaning methods, contamination control, sample
acquisition and processing methods, and sample packaging/sealing for
possible return to Earth. (6) *Advanced instrumentation*, especially *in
situ* life detection and age dating.

Orbital and landed packages could make many of the high priority
measurements, but others may require that samples be returned from Mars.
As noted in other MEPAG and National Academy of Science reports, study
of samples collected from known locations on Mars and from sites whose
geological context has been determined from remote sensing measurements
have the potential to significantly expand our understanding of Mars. A
full discussion of these issues is beyond the scope of this document,
and will be addressed by MEPAG science analysis groups in the near
future.

**Notes relating to this version of the Goals Document**

This present version of the Goals Document incorporates changes made by
the MEPAG Goals Committee and based on comments from the broader science
community. The Goals Committee provided comments and suggested revisions
using inputs from discussions held with the Mars community at the 7th
International Conference on Mars in July 2007. The Mars community was
then given the opportunity to comment on the draft revision from late
August to late September, 2007. The Goals Committee then prepared a
second revision that was circulated to the MEPAG Executive Committee in
December 2007. This revision was then discussed at the 18th MEPAG
meeting in February 2008, and the final version was posted in September,
2008 as part of the 19th MEPAG meeting.

Goal IV (Preparation for Human Exploration) was revised in 2005 with the
assistance of a MEPAG-chartered Mars Human Precursor Science Steering
Group (SSG) in order to update the 2001 and 2004 versions of the Goals
Document regarding the schedule and engineering implementation options
for human missions to Mars. With the exception of moving former Goal II,
Objective C ("Characterize the State and Processes of the Martian
Atmosphere of Critical Importance for the Safe Operation of
Spacecraft"), to Goal IV, Objective C, additional revision of Goal IV
has been deferred until additional studies currently underway by the
Mars Architecture Working Group are completed in 2008. Note also that
changes to Goal I recommended at the above meetings have not been
implemented owing to turnover in the Goal I representatives on the Goals
Committee in mid-2008. These changes will be implemented in the
subsequent revision to the Goals Document in 2009.

**I. GOAL: DETERMINE IF LIFE EVER AROSE ON MARS**

Determining if life ever arose on Mars is a challenging goal. The prime
focus of this goal is to determine if life is or was present on Mars. If
life exists or existed, another focus is to understand the systems that
support or supported it. Finally, if life never existed yet conditions
appear to have been suitable for formation and/or maintenance of life, a
focus would then be to understand why evidence of life was not found. A
comprehensive conclusion about the question of life on Mars will
necessitate understanding the planetary evolution of Mars and whether
Mars is or could have been habitable, and will need to be based in
multi-disciplinary scientific exploration at scales ranging from
planetary to microscopic. The strategy we have adopted to pursue this
goal has two sequential components: assess the habitability of Mars
(which needs to be undertaken environment by environment); and, test for
prebiotic processes, past life, or present life in environments that can
be shown to have high habitability potential. These constitute two
scientific objectives: "assess habitability" (A) and "test for life"
(C). A critical means to achieve both objectives is to characterize
Martian carbon chemistry and carbon cycling. Consequently, the science
associated with carbon chemistry is so fundamental to the overall life
goal that we have established it as a third primary science objective,
"follow the carbon" (B). To some degree, these scientific objectives can
be addressed simultaneously, as each requires basic knowledge of the
distributions of water and carbon on Mars and an understanding of the
processes that govern their interactions. Clearly, these objectives
overlap, but are considered separately.

In order to prioritize the objectives and investigations, we need to be
specific about the prioritization criteria. In broad perspective,
Objectives A ("assess habitability") and B ("follow the carbon") are the
critical steps in narrowing the search space to allow Objective C to be
addressed. Objective C ("test for life") is synonymous with Goal I and
is a long-term objective. We need to know where to look for life before
making a serious attempt at testing for life. At the same time,
Objectives A and B are fundamentally important even without searching
for life directly; they help us understand the role planetary evolution
plays in creating conditions in which life might have arisen, whether it
arose or not. Thus, objectives A, B, and C, in this order, form a
logical exploration sequence. Note that research goals and technology
development plans must incorporate both short- and long-term scientific
objectives. The rigorous development of instrumentation and flight
technologies is required to meet these objectives. Relevant tests would
identify, characterize, and curate laboratory samples from relevant
environments as part of ongoing efforts to improve detection limits.

**A. Objective: Assess the past and present habitability of Mars
(investigations listed in priority order)**

As used in this document, the term "habitability" refers to the
potential to support life of any form. Although Objective A is
considered at a planetary scale, we know from our experience on Earth
that we should expect that different micro-environments on Mars will
have different potential for habitability. It will not be possible to
make measurements of one environment and assume that they apply to
another. In order to address the overall goal of determining if life
ever arose on Mars, the most relevant life detection investigations
would be those carried out in environments that have high potential for
habitability. Thus, understanding habitability in space and time is an
important first order objective.

Arguably, until we discover an extant Martian life form and measure its
life processes, there is no way to know definitively which combination
of factors must simultaneously be present to constitute a Martian
habitat. Until then, "habitability" will need to describe the potential
of an environment to sustain life and will therefore be based on our
understandings of habitable niches on Earth or plausible extrapolations.
Current thinking is that at a minimum, the following four conditions
need to be satisfied in order for an environment to have high potential
for habitability:

-   The presence of liquid water. As we currently understand life, water
    is an essential requirement. Its identification and mapping
    (particularly in the subsurface, where most of Mars' water is
    thought to reside, but also as ephemeral water and hydrous mineral
    phases) must be accomplished on a global, regional and local basis
    using established measurement techniques.

-   The presence of the key elements that provide the raw materials to
    build cells.

-   A source of energy to support life.

-   The absence or protection from hazards detrimental to sustaining
    life (e.g., radiation).

Finally, environments with potential for habitability are assumed to
have unequal potential to preserve the evidence in geological samples.
There needs to be an understanding of these effects in order to
understand the significance of many types of life-related
investigations.

**[1. Investigation]{.underline}: Establish the current distribution of
water in all its forms on Mars.**

Water on Mars is thought to be present in a variety of forms and occur
in many locations, ranging from trace amounts of vapor in the atmosphere
to substantial reservoirs of liquid, ice and hydrous minerals that may
be present on or the below the surface. The presence of abundant water
is supported by its existence in the Martian perennial polar caps, the
geomorphic evidence suggestive of present-day ground ice and past
fluvial discharges, and by the Mars Odyssey GRS detection of abundant
hydrogen (which is interpreted to occur as water ice and/or hydrous
minerals) within the upper meter of the surface across much of the
planet. To investigate current habitability, the identity of the highest
priority H2O targets, and the depth and geographic distribution of their
most accessible occurrences, must be known with sufficient precision to
guide subsequent investigations. To understand the conditions that gave
rise to these potential habitats it is also desirable to characterize
their geologic and climatic context. The highest priority H~2~O targets
for the identification of potential habitats are: (1) liquid water \--
which may be present as pockets of brine in the near-subsurface, in
association with potential geothermally active regions (such as Tharsis
and Elysium), as super-cooled thin films within the lower cryosphere,
and beneath the cryosphere as confined, unconfined, or perched aquifers.
(2) Massive ground ice -- which may exist in a complex stratigraphy
beneath the northern plains and the floors of Hellas, Argyre, and Valles
Marineris (based on a the presumption of a Noachian ocean), the
geomorphic evidence for extensive and repeated flooding by Hesperian-age
outflow channel activity. These ground ice location may preserve
evidence of former life. and. (3) The polar layered deposits -- whose
strata may preserve evidence of climatically-responsive biological
activity (at the poles and elsewhere on the planet) and whose ice-rich
environment may allow for the episodic or persistent occurrences of
liquid water associated with climate change, local geothermal activity
and the presence of basal lakes.

**[2. Investigation]{.underline}: Determine the geological history of
water on Mars, and model the processes that have caused water to move
from one reservoir to another.**

In order to assess past habitability, we need to start with an
understanding, at global scale, of the abundance, form, and distribution
of water in Mars' geologic past. A first-order hypothesis to be tested
is whether Mars was at one time warmer and wetter than it is now. This
could be done, in part, through investigation of geological deposits
that have been affected by hydrological processes, and, in part, through
construction of carefully conceived models. One key step would be to
characterize the regional and global sedimentary stratigraphy of Mars.
It is entirely possible that Mars had life early in its history, but
that life is now extinct.

**[3. Investigation]{.underline}: Identify and characterize phases
containing C, H, O, N, P and S, including minerals, ices, and gases, and
the fluxes of these elements between phases.**

Assessing the availability and distribution of biologically important
elements and the phases in which they are contained, would allow a
greater assessment of both habitability and the potential for life to
have arisen. Detailed investigations for carbon are the primary focus of
Objective B and therefore will not be further discussed here. Nitrogen,
phosphorous and sulfur are critical elements for life on Earth and the
phases containing these elements and fluxes of these elements may
reflect biological processes and the availability of these elements for
life. They are often intimately associated with carbon and their
distribution is commonly controlled by water and oxidation states, so
interpreting these elemental cycles in terms of C, H, and O is extremely
valuable to understanding habitability. The redox chemistry of S is of
interest, because of its known role in some microbial metabolic
strategies in terrestrial organisms and the abundance of sulfate on the
surface of Mars.

**[4. Investigation]{.underline}: Determine the array of potential
energy sources available on Mars to sustain biological processes.**

This investigation would allow identification of the potential of Mars
to have harbored or continue to harbor life. Biological systems require
energy. Therefore, measurement of the availability of potential energy
sources is a critical component of habitability, and understanding how
life might use them is a critical component of designing scientifically
robust life detection experiments. Sources of energy that should be
measured may include chemical redox, pH gradients, geothermal heat,
radioactivity, incident radiation (sunlight), and atmospheric processes.

**B. Objective: Characterize Carbon Cycling in its Geochemical Context
(investigations listed in priority order)**

Carbon is the basic building block of life on Earth and it is assumed to
be the building block of life on Mars (if life exists/existed).
Understanding how carbon has been distributed on Mars through time,
including now, is critical for understanding where to look for life on
Mars, how life might have evolved on Mars, and how life might have
originated on Mars. In addition, there may be aspects of the carbon
cycle that reveal the existence of life (extant or extinct), and results
are likely to strongly influence approaches to searching for other
biosignatures. Thus, characterization of the carbon cycle is critical to
determining if life ever arose on Mars.

Understanding the origin of organic carbon is particularly important and
sources on Mars could be from several reservoirs that are summarized in
Table 2. Once organic carbon is discovered, a major challenge will be in
constraining the source and distribution of that organic carbon.
Terrestrial contamination is a significant concern, because of the need
to avoid false identification of organic carbon or specific organic
molecules on Mars. In addition, meteoritic delivery of organic carbon to
the surface of Mars and abiotic organic synthesis processes could
produce measurable organic carbon concentrations.

