# **Session Summaries, 7th International Conference on Mars, July 9-13, 2007**

David W. Beaty, Charles J. Budney, and Daniel J. McCleese

August 10, 2007

# This report has been approved for public release by JPL Document Review Services and may be freely circulated. 

# **Recommended bibliographic** **citation:**

Beaty, D.W., Budney, C.J., and McCleese, D.J. (2007). Session Summaries,
7th International Conference on Mars, July 9-13, 2007. Unpublished white
paper, 22 p, posted August, 2007 by the Mars Exploration Program
Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>. JPL D-39753.

**INTRODUCTION**

The 7th International Conference on Mars, held July 9-13, 2007 at
Caltech, was organized into nine theme-oriented oral sessions (listed
below). Each of the oral sessions was configured with a set of papers of
relevance to the theme of the session, along with some introductory
comments by the session chairs to frame the session, and a concluding
discussion session that was moderated by the session chairs. The
following master discussion prompts were used for each of the concluding
discussion sessions:

-   **What do we know?**

-   **What do we need to learn next?**

-   **Are we doing the right things to find the answers?**

For each of the nine discussion sessions, the comments from the audience
were documented, and a primary purpose of this report is to present
those exchanges. In addition, because of the role played by the session
chairs in both framing these discussions and in moderating their flow,
they were given an opportunity to prepare a few paragraphs summarizing
their perspective on these questions.

#### [Technical Sessions and Session Chairs]{.underline}

**The distribution and context of water-related minerals on Mars**

Jack Mustard and Ray Arvidson

**Geology of the martian surface: Lithologic variation, composition, and
structure**

Hap McSween and Janice Bishop

**Water through Mars's geologic history**

Michael H. Carr and Ben Clark

**Volatiles and interior evolution**

Roger Phillips and Linda T. Elkins-Tanton

**The martian climate and atmosphere: variations in time and space**

S. W. Bougher & F. Forget

**Modern Mars: Weather, atmospheric chemistry, geologic processes, and
water cycle**

Rich Zurek and Leslie Tamppari

**The north and south polar layered deposits, circumpolar regions, and
changes with time**

Stephen Clifford and Wendy Calvin

**Mars astrobiology and upcoming Missions**

David Des Marais and Phil Christensen

**Martian stratigraphy and sedimentology: Reading the sedimentary
record**

Oded Aharonson and Scott McLennan

**SESSION SUMMARIES**

**1. The distribution and context of water-related minerals on Mars**

[**Session Chairs' Summary (**Jack Mustard and Ray
Arvidson)]{.underline}

This session consisted of 10 talks covering a diverse range of topics.
The first talk framed the session with the timeline of water-related
minerals on Mars derived from OMEGA data and integrated with the
geologic record derived from other mission data. Subsequent talks
focused on the new perspectives on phyllosilicate minerals made possible
with CRISM's high resolution views, details of sulfate and hematite
deposits in Valles Marineris, and the identification of phyllosilicate
minerals in the fluvio-deltaic deposits in Holden crater. Many of these
themes were carried forward in the poster session, with additional
perspectives offered from theoretical and experimental results.

The key hypothesis framing the session was that phyllosilicates were
dominantly formed during Mars' earliest period (Noachian), followed by
sulfates in the late Noachian to Hesperian. Since then, there has been
little evidence for formation of water-related minerals. This is despite
the abundance of morphologic features thought to be water related (e.g.
young valley networks and outflow channels, gullies, volcano-ice
interactions, and ice-related features).

For the phyllosilicate deposits, it is critical to determine if, and how
the composition of the deposits vary in space and time. This is central
to inferring the environmental conditions that existed at the time of
the formation of these minerals. Were they formed at the surface in
concert with an active hydrologic cycle or were they formed at depth in
a hydrothermal or warm, wet crust environment? Could they be the result
of magmatic water released from the cooling and crystallization of the
magma ocean? In order to understand these questions we need to have
carefully characterized deposits for which detailed stratigraphic and
superpositional relationships can be determined. Many of the
phyllosilicate deposits in the southern highlands are found in
association with impact craters (e.g. ejecta, walls, and central peaks).
A key question here is to what extent does the impact process stimulate
the formation of the phyllosilicates and to what extent are the observed
minerals passive tracers of the impact process? Impact melts may
actually be a source of the phyllosilicates, as opposed to exposing them
from lower, preexisting geologic units where water-rich impact melts
devitrify. Yet some of the largest phyllosilicate deposits are found
outside the obvious influence of impact craters (e.g. Mawrth Valles),
indicating that multiple formation processes are likely and need to be
understood.