We assume that extraterrestrial life would be based on carbon chemistry
(Committee on the Limits of Organic Life in Planetary Systems, Committee
on the Origins and Evolution of Life, National Research Council, 116 p.,
2007). Although this assumption may subsequently need to be revised, we
would not know where else to begin in designing investigations of
possible extraterrestrial life. If anomalous measurements indicate the
presence of non-carbon based macromolecules associated with some form of
life-like processes then further experiments could be designed to
address this problem.

**Table 2**. Possible sources of organic carbon that need to be
distinguished in Martian samples.

  ----------------------- ---------------------------------------------------
  **Source of Carbon**    **Carbon compounds (examples/comments)**

  Prebiotic/protobiotic   Amino acids, purines and pyrimidines, polycyclic
  molecules from          aromatic hydrocarbons, chain hydrocarbons, fatty
  meteoritic / cometary   acids, carbohydrates, sugars and sugar derivatives.
  influx                  

  Prebiotic/protobiotic   Amino acids, purines and pyrimidines, polycyclic
  molecules from abiotic  aromatic hydrocarbons, chain hydrocarbons, fatty
  process on Mars         acids, carbohydrates, sugars and sugar derivatives.

  Terrestrial             Condensation products derived from rocket exhaust,
  contaminating organics  lubricants, plasticizers, atmospheric contaminants

  Terrestrial             Whole cells, cell components (LPS, DNA, proteins,
  contaminating organisms cytochromes)

  Terrestrial organisms   Organisms not present on the craft measuring them,
                          but had been previously transferred from Earth by
                          either meteorite impact or contamination of
                          previous spacecraft. Target molecules could include
                          individual genes, membrane constituents, specific
                          enzymes, and co-enzymes that would be expected to
                          be over expressed or adapted in Martian conditions.

  Terrestrial-like        Organisms that utilize terrestrial like
  organisms -- evolved on biochemistries and have evolved on Mars. Target
  Mars                    molecules could include individual genes, membrane
                          constituents, specific enzymes, and co-enzymes that
                          would be expected to be over expressed or adapted
                          in Martian conditions, or organisms using
                          metabolisms that would not be present on a space
                          craft contaminant such as methanogens,
                          psychrophiles endolithic survival mechanisms.

  Non-terrestrial-like    Utilizes an array of molecules for information
  organisms               storage, information transfer, compartmentalization
                          and enzymatic activity that differ from those used
                          by extant terrestrial life. Examples would be the
                          use of novel amino acids and nucleotides or the use
                          of novel nitrogen utilization strategies.

  Fossil biomarkers       Detection of established terrestrial fossil
                          biomarkers such as hopanes, archaeal lipids and
                          steranes, for the detection of the diagenetic
                          remains of terrestrial based life.
  ----------------------- ---------------------------------------------------

Note this table lists all possibilities without designating the
likelihood that a particular category exists.

**[1. Investigation:]{.underline} Determine the distribution and
composition of organic carbon on Mars.**

The spatial distribution and composition of organic carbon have not been
characterized, but are instrumental in understanding the biological
potential of Mars. (Methane and other simple reduced carbon molecules
are included as "organic carbon" in this context.) Abiotic synthesis of
organics, delivery of organics to Mars via meteorites, and possible
biological production of organics must all be evaluated in the context
of carbon cycling on Mars. Characterizing the molecular and isotopic
composition of organic carbon would be essential for determining the
origin of the organics shown in Table 2, which includes the types of
organic materials that need to be detected and deconvolved from each
other. Investigations require sufficient spacecraft cleaning and
verification to minimize the likelihood of contamination, in addition to
careful planning of specific methods to identify and exclude forward
contamination at the experiment level. Example measurements include
analysis of the concentration and isotopic composition of organic
carbon, characterization of the molecular structure of organic carbon,
or identifying and monitoring reduced carbon (e.g., methane) fluxes.

**[2. Investigation:]{.underline} Characterize the distribution and
composition of inorganic carbon reservoirs on Mars through time.**

Transformations of carbon between inorganic and organic carbon
reservoirs are a characteristic of life. Evaluating carbon reservoirs
and the fluxes between them would be critical to understanding both the
modern and geological evolution of carbon availability, and the
inorganic carbon reservoirs are an important link in the cycle. The
distribution of these reservoirs could also reveal critical habitability
information because they can record climate variations. Potential
measurements include continued searching for carbonate minerals from
orbit, in situ, and in returned samples, characterizing CO~2~ fluxes on
various time scales globally and locally, and measuring the isotopic
composition of any inorganic reservoir.

**[3. Investigation:]{.underline} Characterize links between C and H, O,
N, P, and S.**

The carbon cycle is intimately linked to H, O, N, P, and S, particularly
in the presence of life. Identifying connections among the geological
cycles of these elements will substantially aid interpretations of the
carbon cycle and may provide indicators that can be used to interpret
biological potential. Potential measurements include mineralogical
characterization of samples containing C, N, P, or S, isotopic and
oxidation state characterization of S-containing phases, and
identification of reactions involving any of these elements.

**[4. Investigation:]{.underline} Characterize the preservation of
reduced compounds on the near-surface through time.**

The surface of Mars is oxidizing, but the composition and properties of
the responsible oxidant(s) are unknown. Characterizing the reactivity of
the near-surface of Mars, including atmospheric (e.g., electrical
discharges) and radiation processes as well as chemical processes with
depth in the regolith[^3] and within weathered rocks is critical to
interpreting the paucity or possible absence of organic carbon on the
surface of Mars. Understanding the oxidation chemistry and the processes
controlling its variations will aid in predicting subsurface
habitability, considering that surface organic compounds likely have
been highly degraded by oxidation reactions and ionizing radiation from
space. Potential measurements include identifying the species and
concentrations of the oxidants, characterizing the processes forming and
destroying them, and characterizing concentrations and fluxes of redox
sensitive gases in the lower atmosphere.

**C. Objective: Assess whether life is or was present on Mars
(investigations listed in priority order)**

This objective reflects several of NASA's chief exploration goals. As
mentioned earlier, the need to prevent false positives or negatives, and
develop technology and experimental protocols, makes Objective C ("test
for life") a long-term goal. Objectives A ("assess habitability") and B
("follow the carbon") are the critical steps in narrowing the search
space to allow Objective C to be addressed. Furthermore, Objective C
itself does not halt upon a positive or negative answer. In the
eventuality of a positive answer, the next step would be to characterize
whatever life form is discovered, and then its origins and reason for
surviving on Mars. In the case of a negative answer, further
characterization of why life did not begin on Mars would become a
priority and in itself help us to understand more about life on Earth.

Determining whether life ever existed on Mars is a scientifically
exciting and challenging endeavor. The following investigations would
look for biosignatures, which are defined as results that REQUIRE the
presence or past presence of life. Commonly, multiple observations in a
context are required to identify biosignatures, and multiple scales of
observation are very important. Four investigations of features
currently recognized as biosignatures are listed here.

Investigation 1 (Characterize complex organics) is considered to be the
highest priority. Investigation 1 and some measurements to address
Investigation 4 would require sufficient spacecraft cleaning and
verification to avoid likelihood of contamination, in addition to
careful planning of specific methods to identify and exclude forward
contamination at the experiment level. Investigations 2 and 3, which
depend on the spatial distribution of signatures, are less sensitive to
contamination and might be more practical to pursue first. Remote
sensing techniques addressing investigation 4 also would have much lower
to no contamination issues. Investigations 1-4 are largely in situ
investigations that would be best conducted in those habitable
environments identified in A1.

A notional fifth investigation concept consists of suites of
observations based on correlations in biological indicators, which by
themselves are only suggestive for life and only in combination can
provide a true biosignature. It seems likely that many of the
combinations of measurements have yet to be identified, and it is
expected that innovative proposals for suites of observations will be
put forth to evaluate the past or present presence of life.

**[1. Investigation:]{.underline} Characterize complex organics.**

The identification of complex organics that can only be produced
biologically is a very strong biosignature, if forward contamination by
terrestrial organics can be excluded. Measurements for this
investigation must include appropriate methods to identify and exclude
forward contamination as a source of the target materials. To this end,
new techniques and instruments must be developed for cleaning and
monitoring of spacecraft contamination. Instruments must be developed to
include procedural blanks to allow accurate calibration measurements by
that instrument. This entails that the critical path of contamination,
i.e., the path the sample takes to the instrument, be cleaned to a level
below the detection limit of the instrument. Example measurements might
include characterization of organics such as DNA, nucleotides,
chlorophyll, etc. for extant life; hopanes, steranes, isoprenoids, etc.
for fossil life; or cumulative properties and/or distributions of
organics such as homochirality.

**[2. Investigation:]{.underline} Characterize the spatial distribution
of chemical and/or isotopic signatures.**

The spatial distribution of chemical or isotopic variations can be a
biosignature, if the distribution is inconsistent with abiotic
processes. Example measurements might include imaging of the
distribution of organics on a surface or in minerals; identifying
correlations among isotopic values and elemental concentrations that
reflect biological processes; or the presence of reduced and oxidized
gas phases in disequilibrium.

**[3. Investigation:]{.underline} Characterize the morphology or
morphological distribution of mineralogical signatures.**

Sedimentary and weathered rocks can preserve biosignatures in the
distribution of grains and minerals or in the morphology of biologically
produced minerals. Example measurements might include micron to
nanometer imaging and chemical analysis of crystals or morphological
characterization of sedimentary lamination to regional or global scale
characterization of sedimentary stratigraphy.

**[4. Investigation:]{.underline} Identify temporal chemical variations
requiring life.**

Extant life may be active, producing observable changes in chemistry
over the time scale in which a lander experiment may be functional.
Monitoring systems that may harbor life is an excellent way to identify
the presence of life. However, possible abiotic reactions need to be
thoroughly understood and forward contamination needs to be identified
or excluded. It is critical that measurements which are subject to
contamination include appropriate methods to identify and exclude
forward contamination as a source of the signatures being monitored.
Example measurements might include monitoring the flux of gases thought
to be biologically produced; monitoring oxidative changes in a way that
excludes abiotic reactions; or performing experiments to look for
metabolic processes.