The distinction between the phyllosilicate-rich Noachian and the
sulfate-rich late Noachian to Hesperian is an important observation. It
is imperative to identify regions where phyllosilicates and sulfates
co-occur. The environment of formation for the sulfates has benefited
from the success of MER, but the deposits found elsewhere need to
evaluated more carefully to understand if they are variations of the MER
models or due to other processes. For example, sulfate deposits do not
necessarily require surface water to form.

The issue of mineral abundance is a key technical question for the
community to consider. Development of approaches that combine the
visible-infrared-and thermal infrared wavelengths to determine modal and
lithologic mineralogy is important.

**[Notes from moderated discussion]{.underline}**

-   How do compositional variations occur, both in space and time?

-   Resolution of observations may be an issue...

-   We need to look for contacts between sulfates/phyllosilicates to
    determine the relationships, and for sampling both terrains --
    analogy to Apollo landing sites at geologic contacts

-   What's in the [rest]{.underline} of the rocks within (and outside
    of) sulfate/phyllosilicate units?

-   Work needs to be done to understand the geologic
    context/stratigraphic relationships of sulfates and phyllosilicates

    -   Why are these materials exposed in rims/central peaks of
        craters? Are they exposed, or formed, by these craters?

-   Earth analogues are useful for exploration of sulfate terrains,
    where we have abundant experience with similar deposits

-   There is a difference between observations of rock/water
    interaction, and evidence for the presence of water at the
    [surface]{.underline} of Mars

-   Gamma Ray data is telling us about varying chemistry of the crust

-   Largest exposure of phyllosilicates is in Mawrth Vallis -- and this
    is not in association with crater walls/peaks

-   Mineralogical changes record important, global changes within the
    Martian environment

    -   Sulfate terrains do not demand stable water at the surface

    -   Phyllosilicate terrains are the most likely to record the
        presence of surface hydrology -- look for the presence of
        carbonate grains here, to investigate atmospheric history

-   Impact melts may actually be the source of the phyllosilicates, as
    opposed to exposing them from lower, preexisting geologic units

    -   Contemporaneous divitrification, no subsequent alteration

-   Magmatic water/hydrothemal alteration may have played a significant
    role

-   Were phyllosilicates formed in the subsurface by alteration, or at
    the surface by deposition, and how do we resolve this?

**2. Geology of the martian surface: Lithologic variation, composition,
and structure**

[**Session Chairs' Summary (**Hap McSween and Janice
Bishop)]{.underline}

This session covered surface composition at a range of scales including
analysis of orbital data and rover data. Two talks described what the
Spirit rover has revealed. When viewed at this scale, the crust in Gusev
crater is seen as a complex assortment of alkaline volcanic rocks (all
related through fractional crystallization) and partially to completely
altered materials sometimes showing extreme chemical fractionations.
Four presentations then dealt with thermal emission spectra of the
Martian surface. New interpretations of TES and THEMIS data reinforce
the conclusion that the basaltic crust is mineralogically heterogeneous,
although there is still considerable debate about whether TES surface
type 2 material represents differentiated igneous rock (andesite) or
altered rock surface compositions (probably dominated by silica). One
paper then described models for impact melt generation and global
dispersal that suggest that glasses should be a significant component of
the surface materials. Finally, four presentations described the
geologic and stratigraphic context for phyllosilicates in ancient
Martian terrains, using hyperspectral VNIR data from OMEGA and CRISM
images and high-resolution surface views from HiRISE and HRSC. The
session ended with a lively moderated discussion.

What do we know:

We now know that the crust of Mars is dominated by basaltic volcanism,
and that aqueous alteration (chemical weathering) occurred early in Mars
history but weathering in more recent times has been mostly physical.

What do we need to learn next:

We need to understand the degree to which igneous fractionation has
occurred, i.e. is TES surface type 2 material andesitic or altered. The
concensus may be growing that it is altered and that Mars is a
basalt-covered world, but discussion continues on this. TES and THEMIS
analyses are using expanded wavelength coverage for modeling and
comparison with lab data that is enabling mapping of four surface types
with more precise spectral character. Additional work is needed in
comparing the OMEGA and CRISM results with the TES and THEMIS results in
order to gain a more complete picture of the global surface composition.

We need to understand how the phyllosilicates seen by OMEGA and CRISM
formed. Were they really formed during a warmer, wetter period of less
acidic alteration in the Noachian, or could they have formed and been
exposed by large cratering events that set up hydrothermal systems? This
requires more detailed mapping of phyllosilicates, including variations
in the types of phyllosilicates present, the kinds of minerals they are
associated with (e.g. mafic minerals such as olivine and pyroxene, or
others such as iron oxides/oxyhydroxides, sulfates, carbonates...), and
the kinds of structural features they are associated with (e.g. craters,
flow features, ridges, etc.).

We need to quantify the amounts and distributions of glasses (igneous
and impact-melted) on the Martian surface, and understand what may have
modified their spectral characteristics. Coordinated VNIR and thermal
spectral analyses may be able to contribute towards improved mapping of
glass and altered glass on the surface.

We have a broad geochronological outline, but we need appropriate tools
for absolute and relative dating of surfaces on Mars.

Are we doing the right things:

Yes, but more attention must be paid to understanding the geologic
context of alteration and magmatism, now that we have spectral
information that is nearly on the same scale as imaging.

We need structural information on the crust, which is mostly an untapped
area of concern.

We need to resolve the chronological questions associated with crater
counting on Mars, and we need absolute calibration points for crater
counts.

**[Notes from moderated discussion]{.underline}**

-   How can we tell primary basalt from altered basalt? What are the
    limits of TES in doing so? (Note: our ability to do this may vary
    from place to place)

-   Finding basalt and phyllosilicate or other alteration minerals
    adjacent to one another is critical

-   Do metamorphic rocks exist on Mars and are they being excavated by
    impact craters?

-   Critical to consider the information that different instruments give
    us from different depths, e.g. latitude dependency in upper hundred
    microns to 10s cm (TES vs. GRS info)

-   What happens in a big impact on Mars? Difficult because we have no
    Earth analogs and hard to separate from volcanic processes. How do
    we unravel? Look at young impact craters in volatile-rich regions.
    Looking at old and young impact craters

-   How confident can we be of mapping the silicon value derived from
    GRS?

-   Can we look for additional clays by combining information from OMEGA
    and GRS? Something hydrated beneath the dust or hydrated dust?

-   "Holy grail" may be a location with both sulfate and clay allowing a
    traverse across both -- how well could MSL do this? ChemCam can
    remotely remove weathering layers and assess underlying composition

-   Measurements made by the instruments are probably not wrong. We need
    to be more creative with combining the data sources (along with
    laboratory work) in order to interpret them. More MFR funding,
    perhaps?

**3. Water through Mars's geologic history**

[**Session Chairs' Summary (**Michael H. Carr and Ben
Clark)]{.underline}

The session on "Water Through Mars' Geologic History" included a variety
of approaches for attacking this multi-faceted question. Ten papers
covered approaches ranging from field analogs of geomorphological
features and chemical analogs of acid sulfate lakes, to laboratory
analyses of martian meteorites and in situ analyses of chemistry and
mineralogical constituents on Mars. This kaleidoscope of diverse
methodologies provided an excellent sampling of the tools which may be
brought to bear upon the complex history of water on Mars.

The perception that water has played a prominent role in the evolution
of Mars stems largely from interpretation of the morphology of the
surface. Extensive areas of dissected terrain suggested that, at times
in the past, conditions at the surface were such as to permit liquid
water to flow across the surface and erode the observed valleys. Until
recently this interpretation appeared at odds with the absence of
hydrated minerals, the abundance of easily weathered minerals, such as
olivine, and climate models. The big question still remains: Was there
was ever a global hydrologic system in which precipitation,
infiltration, runoff and groundwater flow were in quasi equilibrium with
evaporation and sublimation from large bodies of water and ice. Two
papers directly address this issue. Howard et al examine the pattern of
dissection by valley networks for clues as to the hydrological
conditions under which they form, and Benison et al emphasize the role
of very acid water in formation of the valleys which has implications
for the source of the water.