**II. GOAL: UNDERSTANDING THE PROCESSES AND HISTORY OF CLIMATE ON MARS**

The fundamental scientific questions that underlie this goal are how the
climate of Mars has evolved over time to reach its current state, and
what processes have operated to produce this evolution. These scientific
questions are in accord with several key science objectives found in the
NASA Solar System Exploration Roadmap (2003). Mars climate can be
defined as the mean state and variability of its atmosphere and
exchangeable volatile reservoirs (near the surface) evaluated from
diurnal to geologic time scales. The climate history of Mars can be
divided into three distinct epochs: (i) Present, operating under the
current obliquity; (ii) Recent past, operating under similar pressures
and temperatures but over a range of orbital variations (primarily
obliquity); and (iii) Ancient, when the pressure and temperature may
have been substantially higher than at present and liquid water may have
been stable on the surface. An understanding of Mars climatic evolution
rests upon gaining a full understanding of the fundamental processes
governing its climate system, and thus upon obtaining detailed
observations of the current (observable) system. Goal II also is in line
with the recommendation of the Solar System Exploration Survey \[2002\],
which calls out the explicit need for Mars upper atmosphere measurements
to characterize current volatile escape rates for application to climate
evolution studies. Each Objective below corresponds to a different
climate epoch and are given in priority order. Objective A is focused on
the present state of the entire atmospheric system (from the
surface-atmosphere boundary to the exosphere). It would form the
baseline for interpreting past climates of Mars. Objective B is focused
on specific investigations that would provide information on the recent
period of climate history driven primarily by obliquity changes.
Objective C is focused on the ancient climate history, when Mars may
have been warmer, wetter and more habitable than today.

**A. Objective: Characterize Mars' Atmosphere, Present Climate, and
Climate Processes Under Current Orbital Configuration (investigations in
priority order)**

Our understanding of the composition and dynamics of the present Martian
atmosphere is the basis for understanding past climates on Mars.
Investigations of the upper and lower atmosphere plus the surface and
near-surface reservoirs of CO2, H2O and dust would be essential because
they are integral parts of an interconnected system. Measurements of
both atmospheric regions and the reservoir exchange region of the
regolith would enable us to explore different suites of processes that
play unique roles in understanding the Martian climate and its
evolution. In short, a ground-to-exosphere approach to monitoring the
Martian atmospheric structure and dynamics is needed for a proper
characterization of the present day climate of Mars.

**[1. Investigation:]{.underline} Determine the processes controlling
the present distributions of water, carbon dioxide, and dust by
determining the short- and long-term trends (daily, seasonal and solar
cycle) in the present climate. Determine the present state of the upper
atmosphere (neutral/plasma) structure and dynamics; quantify the
processes that link the Mars lower and upper atmospheres.**

To understand the present climate system, from the surface to the
exosphere, would require long-term (multi-year) continuous global
monitoring from both landed and orbital platforms. Understanding the
factors that control the annual variations of volatiles and dust is
necessary to determine to what extent processes operating today have
controlled climate change in the past.

*(i) Lower atmosphere climate and processes*

In situ measurements are uniquely suited to measure locally near-surface
water vapor, winds, heat, momentum, and mass fluxes, and other variables
that control the exchange of volatiles and dust between the surface and
atmosphere. In situ measurements could be obtained by stationary landed
observatories (individual or networked), mobile platforms (e.g.,
rovers), and aerial platforms (e.g., balloons). Each of these platforms
could provide unique measurements critical to a complete understanding
of the climate system. In situ measurements could also provide
calibration and validation for complementary measurements retrieved from
orbit.

Orbital missions could provide information on the global and vertical
structure of the atmosphere, direct measurement of winds, and
information on the spatial distribution of aerosols, water vapor, clouds
(both water and CO~2~) and potentially other important trace species.
This information leads to the elucidation of the local- through
global-scale processes that operate to maintain the climate and
transport volatiles and dust. The global meteorological, radiative, and
mass balance observations gathered from these platforms on daily- to
decade-long timescales would establish the magnitude of inter-annual
variability, aid in the identification of the responsible mechanisms,
and demonstrate whether there are any long-term trends in the present
climate system. Specifically, these measurements would provide a means
to characterize the annual variations and cycling of volatiles,
condensates, and dust. These observations would also assist in
identifying the causes of the north/south asymmetry in the nature of the
polar caps, and the physical characteristics of the layered deposits.
Ultimately, these data would serve as the foundation for the development
of more realistic models to assess the effects of various external
forcing-factors (such as obliquity and increased atmospheric pressure)
on the climate of Mars.

*(ii) Upper atmosphere climate and processes*

Orbiter missions would also be needed to investigate the mean state and
variability of the neutral and plasma environment above \~80 km. These
data would improve our understanding of the coupling of the lower and
upper atmospheres, and characterize the regions of the upper atmosphere
that interact with the solar wind. Also, the global characterization of
the present lower and upper atmosphere structure and dynamics would be
required over various timescales (daily, seasonal, and solar cycle) in
order to properly interpret volatile escape measurements and the
subsequent volatile evolution model results. This objective reemphasizes
the need for a ground-to-exosphere approach to monitoring of the Martian
atmospheric structure and dynamics.

*(iii) Planetary boundary layer: heat, momentum and mass exchange*

Thermal variation between the surface and the atmosphere combined with
mechanical interactions between the wind and surface roughness element
drives turbulence. The links between surface and air temperature (via
aerosol radiative heating) and the thermodynamic state of the lower
atmosphere will be studied under this investigation. Turbulence and heat
transport in the lowest portion (\<5km) of the atmosphere would also be
a concern for thermal design of spacecraft.

**[2. Investigation:]{.underline} Determine the production/loss,
reaction rates, and global 3-dimensional distributions of key
photochemical species (e.g., O~3~, H~2~O, CO, OH, CH~4~, SO~2~), the
electric field and key electrochemical species (e.g., H^2^O~2~), and the
interaction of these chemical species with surface materials.**

This investigation would necessarily involve study of both the lower and
upper atmosphere. Surface sinks and sources and lower atmospheric
distribution would be required to interpret atmospheric escape rates and
upper atmosphere aeronomic processes. Current multi-dimensional
photochemical models predict global distributions of these species. Such
models require validation to confirm key reactions and rates and the
role of dynamics in the transport of these constituents. There is,
however, considerable uncertainty in the surface fluxes of major
species. In particular, the absolute abundance and the corresponding
spatial/temporal variability of CH~4~ are uncertain, but have important
implications for Mars biological or non-biological processes (see
section I.B). In addition, electro-chemical effects may be important for
production of certain species (e.g. H~2~O~2~) and promoting
surface-atmosphere reactions, but confirmation is needed. This
investigation would require global orbiter observations of neutral and
ion species, temperatures, and winds in the lower and upper atmospheres,
and the systematic monitoring of these atmospheric fields over multiple
Mars years to capture inter-annual variability induced by the solar
cycle, seasons, and dust storms.

**[3. Investigation:]{.underline} Understand how volatiles and dust
exchange between surface and atmospheric reservoirs, including the mass
and energy balance. Determine how this exchange has affected the present
distribution of surface and subsurface ice as well as the Polar Layered
Deposits (PLD).**

The current Martian seasonal cycle is dominated by condensation and
evaporation of 1/3 of the carbon dioxide atmosphere into the seasonal
caps. Both dust and water ice are entrained in this seasonal wave and
may be incorporated into more permanent icy deposits. Mechanisms of
deposition ("snow", direct condensation) as well as evolution and
densification of deposits bear directly on the stability, evaporation
and venting of those deposits in spring. The onset of sporadic,
planet-encircling dust events coincides with the retreat of the south
seasonal cap, but their timing and causes are still not well understood.
Exposure of permanent water ice deposits in the north drives the water
cycle and exchange with the atmosphere. Transport of dust and water in
and out of the polar regions are seasonally, annually, and decadally
variable, requiring long-term monitoring. Large scale sub-surface ice
deposits exist at high latitudes in both hemispheres and may buffer
long-term surface-atmosphere exchange. This investigation would require
measurement of both mass and energy balances of volatiles and dust
within the permanent and seasonal volatile reservoirs: polar layered
deposits, buried ice rich soils, seasonal ice deposits and the
atmosphere. Assessment of net accumulation or loss of the residual ice
deposits and mass, density and volume of the seasonal ice as function of
location and time are important components of this investigation.

**[4. Investigation:]{.underline} Search for microclimates.**

Detection of exceptionally or recently wet or warm locales,
exceptionally cold localities, and areas of significant change in
surface accumulations of volatiles or dust would identify sites for in
situ exploration. This would require a global search for sites based on
local surface properties (e.g., geomorphic evidence, topography, thermal
properties, albedo) or changes in volatile (especially H~2~O)
distributions.

**B. Objective: Characterize Mars' Recent Climate History and Climate
Processes Under Different Orbital Configurations (investigations in
priority order)**

Understanding the climate and climate processes of Mars under past, but
geologically recent, orbital configurations would require
interdisciplinary study of the Martian surface and atmosphere. The
investigations described below focus on quantitative measurements
(concentrations and isotopic compositions) of important gases in the
atmosphere and trapped in surface materials. It also would require the
study of geologic materials to search for the record of past climates.
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 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 may reflect recent high obliquity cycles within the
last few million years.

**[1. Investigation:]{.underline} Determine how the stable isotopic,
noble gas, and trace gas composition of the Martian atmosphere has
evolved over obliquity cycles to its present state.**

This investigation would require knowledge of the composition of the
atmosphere at various times within recent climate history to provide
quantitative constraints on the evolution of atmospheric composition and
on the sources and sinks of the major gas inventories. It is important
to understand the temporal and spatial variability of atmospheric
composition. In situ or returned sample high precision isotopic
measurements of the present atmosphere, and analogous measurements of
trapped guesses within polar layered deposits or other gas-preserving
ices, would be required.

**[2. Investigation:]{.underline} Determine the chronology, including
absolute ages, of compositional variability, and determine the record of
recent climatic change that are expressed in the stratigraphy of the
PLD.**

The presence of extensive layered deposits suggests that the climate of
Mars has undergone frequent and geologically recent change. A key to
understanding the climatic and geologic record preserved in these
deposits is to determine the environmental conditions and processes that
were necessary to produce them. Specific examples of the type of
information these deposits may preserve include a stratigraphic record
of volatile mass balance; insolation variations; atmospheric
composition; dust storm, volcanic and impact activity; cosmic dust;
catastrophic floods; solar luminosity (extracted by comparisons with
terrestrial ice cores); supernovae and perhaps even a record of
microbial life. Clues to climate evolution are recorded in the
stratigraphy and physical and chemical properties of the layers. Keys to
understanding the climatic and geologic record preserved in these
deposits are to determine the relative and absolute ages of the layers,
their thickness, extent and continuity, and their petrologic/geochemical
characteristics (including both isotopic and chemical composition).
Addressing this investigation would require high-resolution imaging, in
situ and remote sensing measurements of stratigraphy and layer
properties, and absolute ages determined either in situ or from returned
samples.