Another morphological puzzle is the role of water in surface processes
on present day mars. Gullies and other slope features appear to be
forming at the present day, and liquid water may be playing a role,
although this is difficult to reconcile with present-day conditions. The
paper by Head et al. suggests that dark slope streaks have close analogs
in Antarctica where similar streaks form by the melting of ground ice
and flow of the meltwater downslope beneath a dry surface layer.
Darkening is caused by wicking of moisture up to the surface.

The paper by McCubbin and Nekvasil sought to constrain the history of
magmatic volatiles in the Chassigny maritan dunite, tracing both H2O and
halides. Greenwood et al. proposed new constraints on martian H2O
reservoirs by examining D/H isotope ratios in apatite grains of martian
meteorites to infer major fractionation very early in Mars history,
attributable to hydrodynamic escape, followed by low loss rates over the
majority of geologic time with H2O trapped as ice.

Through a study of acid lakes in Chile and Australia, coupled with
laboratory experiments, Benison et al. are conducting wide-ranging tests
of chemical environments and mineralogical consequences. The uptake of
H2O from the atmosphere by Mg-sulfates is under laboratory investigation
by Vaniman et al, who describe known as well as newly discovered phases
and uptake-desorption phenomena. As reported by Goetz et al., Clark et
al., and Yen et al., elemental and mineralogical data from the Mars
rover missions have revealed both low and high water-rock ratio
alterations on Mars.

What do we know?

The history of water on Mars appears to span, literally, the whole of
geologic history. It pervades the magmas, has formed evaporitic
sandstones as well as nearly pure salt and silica concentrations, yet
has only slightly reacted with the wide-spread contemporaneous
fine-grained soils. Under today's conditions, it reacts with salts and
possibly some silicates.

What do we need to learn next?

Further information on the diversity of salt compositions is welcome.
Exploration by in situ measurements at Columbia Hills implicates not
only ferric and Mg sulfates, but also Ca sulfate, Ca phosphate, and Al
sulfate. The stratigraphic sequence of these deposits and their source
materials is currently unknown.

What do we need to do?

Continued exploration by MER rovers, at both sites, could further
elucidate the H2O history of these modified terrains. Laboratory studies
of H2O interactions with igneous source material (including acidic
conditions) as well as appropriate field studies will help reveal the
amounts of H2O and environmental influences in past martian surface
history. Further study and monitoring of the enigmatic gullies and slope
streaks on Mars are needed to understand the driving forces for their
formation and evolution. Sample return from areas which clearly contain
alteration products of H2O exposure can afford the opportunity for
laboratory investigation of materials not now, and unlikely to ever be,
in the martian meteorite record.

**[Notes from moderated discussion]{.underline}**

-   We have an awful lot of geochemical and geomorphologic data. How can
    we put it all together?

-   We need to better understand the geologic context of observations
    from small areas

-   Several processes have been proposed to explain the different
    geochemical evidence (volcanism, hydrothermal dissolution and
    deposition, weathering, groundwater circulation, evaporation). How
    do we determine what is going on where

-   What is causing the large chemical gradients in the top meter or so?
    What are the roles of fumarolic activity, acid fogs, liquid water?

-   On earth, you can get tremendous diversity geochemically from
    volcanic processes

-   When you consider where/when Gusev is, you must consider impact
    processes as well as volcanism.

-   Aqueous activity at a wide range of fluid composition ? high pH
    mixing with low pH

-   See similar heterogeneities in acid lake deposits in Australia

-   Distribution of Pasa Robles lighter material is very spotty which
    may be indicative of impact or fumarole origin

-   Low water/rock ratios at Gusev ? details of the elemental ratios can
    have a dramatic impact on the final evaporitic product

-   Meridiani may not have as low water/rock ratios

-   pH conditions in hydrothermal vents in 60 impact craters -- were all
    very high pH.

    -   Could help distinguish between impact/volcanic origins

-   Much of chemical diversity at Gusev is just beneath the surface

-   Silica deposits and sulfate deposits are hydrated and appear to be
    found in local lows.

-   Working model: dissolution and reprecipitation of aqueous systems.
    Volcanic and volcanoclastic because it seems too intricate to be an
    impact process

-   If slope streaks are indicative of liquid water, might they be
    classified as special regions?

-   HiRISE sees some topography associated with slope streaks supporting
    the dry avalanching theory

    -   DEM model of one of the deposits and the slope is very steep so
        you can have dry flow

-   History of water on Mars from D/H ratio

-   If water was lost at 4.5Ga, there would have been an influx of more
    water to explain geomorphology

-   Is it possible to explain the extreme D/H ratios by invoking very
    little communication between atmosphere/water reservoir?