**[3. Investigation:]{.underline} Relate low latitude terrain softening
and periglacial features to past climate eras.**

Recent high resolution imaging has shown numerous examples of flow-like
features on the slopes of Tharsis volcanoes and in other lower-latitude
regions. These features, interpreted to be glacial and peri-glacial, may
be related to ground ice accumulation in past obliquity extremes. This
investigation would link observed deposits to past orbital conditions
primarily through models and age dating and additional investigations in
Goal III.A.

**C. Objective: Characterize Mars' Ancient Climate and Climate Processes
(investigations in priority order)**

Understanding the ancient climate and climate processes on Mars requires
interdisciplinary study of the Martian surface and atmosphere. There is
great uncertainty about the composition and state (pressure and
temperature) of the ancient atmosphere and its ability to support liquid
water on the surface. The investigations described below would focus on
the study of atmospheric escape processes and the study of geologic
features and geochemical signatures. Understanding atmospheric loss
processes enable extrapolation backwards in time to better estimate the
atmospheric conditions present during the ancient climate regime and
better understand the evolution of the ancient climate to its present
day condition. Observations of present geomorphology and geochemistry
record the integrated climate history of Mars from ancient times to
present. The atmospheric and geologic record must be used
synergistically to decode a self-consistent picture of the ancient
climate and climate evolution of Mars.

**[1. Investigation:]{.underline} Determine the rates of escape of key
species from the Martian atmosphere, their correlation with seasonal and
solar variability, the influence of remnant crustal magnetic fields, and
their connection with lower atmosphere phenomenon (e.g., dust storms).
From these observations, quantify the relative importance of processes
that control the solar wind interaction with the Mars upper atmosphere
in order to establish the magnitude of associated volatile escape
rates.**

These measurements would provide crucial constraints to atmospheric
evolution models that extrapolate these rates to determine past
climates. This investigation would require global orbiter observations
of neutral and plasma species, crustal magnetic fields, temperatures,
and winds in the extended upper atmosphere. The systematic monitoring of
these fields over multiple Mars years is needed to capture the
inter-annual variability induced by the solar cycle, seasons, and dust
storms. This investigation also would require more thorough and
higher-resolution measurements of crustal magnetic fields.

**[2. Investigation:]{.underline} Find physical and chemical records of
past climates.**

This investigation would center on finding geomorphic and chemical
evidence of past climates or of prior environmental events or conditions
that may have perturbed the local or global climate in unexpected ways
(e.g., the former presence of an ocean or seas or of global magnetic
fields, large impacts, episodic volcanism or outflow channel activity).
These would provide the basis for understanding the extent, duration
(e.g., gradual change or abrupt transition), and timing of past climates
on Mars. This investigation would require, for example, determining
sedimentary stratigraphy and the distribution of aqueous weathering
products. Specific investigations are further elaborated in Goal III.A.

**[3. Investigation:]{.underline} Determine how the stable isotopic,
noble gas, and trace gas composition of the Martian atmosphere has
evolved through time from the ancient climate state.**

These provide quantitative constraints on the initial atmospheric
inventory of gases that are needed to determine the evolution of
atmospheric composition to its present state. It would require
high-precision dating and isotopic measurements of Martian meteorites
and returned samples.

**III. GOAL: DETERMINE THE EVOLUTION OF THE SURFACE AND INTERIOR OF
MARS**

Insight into the composition, structure, and history of Mars is
fundamental to understanding the solar system as a whole, as well as
providing insight into the history and processes of our own planet.
There are compelling scientific motivations for the study of the surface
and interior of the planet in its own right. The geology of Mars sheds
light on virtually every aspect of the study of conditions potentially
conducive to the origin and persistence of life on that planet, and the
study of the interior provides important clues about a wide range of
topics, such as geothermal energy, the early environment, and sources of
volatiles.

A critical aspect of Mars is the evidence for the presence and activity
of liquid water on or near the surface over an extended period of time.
This has enormous geological implications affecting, for example,
erosion, weathering, heat flow, and the possibility of life (which can,
in turn, have significant effects on geological processes).

**A. Objective: Determine the nature and evolution of the geologic
processes that have created and modified the Martian crust
(investigations in priority order)**

The Martian crust contains the record of all the processes that shaped
it, from initial differentiation and volcanism, to modification by
impact, wind, and water. Understanding that record would help us
understand the early environment (as reflected, for example, in the
alteration mineralogy), the total inventory and role of water, regions
likely to have been habitable, processes involved in surface-atmosphere
interactions, and the planet's thermal history. Many of the listed
investigations are interrelated and could be addressed by common data
sets and/or methodologies. In many cases, the reasons for separating
some subjects into different investigations have to do with issues of
scale (both vertical and lateral) or geologic/geophysical process. For
the purposes of Goal III, "regolith" refers to the upper few meters to
hundreds of meters of the Martian surface; greater depths are treated as
part of the crust.

**[1. Investigation:]{.underline} Determine the formation and
modification processes of the major geologic units and surface regolith
as reflected in their primary and alteration mineralogies.**

The regolith is a filter through which we view most of the Martian
surface by remote sensing. In addition, it may provide a valuable record
of the history of surface conditions and processes. Understanding Mars'
geologic/environmental history, including regolith formation and
modification, requires quantitative measurement of mineralogy and
chemistry. Identification of alteration processes requires
characterization of both unaltered and altered rock. There have been
considerable advances in the understanding of surface mineralogy based
on remote sensing and limited in situ observations. Orbital remote
sensing with high spatial and spectral resolution has demonstrated the
ability to correlate mineralogy with specific geologic units. However,
calibration of the orbital data with in situ direct determination of
mineralogy is critical, both to ensure the interpretations based on
orbital data are correct and to understand those species that either
have limited spatial extent or concentration or which can not be
detected in remote observation.

**[2. Investigation:]{.underline} Evaluate volcanic,
fluvial/laucustrine, hydrothermal, and polar erosion and sedimentation
processes that modified the Martian landscape over time.**

Sediments and sedimentary rocks formed in and near fluvial, laucustrine,
or other deposition regimes are the most likely materials to preserve
traces of prebiotic compounds and evidence of life. Sediments and
sedimentary rocks record the history of aqeuous processes. Aeolian
sediments record a combination of globally averaged and locally derived
fine-grained sediments and weathering products. Pyroclastic deposits
record a style of volcanism that commonly involves interactions with or
compositions containing relatively abundant volatiles. Understanding
this wide variety of sedimentary processes requires knowledge of the
ages, sequences, and mineralogies of sedimentary rocks; as well as the
rates, durations, environmental conditions, and mechanics of weathering,
cementation, and transport.

**[3. Investigation:]{.underline} Constrain the absolute ages of major
Martian crustal geologic processes, including sedimentation, diagenesis,
volcanism/plutonism, regolith formation, hydrothermal alteration,
weathering, and the cratering rate.**

The evolution of the interior and surface, as well as the possible
evolution of life, must be placed in an absolute timescale, which is
presently lacking for Mars. Without an understanding of the absolute
timing of events, the potential for current geologic/biologic activity
remains unknown. Developing this chronology requires determining the
absolute ages of crystallization or impact metamorphism of individual
units with known crater frequencies. This would allow calibration of
Martian cratering rates and interpretations of absolute ages of geologic
units. This investigation could be approached with both in situ and
returned sample analysis, although with different precision.

**[4. Investigation:]{.underline} Hydrothermal environments.**

Hydrothermal environments provide a potentially unique environmental
niche in which life may presently exist, or in which life may have
existed in the past. It is also an important indicator of past volcanic
and thermal activity. Should life (extant or extinct) be found in such
an environment, it would serve as a possible basis for understanding the
earliest evolution of life on the Earth. Hydrothermal systems may also
play an important role in the chemical and isotopic evolution of the
atmosphere and the formation of the regolith, and may record the
histories of these events. The search for active hydrothermal systems
would require high spatial resolution thermal data; the search for
active or past hydrothermal systems might be conducted by searching for
high-temperature alteration minerals or those associated with those
environments, such as amorphous silica.

**[5. Investigation:]{.underline} Evaluate igneous processes and their
evolution through time.**

This investigation includes the broad range of igneous processes such as
the mineralogy and petrology of the rocks as well as, for example,
volcanic outgassing and volatile evolution. In addition to dramatically
shaping the surface of the planet, volcanic processes are the primary
mechanism for release of water and atmospheric gasses. Sites of present
day volcanism, if any, might be prime sites to investigate.
Understanding primary lithologies also is a key to interpreting
alteration processes that have produced secondary mineralogies.

**[6. Investigation:]{.underline} Characterize surface-atmosphere
interactions on Mars, as recorded by aeolian, glacial/periglacial,
fluvial, chemical and mechanical erosion, cratering and other
processes.**

The focus of this investigation would be on the processes that have
operated within the recent past. Studying surficial features resulting
from recent hydrologic, glacial/periglacial, cratering, and atmospheric
processes, as well as those associated with chemical and physical
erosion, contributes to our understanding of which features may (or may
not) indicate possible locations for near-surface water and helps us
interpret features formed in past environments. Integrating information
about the morphology, chemistry and mineralogy of surface deposits is
essential for understanding alteration processes. It would require
orbital and surface-based remote sensing of the surface (microns to
centimeters) and direct measurements of sediments and atmospheric
boundary layer processes.

**[7. Investigation:]{.underline} Determine the tectonic history and
large-scale vertical and horizontal structure of the crust, including
present activity. This includes, for example, the structure and origin
of hemispheric dichotomy.**

Understanding the tectonic record and the structures within the crust
over large vertical and horizontal scales is crucial for understanding
the geologic history as well as the temporal evolution of internal
processes. This, in turn, places constraints on release of volatiles
from differentiation and volcanic activity and the effect of tectonic
structures (faults and fractures in particular) on subsurface hydrology.
Determining these structures would require gravity data, deep subsurface
sounding (100's of meters to kilometers), detailed geologic and
topographic mapping (including impact mapping/studies), and
determination of the compositions of major geologic units. A long-term,
continuously active seismic network composed of multiple stations would
be required to understand the distribution and intensity of current
tectonic activity.

**[8. Investigation:]{.underline} Determine the present state,
3-dimensional distribution, and cycling of water on Mars including the
cryosphere and possible deep aquifers.**

Water is an important geologic agent on Mars, influencing most
geological processes including the formation of sedimentary, igneous and
metamorphic rocks, the weathering of geological materials, and
deformation of the lithosphere. Determining the distribution of water in
its various phases and in different locations would require global
observations using various types of subsurface sounding techniques and
remote sensing, coupled with detailed local and regional sounding and
measurements.

**[9. Investigation]{.underline}: Determine the nature of crustal
magnetization and its origin.**

The magnetization of the Martian crust is only poorly understood from
Mars Global Surveyor magnetometer data, but is intimately related to the
geothermal history of the planet. Addressing this problem would require
high-resolution (spatial and field strength) mapping of the magnetic
field and determining of the crustal mineralogy (particularly the
magnetic carries), geothermal gradient, and magnetization of geologic
units.

**[10. Investigation:]{.underline} Evaluate the effect of large-scale
impacts on the evolution of the Martian crust.**

Impacts are one of the most important of the processes shaping the crust
and surface of Mars. A detailed understanding of effects of impact
events (e.g., those producing quasi-circular depressions and basins) on
the structural, topographic and thermal history of Mars is a
prerequisite for any broad understanding of the history of the crust and
lithosphere. Understanding impact effects would require geologic mapping
using global topographic data combined with high-resolution images and
remote sensing data.

**B. Objective: Characterize the structure, composition, dynamics, and
evolution of Mars' interior (investigations in priority order).**

Investigating the internal dynamics and structure of Mars would
contribute to understanding the bulk chemical composition of the planet,
the evolution of its crust, mantle, and core, its thermal evolution, the
origin of its magnetic field, and the nature and origin of the geologic
units. These are fundamental aspects of Mars that form the basis of
comparative planetology.

**[1. Investigation:]{.underline} Characterize the structure and
dynamics of the interior.**

Understanding the structure and dynamical processes of the mantle and
core is fundamental for understanding the origin and evolution of Mars,
its surface evolution, and the release of water and atmospheric gasses.
For example, the thickness of the crust and the size of the core provide
strong constraints on the bulk composition of the planet, its thermal
history, and the manner in which it differentiated. This investigation
would require seismology (e.g., passive and active experiments and
understanding of the seismic state of the planet), heat flow, and
gravity data.

**[2. Investigation:]{.underline} Determine the origin and history of
the magnetic field.**

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 an early atmosphere and for the shielding of the
surface from incoming radiation. The collection of high-precision,
high-resolution global, regional, and local magnetic measurements,
calibration of the ages of surfaces, and measurements of the magnetic
properties of samples would now be required.

**[3. Investigation]{.underline}: Determine the chemical and thermal
evolution of the planet.**

Knowledge of the chemical and thermal evolution places constraints on
the composition, quantity, and rate of release of volatiles (water and
atmospheric gasses) to the surface. This investigation would require
measurements of the internal structure, thermal state, surface
composition and mineralogy, and geologic relationships. These data could
be obtained through analysis of the seismic velocity profile, heat flow
measurements, and study of the mineralogy and geochemistry of xenoliths
in volcanic and plutonic rocks.

**C. Objective: Understand the origin, evolution, composition and
structure of Phobos and Deimos (investigations in priority order).**

**[1. Investigation:]{.underline} Determine the origin of Phobos and
Deimos.**

These two satellites may represent captured asteroids, pieces of the
Martian crust ejected during large basin formation, or residual
accretionary debris. Understanding their origin would allow an
understanding of the extent to which they represent pieces of Mars.

**[2. Investigation:]{.underline} Determine the composition of Phobos
and Deimos.**

Understanding the chemical and mineralogic composition of thee
satellites would provide insight into their origin. Analysis of surface
materials might also indicate whether the satellites preserve materials
ejected from the surface of Mars. Such analyses would also shed light on
processes of space weathering in the Martian environment. Understanding
the pristine chemistry and mineralogy would require analysis of material
unaffected by space weathering; this, in turn, would require the
collection and analysis of subsurface materials.

**[3. Investigation:]{.underline} Understand the internal structure of
Phobos and Deimos.**

Determining the internal structure of these bodies would provide
information on their origin, formation and evolution. They might be
rubble piles or rocks bodies with a surface regolith. Determining their
internal structure would require an active seismic experiment as they
are unlikely to exhibit endogenic seismic activity.

IV\. GOAL: PREPARE FOR HUMAN EXPLORATION

Robotic missions serve as logical precursors to eventual human
exploration of space. In the same way that the Lunar Orbiters, Ranger
and Surveyor landers paved the way for the Apollo Moon landings, a
series of robotic Mars Exploration Program missions is charting the
course for future human and robotic exploration of Mars. Goal IV of the
MEPAG document differs from the previous Goals in that it addresses
science and engineering questions specific to increasing the safety,
decreasing the cost, and increasing the productivity of human crews on
Mars. To address these issues this section describes both the data sets
that are to be collected and analyzed (Objective A), and the
demonstrations of critical technologies that must be validated in the
Martian environment (Objective B). Finally, Objective C highlights
mission critical atmospheric measurements that would reduce mission risk
and enhance overall science return, benefiting all future missions to
the planet (both robotic and human). No attempt has been made to
prioritize these risk mitigation and engineering related measurements
since all are important.

The 2004 National Vision for Space Exploration provides guidance for a
broad range of human and robotic missions to the moon, Mars and
destinations beyond. Robotic missions serve as one component of a
"system of systems", the sum of which work together to accomplish the
goals of implementing a safe, sustained, and affordable robotic and
human program to explore and extend human presence across the solar
system and beyond. One of the Vision's main points is to conduct robotic
exploration of Mars to prepare for human exploration, and NASA has
adopted a "level zero" requirement to "conduct robotic exploration of
Mars to search for evidence of life, to understand the history of the
solar system, and to support future human exploration activities."
Specifically, robotic precursor missions would be used in part to
acquire and analyze data for the purpose of reducing cost and risk of
future human exploration missions, would perform technology and flight
system demonstrations for the purpose of reducing cost and risk of
future human exploration missions, and would deploy infrastructure to
support future human exploration activities.

As part of the momentum associated with the 2004 National Vision for
Space Exploration, in 2004-2005 MEPAG undertook a major reassessment of
the issues associated with preparing for the human exploration of Mars.
This work is summarized in the following two documents, which represent
analyses of Goal IV Objective A, and Goal IV Objective B, respectively.
The logic associated with the investigations and measurements is
described in these reports.

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.

Hinners, N.W., Braun, R.D., Joosten, K.B., Kohlhase, C.E., and Powell,
R.W., (2005), Report of the MEPAG Mars Human Precursor Science Steering
Group Technology Demonstration and Infrastructure Emplacement (TI)
Sub-Group, 24 p. document posted July, 2005 by the Mars Exploration
Program Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>.

**A. Objective. Obtain knowledge of Mars sufficient to design and
implement a human mission with acceptable cost, risk and
performance.**[^4]

*[Investigations #1A-1D are judged to be of indistinguishable high
priority.]{.underline}*

**[1A. Investigation.]{.underline} Characterize the particulates that
could be transported to hardware and infrastructure through the air
(including both natural aeolian dust and other materials that could be
raised from the Martian regolith by ground operations), and that could
affect engineering performance and *in situ* lifetime. Analytic fidelity
sufficient to establish credible engineering simulation labs and/or
performance prediction/design codes on Earth is required.**

[Measurements]{.underline}

a\. A complete analysis, consisting of shape and size distribution,
mineralogy, electrical and thermal conductivity, triboelectric and
photoemission properties, and chemistry (especially chemistry of
relevance to predicting corrosion effects), of samples of regolith from
a depth as large as might be affected by human surface operations.

> *Note #1: For sites where air-borne dust naturally settles, a bulk
> regolith sample would be sufficient---analysis of a separate sample of
> dust filtered from the atmosphere is desirable, but not required.*
>
> *Note #2: Obtaining a broad range of measurements on the same sample
> would be considerably more valuable than a few measurements on each of
> several samples (this naturally lends itself to sample return).*
>
> *Note #3: There is not consensus on adding magnetic properties to the
> list of measurements.*

b\. Characterize at least one regolith deposit with fidelity sufficient
to establish credible engineering simulation labs and/or software codes
on Earth to solve engineering problems related to differential
settlement of the regolith, and plume/regolith interactions (see Note
#4).

> For one site on Mars (see Note #5), measure the following properties
> of the regolith as a function of depth to 1 meter:
>
> Particle shape and size distribution
>
> Ice content and composition to within 5% by mass
>
> Regolith density to within 0.1 g/cm^3^
>
> Gas permeability in the range 1 to 300 Darcy with a factor of three
> accuracy
>
> Presence of significant heterogeneities or subsurface features of
> layering
>
> An index of shear strength
>
> Flow Rate Index test or other standard flow index measurement
>
> Repeat the above measurements at a second site in different geologic
> terrane.

c\. The same measurements as above on a sample of air-borne dust
collected during a major dust storm.

d\. Subsets of the complete analysis described above, and measured at
different locations on Mars (see Note #2). For individual measurements,
priorities are:

> shape and size distribution and mineralogy\
> electrical\
> chemistry

*[Note #4]{.underline}. Because there is a large engineering lead-time
required to solve the geotechnical problems, these data must be obtained
early in the precursor program.*

*[Note #5]{.underline}. These measurements should be made in a competent
regolith deposit as opposed to loose drift material (cohesionless sand
dunes), as landing is expected to attempt to avoid the looser material.
Also, if mission planners would select high latitude polar deposits for
a human landing site, geotechnical data would be required from a
representative location of those deposits. These measurements should
include polarity and magnitude of charge on individual dust particles
suspended in the atmosphere and concentration of free atmospheric ions
with positive and negative polarities. Measurement should be taken
during the day in calm conditions representative of nominal Extra
Vehicular Activity (EVA) excursions.*

**[1B. Investigation.]{.underline} Determine the atmospheric fluid
variations from ground to \>90 km that affect EDL and TAO including both
ambient conditions and dust storms.**

[Measurements:]{.underline}

a.  Measure velocity (v), pressure (P), temperature (T) and density (ρ)
    in the upper, middle and lower atmosphere during EDL. Obtain as many
    profiles at various times and locations as possible (requested for
    all landed missions). Sample rate should be high enough (\~100 Hz)
    to quantify turbulent layers. Specific direct or derived
    measurements would include:

-   Density from 120 km to surface ranging from high altitude values of
    10^-9^ to near-surface values of 10^-1^ kg/m^3^, dρ = 1% of local
    ambient

-   Pressure from 120 km to surface ranging from high altitude values of
    10^-7^ to near-surface values of 15 mb, dP= 1% of local ambient

-   Temperature 60-300 K, dT = 0.5K

-   Directional Wind Velocity, 1-50 m/sec, dv = 1 m/s

> Particular emphasis on measurements between 0-20 km to quantify
> boundary layer wind and turbulence and 30-60 km where vehicle dynamic
> pressure is largest.

a.  Monitor surface/near-surface velocity (v(z)), pressure (P),
    temperature (T(z)), and density (ρ) as a function of time. Quantify
    the nature of the surface heating driver and associated boundary
    layer turbulence at altitudes above station. Data defines the
    initial conditions for high altitude modeling. Obtain data from as
    many locations as possible (requested for all landed missions).
    Surface/near surface packages should measure directly:

-   Pressure, at surface, 0.005 mb to 15 mb, dP = 2 microbar, full
    diurnal sampling, rate= \>10 Hz

-   Velocity, at surface, 0.05-50 m/sec, dv = 0.05 m/s, horizontal and
    vertical, full diurnal sampling, rate= 10 Hz

-   Air temperature, at surface, 150-300 K, dt = 0.04K, full diurnal
    sampling, rate= 10 Hz

-   Ground temperature 150-300 K, dt = 1K, full diurnal sampling, rate=
    1 Hz

-   Air temperature profile, 0-5km, \<1km resolution, 150-300K, dt=2K,
    full diurnal sampling, rate=1 Hz

-   Velocity profile, 0-5km, \<1km resolution, 1-50 m/sec, dv=1 ms/,
    horizontal and vertical, full diurnal sampling, rate=1 Hz

-   Opacity, visible, depth 0.2-10, dtau = 0.1, once every 10 min

c.  Make long-term (\>\> 1 Martian year) remote sensing observations of
    the weather (atmospheric state and variations) from orbit, including
    a direct or derived measurement of:

-   Aeolian, cloud, and fog event frequency, size, distribution as a
    function of time.