-   Current state of what we know/don't know about ancient martian
    oceans/seas/standing water

    -   Period(s) of formation of valley networks may have been short.
        Landscape is not totally dominated by water erosion features

    -   When we talk about water, what do we imply by the composition of
        the water? Is it dilute or was it very salty/acidic?

    -   Debate on whether or not we need rainwater or if groundwater is
        sufficient

    -   Drainage patterns show that in many places it could not have
        been groundwater

-   Some basic geomorphic features are still ambiguous

-   Obliquity changes and consequences of snowfall and erosion at the
    equator

-   True polar wander paper ? what do we think about the recent paper?

    -   What shoreline feature? Are we tying together different features
        into a single shoreline?

    -   look at the duration of some of the features to see if
        conditions were a small episode or represented hundreds of
        millions of years.

**4. Volatiles and interior evolution**

[**Session Chairs' Summary (**Roger Phillips and Linda T.
Elkins-Tanton)]{.underline}

The focus of the workshop was naturally on current mission data, which
largely concerns surface features and compositions and volatile budgets.
Mars has remnants of an ancient surface, for more than does the Earth.
Mars therefore gives us an opportunity to link processes of formation
and internal processes to surface features and compositions perhaps more
directly than on Earth. A number of researchers are addressing problems
of internal evolution and links to surface manifestations. We now have
several models for early accretion and differentiation, production and
longevity of a core dynamo, production of basaltic crust, and
partitioning of initial and secondary volatile contents into the
atmosphere (with their effects on climate) and loss to space. Each of
these topics informs and is informed by remote sensing and rover data.
We hope interdisciplinary collaborations become richer as models become
more sophisticated and specific and as mission data continue to come in.
The atmosphere, hydrosphere, solid parts of the planet, and the core are
a coupled system. The framework for the origin and evolution of life on
Mars can only be understood within this context of "Mars System
Science." In future, geophysical measurements of the planet, most
particularly seismic and heat flow measurements, would greatly further
our basic understanding of Mars as we do not know with any precision the
basic compositional layering of the planet, its present thermal state,
and its energy potential for driving tectonic, volcanic, and atmospheric
processes.

**[Notes from moderated discussion]{.underline}**

-   What are the questions from the data coming from the missions in
    terms of physics and chemistry of internal processes?

-   How big is the core and what is the volume of the crust? Geophysical
    measurements that would be most valuable include:

    -   Seismology---would help define the depth of the olivine
        transition in the mantle, the nature and depth of the
        core-mantle boundary, the lithospheric depth, and regions of
        activity in the planet; and

    -   Heat flow---to constrain temperature profiles and modes of heat
        transport in the planet, as well as lithospheric thickness.

-   How iron rich and aluminum poor is the mantle? What are the physical
    implications not based on the Martian meteorites?

-   What are the structures and compositions of the Martian crust?

-   We have made significant and positive progress in answering some but
    not all of these questions on the nature of the Martian interior and
    geologic history.

-   Global average of potassium and thorium of Mars is double that of
    the Earth---iron is higher on Mars -- these are fundamental
    properties of the planet that originated at accretion and indicate
    first-order differences in terrestrial planet formation.

-   Early history---we don't see it all---infill of the Utopia Basin,
    for example, obscured older crust.

-   Potential for plate tectonics in early history---do the magnetic
    signatures indicate early plate tectonics or not? Is that question
    put to bed?

-   Gamma ray data indicates a large diversity of the composition of the
    crust; we need to differentiate alteration processes from primary
    igneous processes.

-   We need chronology of the earliest crust of Mars.

-   Some researchers maintain that there is nothing older than 4.0 Ga
    visible on Mars, that the Late Heavy Bombardment that affected the
    Moon so clearly must also have obliterated older records on Mars.

-   Rocks on the Moon preserve the record earlier than 4.0, therefore
    the question for Mars is not whether there is older material, but
    simply how large it might be: Hand-sample? Terrane?

-   If sample return occurs it should be planned to help determine the
    chronology of events on Mars.

-   What is the most valuable sample we can collect? Can we actually
    find a sample at the phyllosilicate and sulfate locations?

-   Can a dynamo last longer than a few hundred million years on Mars?