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-   Vertical temperature profiles from 0-120 km with better than 1 km
    resolution between 0-20 km, 1-3 km resolution between 20-60 km, 3 km
    resolution \> 60 km and with global coverage over the course of a
    sol, all local times *\[Development work required for T from surface
    to 20 km\].*

-   Vertical density/pressure profiles from 0-120 km with better than 1
    km resolution between 0-20 km, 1-3 km resolution between 20-60 km, 3
    km resolution \> 60 km and with global coverage over the course of a
    sol, all local times *\[Development work required for ρ from surface
    to 20 km\].*

> 3-D winds as a function of altitude, from 0-60 km with better than 1
> km resolution below 20 km, and 1-3 km resolution between 20-60 km, and
> with global coverage over the course of a sol, all local times
> *\[Development work required at all altitudes for an independent means
> to derive V, with special emphasis from surface to 20 km\].*
>
> Note particular emphasis on measurements between 0-20 km to quantify
> boundary layer wind and turbulence and 30-60 km where vehicle dynamic
> pressure is large.

d.  At time of human EDL and TAO, deploy ascent/descent probes into
    atmosphere to measure pressure, temperature and velocity just prior
    to human descent at scales listed in 1Ba.

*[Note #6]{.underline}: We have not reached agreement on the minimum
number of atmospheric measurements described above, but it would be
prudent to instrument all Mars atmospheric flight missions to extract
required vehicle design and environment information. Our current
understanding of the atmosphere comes primarily from orbital
measurements, a small number of surface meteorology stations and a few
entry profiles. Each landed mission to Mars has the potential to gather
data that would significantly improve our models of the Martian
atmosphere and its variability. It is thus desired that each opportunity
be used to its fullest potential to gather atmospheric data.
Reconstructing atmospheric dynamics from tracking data is useful but
insufficient. Properly instrumenting entry vehicles would be required.*

**1C. Investigation. Determine if each Martian site to be visited by
humans is free, to within acceptable risk standards, of biohazards that
may have adverse effects on humans and other terrestrial species.
Sampling into the subsurface for this investigation must extend to the
maximum depth to which the human mission might come into contact with
uncontained Martian material.**

[Measurements:]{.underline}

a.  Determine if extant life is widely present in the Martian
    near-surface regolith, and if the air-borne dust is a mechanism for
    its transport. If life is present, assess whether it is a biohazard.
    For both assessments, the required measurements are the tests
    described in the Draft Test Protocol.

*[Note #7]{.underline}: To achieve the necessary confidence, this would
require sample return and analyses in terrestrial laboratories.*

*[Note #8]{.underline}: The samples could be collected from any site on
Mars that is subjected to wind-blown dust.*

*[Note #9]{.underline}: At any site where dust from the atmosphere is
deposited on the surface, a regolith sample collected from the upper
surface would be sufficient\--it is not necessary to filter dust from
the atmosphere.*

b.  At the site of the planned first human landing, conduct biologic
    assays using *in situ* methods, with measurements and instruments
    designed using the results of all prior investigations. All of the
    geological materials with which the humans and/or the flight
    elements that would be returning to Earth come into contact need to
    be sampled and analyzed.

*[Note #10]{.underline}: It is recommended that a decision on whether
human landing sites after the first one would require a lander with
biological screening abilities be deferred until after Measurement a has
been completed.*

**[1D. Investigation.]{.underline} Characterize potential sources of
water to support In Situ Resource Utilization (ISRU) for eventual human
missions. At this time it is not known where human exploration of Mars
might occur. However, if ISRU is determined to be required for reasons
of mission affordability and/or safety, then the following measurements
for water with respect to ISRU become necessary (these options cannot be
prioritized without applying constraints from mission system
engineering, ISRU process engineering, and geological potential):**

[Measurement Options:]{.underline}

a.  Perform measurements within the top few meters of the regolith in a
    location within the near-equatorial region (approximately ±30°) that
    the Mars Odyssey mission indicates is a local maximum in hydrogen
    content, to determine: (i) concentration of water released upon
    regolith heating, (ii) composition and concentration of other
    associated volatiles released with water, and (iii)
    three-dimensional distribution of measurements i & ii within a 100
    meter x 100 meter local region. This option would include water
    contained in hydrous minerals, as adsorbed water, and in any other
    form it might be present in the regolith. Either unconsolidated or
    loosely consolidated regolith is a focus of current attention
    because of the need to minimize mining engineering, but outcrops of
    rock containing hydrous minerals may also be a valuable possibility
    if they are sufficiently friable.

b.  Perform measurements to (i) identify and determine the depth,
    thickness, and concentration of water in subsurface ice deposits to
    a few meters depth at approximately 40° to 55° latitude, (ii)
    determine the demarcation profile/latitude where near-surface
    subsurface ice formation does and does not occur.

c.  Perform measurements in the polar region (70º to 90º) to determine
    the depth, thickness, and concentration of near-surface water/ice.

Measurements for water at other locations and depths are not precluded
but would require further scientific measurements and/or analysis to
warrant consideration. This option would specifically include accessing
a deep aquifer.

*[The following investigations are listed in descending priority
order.]{.underline}*

**[2. Investigation.]{.underline} Determine the possible toxic effects
of Martian dust on humans.\
**[Measurements:]{.underline}

a\. For at least one site, assay for chemicals with known toxic effect
on humans. Of particular importance are oxidizing species (e.g., CrVI).
(May require Mars Sample Return (MSR)).

b\. Fully characterize soluble ion distributions, reactions that occur
upon humidification and released volatiles from a surface sample and
sample of regolith from a depth as large as might be affected by human
surface operations.

c\. Analyze the shapes of Martian dust grains sufficient to assess their
possible impact on human soft tissue (especially eyes and lungs).

d\. Determine if Martian regolith elicits a toxic response in an animal
species that are surrogates for humans.

**[3. Investigation]{.underline}. Assess atmospheric electricity
conditions that may affect TAO and human occupation.**

[Measurements:]{.underline}

a.  Basic measurements:

> DC E-fields: 0-80 kV/m, dV=1 V, bandwidth 0-10 Hz, rate = 20 Hz
>
> AC E-fields: 10 uV/m -- 10 V/m, Frequency Coverage 10 Hz-200 MHz, rate
> = 20 Hz, with time domain sampling capability
>
> Atmospheric Conductivity: 10^-15^ to 10^-10^ S/m, ds= 10% of local
> ambient value
>
> Ground Conductivity: \>10^-13^ S/m, ds= 10% of local ambient value
>
> Grain charge: \>10^-17^ C
>
> Grain radius: 1-100 μm

b.  Combine with surface meteorological measurements to correlate
    electric forces and their causative meteorological source for more
    than 1 Martian year, both in dust devils and large dust storms.
    Combine requirements for 1Bb with 3a above.

**[4. Investigation.]{.underline} Determine the processes by which
terrestrial microbial life, or its remains, is dispersed and/or
destroyed on Mars (including within ISRU-related water deposits), the
rates and scale of these processes, and the potential impact on future
scientific investigations.**

[Measurements:]{.underline}

a.  Determine the rate of destruction of organic material by the Martian
    surface environment.

b.  Determine the mechanisms and rates of Martian surface aeolian
    processes that disperse organic contaminants.

c.  Determine the adhesion characteristics of organic contaminants on
    landed mission elements, and the conditions and rates under which
    these contaminants are transferred to the Martian environment.

d.  Determine the mechanisms to transport surface organic contaminants
    into the Martian subsurface, and in particular, into a Martian
    aquifer, should such exist.

e.  Determine if terrestrial microbial life can survive and reproduce in
    the natural Martian environment.

**[5. Investigation.]{.underline} Characterize in detail the ionizing
radiation environment at the Martian surface, distinguishing
contributions from the energetic charged particles that penetrate the
atmosphere, secondary neutrons produced in the atmosphere, and secondary
charged particles and neutrons produced in the regolith.**

[Measurements:]{.underline}

a\. Measurement of charged particles with directionality. Identify
particles by species and energy from protons to iron nuclei in the
energy range 20-1000 MeV/nuc.

b\. Measurement of neutrons with directionality. Energy range from
[\<]{.underline}1 keV to [\>]{.underline}100 MeV.

c\. Simultaneous with surface measurements, a detector should be placed
in orbit to measure energy spectra in Solar Energetic Particle events.

**[6. Investigation.]{.underline} Determine traction/cohesion in Martian
regolith (with emphasis on trafficability hazards, such as dust pockets
and dunes) throughout planned landing sites; where possible, feed
findings into surface asset design requirements.**

[Measurements:]{.underline}

a\. Determine vertical variation of *in situ* regolith density within
the upper 30 cm for rocky areas, on dust dunes, and in dust pockets to
within 0.1 g cm^-3^.

b\. Determine variation in *in-situ* internal angle of friction for dust
dunes and dust pockets to within 1°.

c\. Determine regolith cohesion for rocky areas, dust dunes and in dust
pockets to within 0.1 kN m^-2^.

d.  Imaging to Mars Reconnaissance Orbiter High Resolution Imaging
    Science Experiment (MRO HiRISE) standards (30 cm/px) for selected
    potential landing sites.

For basic design of mobility systems, the following measurements would
be needed (not just at the dust pockets and dunes, but also on the
consolidated regolith surfaces where we might do most of the driving):
(i) rolling resistance (the torque that regolith applies to a rolling
wheel while driving), (ii) traction test (torque required to spin a
wheel while the rover is held stationary), and (iii) shape/size of the
resulting wheel ruts while driving normally.

*Note #11: These three things would probably be measured routinely on
all Mars rovers.*

*Note #12: ISRU excavation could require hauling larger loads
(regolith/ice payload) than what we have ever hauled in the past.
Therefore they would need these data to properly design wheels and
chases (e.g., rover and large structure mobility systems), avoiding
energy-wasteful designs or risk of getting bogged down.*

**[7. Investigation.]{.underline} Determine the meteorological
properties of dust storms at ground level that affect human occupation
and EVA.**

[Measurements:]{.underline}

a.  Pressure (P), temperature (T), velocity (v), and dust density
    (opacity) as a function of time at the surface, for at least a
    Martian year, to obtain an understanding of the possible
    meteorological hazards inside dust storms. Surface package measure
    directly:

> Same as requirement for 1Bb with added
>
> Dust size: 1-100 μm
>
> Dust density: 2-2000 grains/cc

b.  Orbiting weather station: optical and infrared measurements to
    monitor the dust storm frequency, size and occurrence over a year,
    and measure terrain roughness and thermal inertia. Climate sounder
    would enable middle atmosphere temperature measurements. *In situ*
    density or spacecraft drag sensors could monitor the dust storm
    atmosphere inflation at high altitudes. Same as requirement 1Bc.

Table 1. Summary of Location Considerations for high-priority human
Precursor Investigations.

+----------------+----------+--------------+-----------+--------------+
| Investigation  | Needed   | Measurements | Mea       | Measurement  |
|                | once at  | at multiple  | surements | at the human |
|                | Mars     | sites        | over time | site         |
+----------------+----------+--------------+-----------+--------------+
| 1Aa-b. Basic   | ### X    | **?**        |           |              |
| dust/regolith  |          |              |           |              |
| properties     |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 1Ac. Airborne  | ### X    | ###          |           |              |
| dust in dust   |          |              |           |              |
| storms         |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 1B.            | ###      | ### X        | ### X     |              |
| Atmospheric    |          |              |           |              |
| variations     |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 1Ca.           | ### X    | ###          | ###       | ###          |
| Biohazard -    |          |              |           |              |
| dust           |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 1Cb.           | ###      | ###          | ###       | ### X        |
| Biohazard -    |          |              |           |              |
| site specific  |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 1D. Water for  | ###      | ### X        | ###       | ### X        |
| ISRU           |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 2\. Dust       | ### X    | ###          | ###       | ###          |
| toxicology     |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 3\.            | ###      | ### X        | ### X     | ###          |
| Atmospheric    |          |              |           |              |
| electricity    |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 4\. Forward    | ### X    | ###          | ### X     | ### ?        |
| Planetary      |          |              |           |              |
| Protection     |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 5\. Ionizing   | ### X    | ###          | ### X     | ###          |
| radiation      |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 6\. Terrain    | ### X    | ### ?        | ###       | ### ?        |
| trafficability |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+
| 7\. Dust       | ### X    | ###          | ### X     | ###          |
| storms         |          |              |           |              |
+----------------+----------+--------------+-----------+--------------+

**[B. Objective]{.underline}. Conduct risk and/or cost reduction
technology and infrastructure (T/I) demonstrations in transit to, at, or
on the surface of Mars.**

Technology validation on Mars flight missions and infrastructure
emplacements are needed to reduce the risk and associated uncertainty
inherent in new, unproven technologies and to reduce the cost of human
Mars exploration. These demonstrations were chosen for Mars robotic
flight missions based upon: (a) their high degree of interaction with
the Mars environment, (b) their anticipated large leverage on human Mars
mission architecture feasibility, and (c) uncertainty of whether Earth,
Earth-orbit or lunar testing would supply sufficient data to reduce risk
and cost, or increase performance of these systems.

Prioritization Criteria

The following criteria were used, assuming a series of robotic flight
missions preceding the first human mission, to establish the priority of
importance, when the validation should be done and whether or not the
validation must be done on a Mars mission:

Priority: The anticipated magnitude of the risk and/or cost reduction of
human missions to Mars.

Timing: The likely timing of the technology flight mission needed
relative to the first human mission:

Early: to influence architecture decisions (14 to 20 years prior)

Mid: to influence mission and flight system design decisions (8 to 12
years prior)

Late: to influence operability decisions (4 to 6 years prior)

Venue: Some technology validations could be accomplished less
expensively and more comprehensively on other than Mars missions.
Required technologies were therefore grouped according to whether they
could best be performed (in decreasing order of cost) :

a, At or in transit to/from Mars

b\. On the Moon

c\. In Earth orbit

d\. On Earth

Only those technology and infrastructure items requiring demonstration
at Mars, 3a, are listed below as candidates for Mars human precursor
missions. Those not requiring development and demonstration on Mars
missions, 3b,c and d, are prioritized and described in the associated
white paper. Additionally, a set of suggested near-term systems studies
has been defined which will, when completed, enable refined definition
and prioritization.

The following is a prioritized grouping 1 through 3; there is no
sub-prioritization within the groups.

**[1A. Demonstration.]{.underline} Conduct a series of three aerocapture
flight demonstrations:**

70° sphere cone shape (robotic scale) to demonstrate aerocapture at Mars
(Early).

New entry vehicle configuration suitable for human exploration (robotic
scale) aerocapture at Mars (Mid).

New entry vehicle configuration suitable for human exploration (larger
scale, end-to-end mission sequence) aerocapture at Mars (Late).

A primary challenge of flight missions to Mars is decelerating the
incoming spacecraft. There are four primary options:

Chemical propulsion

Aerobraking

Direct entry

Aerocapture

Given the expected mass of proposed human missions, the estimated
required mass of propellant to use Option #1 is large---this could lead
to severe cost and operational problems. Aerobraking (Option #2) is the
approach in which multiple orbits are used, extending over months, to
gradually lower the apoapsis as was done on the Mars Global Surveyor
(MGS) and Odyssey missions. The disadvantage of using this for human
missions is that it takes considerable time, which is likely to be
incompatible with other constraints on the proposed human mission.
Direct entry (Option #3), as used by Pathfinder and Mars Exploration
Rover (MER) missions, is at the extreme variation of aeroassist in which
entry capsules are decelerated to the point of parachute deployment.
However, the \"g\" forces involved in direct entry are excessive
relative to human tolerance. Aerocapture (Option #4) is an intermediate
form of aeroassist in which the vehicle is captured into low Mars orbit
on the first atmospheric pass. Aerocapture requires accurate navigation,
attitude control, and an effective aeroshape design. It is thought that
it would take three successful flight missions to demonstrate this
technology to a level of confidence that one would be prepared to use it
on a human mission.

**[1B. Demonstration.]{.underline} Conduct a series of three in-situ
resource utilization technology demonstrations:**

\(1\) ISRU Atmospheric Processing (Early)

> 1\. Demonstrate acquisition and separation of atmospheric resources
> for life support and propulsion/fuel cell power systems. Demonstrate
> production and storage of critical mission consumables (oxygen, fuel,
> life support gases, etc.).
>
> 2\. Preliminary Experiment Requirements: Mass \<25 kg; Power \<50 W;
> Production rate \>20 gm/day O~2~ or O~2~ fuel.
>
> 3\. Duration \> 30 sols.

\(2\) ISRU Regolith-Water Processing (Early)

> 1\. Perform excavation of Mars regolith down to 2 meters and
> demonstrate regolith handling and transport capabilities to regolith
> processing unit. Perform *in situ* measurements to support design of
> robotic and human scale excavation systems. Perform regolith
> processing to extract and separate water from the regolith in multiple
> batches to obtain TBD ml of water. Perform *in situ* measurements of
> the water and volatiles released during processing. Perform processing
> on the water to produce oxygen, hydrogen, and methane.
>
> 2\. Requirement for mobility is dependant on results from '07 Phoenix
> and '09 Mars Science Laboratory (MSL) missions.
>
> 3\. Preliminary Experiment Requirements: Mass \<30 kg; Power \<50 W;
> Production rate \>10 cm^3^/day of water.
>
> 4\. Duration \>15 sols.

\(3\) ISRU Human-Scale Application Dress Rehearsal (Late)

> 1\. The primary purpose of this demonstration would be to "buy down"
> risk by operating a complete end-to-end ISRU system (1/20 scale,
> duration 80 sols) culminating in a significant application such as
> producing propellants for a Mars Hopper, and the subsequent operation
> of the Hopper. An additional goal would be to make a first attempt to
> gather and utilize regolith for construction purposes, (e.g.,
> radiation shielding, at a small scale). This would be closely coupled
> to excavation, material transport, and beneficiation techniques
> derived from Regolith-Water Processing demonstration.
>
> 2\. Perform in conjunction with other human mission subsystems if
> possible, e.g., power system, fuel cell power system, oxygen/methane
> propulsion, landing hazard avoidance.
>
> 3\. Preliminary Requirements: 0.25 to 0.05 kg of O~2~-fuel/hr, Power
> 200 to 400 W.
>
> 4\. Duration 80 sols min.

It is not yet known when, if at all, ISRU would be a part of human
missions to Mars. However, ***if** ISRU is to be fully assessed,* these
demonstrations are considered to be required (i.e., they are considered
necessary to reach a decision to proceed or not with ISRU and constitute
yes/no gates). These demonstrations would need to be carried out in
parallel with Goal IVA Investigation #1D, which relates to discovery and
characterization of the water deposits.

Currently there are no criteria for where human exploration would occur
on Mars. If ISRU is a potentially enabling factor in affordability or
safety, then resource location and feasibility would be a driver in site
selection. Alternatively, if a negative decision regarding ISRU were to
be made on the basis of relative cost or risk alternatives, then these
demonstrations become moot.

In addition to the exploration-related questions in Goal IVA-1D, the
practicalities of implementing ISRU are serially dependent upon two
fundamental factors: 1). Is the potential resource \"economically\"
accessible, meaning can enough be procured at acceptable cost, to more
than offset the cost of bringing it from Earth? 2). Can sufficient
supplies of the end-product be produced, stored and transferred with low
risk? The most obvious uses of *in situ* resources are those that focus
on obtaining resources that, if they have to be launched from Earth, are
large mass, thus cost, drivers. Typically water, oxygen and fuels would
be leading candidates for ISRU. Water has immediate use as such for crew
life support and hygiene. It also would serve as a source for hydrogen
and oxygen. The atmosphere of Mars contains carbon dioxide, traces of
water vapor, and inert gases (useful for diluting atmospheric oxygen).
The carbon dioxide could be a source of oxygen and could be reacted with
hydrogen to make fuel.