-   Plate tectonics-- crater chronology does not rule out plate
    tectonics earlier than 3.9 Ga. This would change the age constraints
    on the dynamo.

-   We have learned a fantastic amount from Martian meteorites, and will
    continue to learn more even from the samples we have. Antarctic
    searches should continue to be funded; we will almost certainly find
    additional unique samples, and this is far more cost-effective than
    planetary sample return, and faster.

-   What volatiles are (were) involved, besides water, in the martian
    hydrologic cycle? How can we determine this from remote sensing and
    *in situ* observations?

-   What is implied by the increase in elastic thickness over time for
    the evolution of interior volatiles?

-   Volatiles released into the atmosphere can perturb the climate --
    CO~2~, H~2~O, SO~2~, H~2~S, CH~4~. How important is this,
    particularly for the latter part of the Noachian? How important was
    Tharsis outgassing?

**5. The martian climate and atmosphere: variations in time and space**

[**Session Chair's Summary (**S. W. Bougher)]{.underline}

This session included papers and discussion focusing on past Martian
climate changes, present Mars climate and its variations over observable
solar cycle, inter-annual and seasonal timescales, and Mars upper
atmosphere climate features and their variability. Ancient Mars climate
changes are being investigated with the aid of multi-dimensional models
(i.e. volatile evolution studies) and various proxy indicators (e.g.
erosion rates and crater statistics). The present Martian climate (i.e.
lower atmosphere temperatures and the dust, water, CO2 cycles) is being
studied with measurements by successive spacecraft missions to the
planet (i.e. MGS, Odyssey, MERs, MEX, and MRO). This recent pattern of
monitoring is important to continue, and is contributing to the
development of a modern Martian climatology. Lastly, Mars upper
atmosphere measurements are not sufficient to define a modern
climatology. "Opportunity" science consisting of limited observations
(i.e. both spatially and temporally) is important to pursue and is
providing many fundamental discoveries that characterize the structure
and variations of the Mars upper atmosphere. In particular, recent
evidence shows that the Mars lower and upper atmospheres are coupled
thermally, dynamically, and chemically. GCM modeling frameworks are
evolving to properly capture the "whole atmosphere" coupling processes
that are required to explain these observed variations in the Martian
upper atmosphere.

It is clear that the monitoring of Martian lower atmosphere has been
very successful, and must be continued with future spacecraft missions
to the planet. A network of landed meteorology (MET) stations is also
needed to contribute essential "ground truth" to this monitoring
program. Boundary layer meteorology is also critical to address,
possibly with a MET network, but also with MET packages on all future
landers to the planet. The latter is a possibility that is achievable in
the near future.

Real progress on the development of a Mars upper atmosphere climatology
awaits a dedicated mission to address this region of the atmosphere and
its associated volatile escape rates. A final selection of an aeronomy
mission for the 2011 Mars Scout opportunity is clearly a giant step in
the right direction.

[**Session Chair's Summary (**Forget)]{.underline}

This first session on Mars present and past climate systems was very
diverse.

1)  A first part was dedicated to climate change on various timescale
    including the very long term (early Mars vs. today), the "periodic"
    climate changes resulting from orbital and obliquity planet
    parameters (with two talks dedicated to the low obliquity climate,
    to be completed with other talks presented in the polar cap sessions
    on Thursday morning), and the 10 to 100 years variations which may
    be apparent in the variations of the residual CO2 southern polar
    caps, for instance.

2)  A second part was focused on Mars upper atmosphere, thermosphere and
    ionosphere. Until recently, the Martian atmosphere between \~70 and
    200 km was very poorly known, with very little observations
    available. Now, the Mars Express SPICAM UV spectrometers and the
    accelerometer data obtained in-situ by MGS, MO, and MRO are
    providing unprecedented measurements which help to constrain this
    part of the atmosphere. These observations suggest that the current
    state of the art models are not yet able to reproduce and understand
    the observations...

The various talks had thus in common to raise a lot of questions and
enigma. The discussion focused on various aspects of the session:

-   Early Mars Climate models (e.g. Mischna et al. in the session) are
    now incorporating SO2, CH4, impacts influences in 3D models. More
    ongoing work will be at last published in the near future. Among
    many problems, an outstanding one is the calculation of the
    Greenhouse effect with relatively thick (\> 0.5 bar) CO2 atmosphere
    as possible on early Mars: CO2-CO2Collision induced absorption may
    play a key role in the radiative transfer, but there is little lab
    measurements available to calculate this accurately.