**[1C. Demonstration.]{.underline} Demonstrate an end-to-end system for
soft, pinpoint Mars landing with 10 m to 100 m accuracy using systems
characteristics that are representative of Mars human exploration
systems. (Mid)**

Pinpoint landing systems for human exploration vehicles would be
required for two reasons: first, safety and secondly, risk mitigation.
It is likely that pre-positioned supplies and emergency abort systems
would be located on Mars prior to arrival of humans. Landing near such
assets would increase the likelihood of successfully accessing such in
an emergency and would enhance mission efficiency in non-emergency
situations. Second, it is likely that a site selected for human
exploration would be selected because there is a specific science
objective to be accomplished. If prepositioned assets could be
sufficiently localized that landing in proximity would increase the
probability of successful science accomplishment.

**[2A. Demonstration.]{.underline} Demonstrate continuous and redundant
*in situ* communications/navigation infrastructure (Early). Deploy in
full-up Precursor Test Mission (Late).**

Mission safety and effectiveness would require the development of high
band-width continuous and redundant communications. This support for
human mission could be met, for example, by a pair of
longitudinally-offset areostationary relay satellites.

**[2B. Demonstration.]{.underline} Investigate long-term material
degradation over times comparable to human mission operations. (Mid)**

Our current state of knowledge of the Mars environment is inadequate to
confidently design essential space systems to be used on the Martian
surface. These include EVA suits, habitats and ancillary systems,
including mobility.

It would be essential to verify the capability of materials under
consideration for Mars surface operations to tolerate long-term exposure
(years) to Mars environmental phenomena using coupon, component,
subsystem and system level tests on Mars. Phenomena include: radiation;
temperature extremes and cycles; wind; atmosphere chemical and
electromagnetic properties; regolith and dust chemical, mechanical, and
electromagnetic properties; and Mars biology (if any). An LDEF (Long
Duration Exposure Facility) should be considered (implied return of test
samples).

**[3. Demonstration.]{.underline} Develop and demonstrate accurate,
robust and autonomous Mars approach navigation. (Mid)**

This is a mission safety item. It would provide a backup/replacement to
Deep Space Network based terminal navigation for a mission time-critical
event (e.g., Mars Orbit Insertion (MOI) or aerocapture).

**C. Objective. Characterize the State and Processes of the Martian
Atmosphere of Critical Importance for the Safe Operation of Both Robotic
and Human Spacecraft** (***[not in priority order]{.underline}*).**

This objective focuses on atmospheric processes of importance for the
safe implementation of all spacecraft missions. These investigations
would yield the critical information necessary to improve the likelihood
of successful execution of missions in the Martian environment.
Investigations would seek to characterize the atmosphere from the
surface to 400 km altitude to support spacecraft landing, flight,
aerocapture, aerobraking, long-term orbital stability, targeting of
observations from orbit, and mission planning. Every effort should be
made to accommodate instruments that would address these investigations
on each spacecraft bound for Mars.

**1. [Investigation:]{.underline} Understand the thermal and dynamical
behavior of the planetary boundary layer.**

The lowest portion (\<5km) of the atmosphere can be highly turbulent.
Horizontal and vertical winds in this region represent a significant
risk to spacecraft EDL and the operation of aerial platforms (e.g.,
balloons and aeroplanes). Turbulence also transports heat, so would also
be a concern for thermal design. The turbulence is driven by thermal
contrasts between the surface and the atmosphere, and mechanical
interactions between the mean wind and the rough planetary surface. This
investigation is designed to probe the connections between surface
temperature, the modification of surface and air temperatures by aerosol
radiative heating, and the dynamical and thermal state of the lower
atmosphere.

**2. [Investigation:]{.underline} Understand and monitor the behavior of
the lower atmosphere (0-80km) on synoptic scales.**

Mars exhibits significant seasonal and dramatic, episodic changes in the
state of the atmosphere. Of great concern to the operation of surface
and near-surface spacecraft, and for aerobraking, aerocapture, or
aeropass maneuvers, is the onset of regional and global dust storms.
Atmospheric dust loading and sedimentation modulates available solar
energy at the surface and perturbs the density profile. The mechanisms
of storm development are unknown at this time, and thus current models
cannot predict them. Prediction would require significant additional
study of these events, while early observation would enable mission
engineers to prepare for the effects storms may have on mission
activities. It is critical for support of Mars missions that
continuously-operational, meteorological assets be maintained in Martian
orbit to improve our understanding of the processes so that we could
better predict atmospheric conditions at the time a spacecraft arrives
and to make observations near the time of entry.

**3. [Investigation:]{.underline}** **Determine the atmospheric mass
density and its variation over the 80 to 200 km altitude range.**

Aerobraking, aerocapture, and aeropass operations use the atmosphere as
a brake. These operations are safest when the drag imparted by the
atmosphere can be accurately estimated ahead of time. Unfortunately, the
Martian atmosphere exhibits substantial variations in density at a given
geometric height due to the influence of the diurnal cycle, seasonal
cycle, large-scale atmospheric circulation, and the propagation of
waves. Mapping and understanding the processes responsible for the
density variations in the upper atmosphere would be critical to
high-precision spacecraft trajectory planning. For example, techniques
for measuring and predicting the mass density on time scales of hours to
days are key requirements for aerobraking. This information would also
be important for mission planning (e.g., estimating the amount of fuel
needed throughout mission life).

**[4. Investigation:]{.underline} Determine the atmospheric mass density
and its variations at altitudes above 200 km.**

Knowledge of mass density variations at high altitudes is important for
precision targeting of orbital observations and for achieving long-term
orbital stability required to meet planetary protection constraints.

V. CROSS-CUTTING STRATEGIES

Analysis of the above goals, objectives, and investigations has led to
the formulation of several cross-cutting strategies that could be used
to guide the present and future exploration of Mars. These include:

**[Follow the Water]{.underline}**. In 2000-2001, at the time of the
formation of MEPAG and the establishment of the first version of the
Goals Document, it was recognized that water was a central aspect of
many of the high-priority objectives and investigations in each of the
four goals areas. MEPAG proposed the strategy of "follow the water" as a
means of simultaneously approaching multiple objectives.

-   For Goal I (Life), water (and in liquid form) is essential to life
    as we know it. Thus, finding past or present liquid water is our
    best starting point for the search for life.

-   For Goal II (Climate), water is one of the keys to understanding the
    climate system in the form of the polar caps, the seasonal movement
    of water into the atmosphere, atmosphere-crust interactions
    associated with the circumpolar permafrost belts, the progressive
    loss of water and other molecules from the top of the atmosphere,
    etc.

-   For Goal III (Geology), water plays a major role in many fundamental
    geologic processes that have formed and shaped the Martian crust,
    including volcanism, erosion, sedimentation, alteration/diagenesis,
    and glaciation.

-   For Goal IV (Preparation for Humans), water is a critical local
    resource needed for the support of human explorers.

This strategy served as a very important focal point of the Mars program
through the missions Mars Global Surveyor (MGS) (1996-2006), Mars
Odyssey (ODY) (2001-present), Mars Exploration Rovers (MER)
(2003-present), Mars Reconnaissance Orbiter (MRO) (2005-present), and
Phoenix (PHX) (2007-present). Although as of 2008 we have not completed
our analyses of water on Mars, it is generally considered that our
discoveries to date are sufficient to no longer warrant water as a
primary focal point for the program.

[**Understand Mars as a System**.]{.underline} By the end of 2004, with
extensive results from MGS, several years of data from ODY, and one year
of data from the two MER rovers, it was recognized that Mars is
significantly more diverse and complex than had been previously thought.
Thus, achieving a full understanding of Mars would require understanding
the primary components of the Martian system, and how they have
interacted with each other during different epochs of Martian history.
This strategy implies that we need to understand the diversity of Mars,
how that diversity originated, and the interconnectivity of the
different components.

[**Seek Habitable Environments**.]{.underline} Upon recognition that
Mars has a variety of different local environments, past and present,
and that these environments have different potential for habitability,
this cross-cutting strategy was proposed in 2008. Developing a
quantitative understanding of that habitability potential would require
investigations and measurements that span many of the aspects of Goals
I, II, and III. In addition, although Goal I relates to indigenous
habitability (and actual habitation), Goal IV relates to exogenous
habitability (i.e. habitability by human explorers). Thus, this strategy
applies to all four goal areas and is likely to become the primary focus
of Mars exploration efforts in the coming decade.

[^1]: MEPAG (2001), Scientific Goals, Objectives, Investigations, and
    Priorities, in [Science Planning for Exploring Mars]{.underline},
    JPL Publication 01-7, p. 9-38. Available on the web at
    http://mepag.jpl.nasa.gov/reports/index.html.

    ^2^ MEPAG (2004), Scientific Goals, Objectives, Investigations, and
    Priorities: 2003, G. J. Taylor, ed., 23 p. white paper posted
    07-16-04 by the Mars Exploration Program Analysis Group (MEPAG) at
    http://mepag.jpl.nasa.gov/reports/index.html.

[^2]: ^3^ MEPAG (2005), Mars Scientific Goals, Objectives,
    Investigations, and Priorities: 2005, 31 p. white paper posted
    August, 2005 by the Mars Exploration Program Analysis Group (MEPAG)
    at <http://mepag.jpl.nasa.gov/reports/index.html>.

    ^4^ MEPAG (2006), Mars Scientific Goals, Objectives, Investigations,
    and Priorities: 2006, 31 p. white paper posted February, 2006 by the
    Mars Exploration Program Analysis Group (MEPAG) at
    <http://mepag.jpl.nasa.gov/reports/index.html>.

    ^5^ Arvidson, R.E.,  Allen, C.C., DesMarais, D.J., Grotzinger, J.,
    Hinners, N., Jakosky, B., Mustard, J.F., Phillips, R., and Webster,
    C.R., (2006).  Science Analysis of the November 3, 2005 Version of
    the Draft Mars Exploration Program Plan.  Unpublished report dated
    Jan. 6, 2006, 13 p, posted January, 2006 by the Mars Exploration
    Program Analysis Group (MEPAG) at
    <http://mepag.jpl.nasa.gov/reports/index.html>.

[^3]: Regolith. As used in this document, a general term referring to
    the mantle of fragmental, unconsolidated to partially cohesive
    material, of any origin (*in situ*, residual, or transported) that
    nearly everywhere underlies the surface of Mars (after Glossary of
    Geology).

[^4]: [General Notes]{.underline}:

    *Except as noted, investigations are listed in priority order.
    Within each investigation, measurements are listed in priority
    order.*

    *[Prioritization Criteria]{.underline}:*

    *Magnitude of effect of precursor information on reduction of risk
    and/or cost of a human mission to Mars.*

    *Perceived degree of viability and cost of available mitigation
    options.*

    *Potential to obtain minimum necessary information in a less
    expensive way than by flying a mission to Mars.*

    *[Assumptions]{.underline}:*

    *The first human mission includes a landed human element.*

    *The possibilities of "short-stay" (\~30 sols) and "long-stay"
    (\~300 sols) are both under consideration, so the precursor program
    needs to support both.*