-   A usual question was raised : Where is the CO2 to give higher
    pressures in the past? The most likely answer seems to be :
    Atmospheric escape of all volatiles

-   A discussion was started about the suggestion by Paige et al. that
    low obliquity on Mars did not trigger a collapse of the CO2
    atmosphere into CO2 polar caps :

    -   "Even at 1mbar pressure, micrometeorites have to traverse
        significant atmosphere. Lack of micrometeorites doesn't rule out
        atmospheric collapse."

    -   There are current controversies about current population of the
        impactors. Uncertainties in scaling from Earth fluxes of
        micrometeorites, as well as larger sizes.

    -   Particle trajectory in low-pressure atmosphere over long
        distances. Where does confidence in this model come from?

    -   Optical measurements of bolides traveling through analogous
        regions of the Earth's atmosphere. Also some models exist. But
        for the smaller size ranges, the particles are stronger and less
        prone to breakup.

    -   Robust solution for past spin/orbit parameters are one thing to
        query. Also models of low-obliquity atmosphere.

    -   Components of CO2 condensation understood from present condition
        (somewhat). Other, less well-known components such as albedo
        variations exist.

    -   Simple models may over-predict amplitudes of variations in
        parameters like pressures.

-   Another part of the discussion was about Golombek et al. work on
    Erosion rates: "We don't know how long the rocks have been on the
    surface. Possibility of rocks being covered and exposed, not
    monotonic erosion".

-   The possibility of climate variations on the 100 years time scale
    (resulting in variations in the residual south CO2 caps, as well as
    variations in the occurences of planetary encircling dust storms,
    etc\...) suggested a question to the entire community: are there
    other surface clues that could help climate scientists to constrain
    these climates variations ?

-   One more enigma was recalled by Ann Sprague from the GRS team. The 6
    time argon enrichment (due to CO2 depletion) in the southern polar
    night cannot be reproduced by the numerous 3D models (GCM) that has
    tried so far !

**[Notes from moderated discussion]{.underline}**

-   Great diversity of topics, but in common: Lots of questions about
    past climate, atmospheric evolution, recent evolution, upper
    atmosphere.

-   Past climate models (e.g. Mischna) now incorporating SO2, CH4,
    impacts influences on early atmosphere.

-   Greenhouse effect on early Mars: Is collision induced adsorption
    included in paleo-GCM models? No lab measurements exist to solve
    this.

-   Low-obliquity climate: Budget of CO2 available for present and past
    climates. Total polar cap reservoir can only increase pressure
    slightly. Where is the CO2 to give higher pressures in the past?

    -   Atmospheric escape of all volatiles

-   Even at 1mbar pressure, micrometeorites have to traverse significant
    atmosphere. Lack of micrometeorites doesn't rule out atmospheric
    collapse.

-   There are current controversies about current population of the
    impactors. Uncertainties in scaling from Earth fluxes of
    micrometeorites, as well as larger sizes.

-   Particle trajectory in low-pressure atmosphere over long distances.
    Where does confidence in this model come from?

    -   Optical measurements of bolides traveling through analagous
        regions of the Earth's atmosphere. Also some models exist. But
        for the smaller size ranges, the particles are stronger and less
        prone to breakup.

-   Robust solution for past spin/orbit parameters are one thing to
    query. Also models of low-obliquity atmosphere.

    -   Components of CO2 condensation understood from present condition
        (somewhat). Other, less well-known components such as albedo
        variations exist.

-   Simple models may over-predict amplitudes of variations in
    parameters like pressures.

-   We have reasonably robust predictions, but we don't have
    understanding some of the finer details

-   Erosion rates: We don't know how long the rocks have been on the
    surface. Possibility of rocks being covered and exposed, not
    monotonic erosion.

-   Two models of Mars paleo-climate involving nitrates run: thin model
    / thick model. Both may give rise to nitrate formation. Nitrates
    should be present (observable). Sources for atmospheric gasses a
    necessary component to have isotopic ratios come out properly.

**6. Modern Mars: Weather, atmospheric chemistry, geologic processes,
and water cycle**

[**Session Chairs' Summary (**Rich Zurek and Leslie Tamppari, with
assistance from Michael Mischna)]{.underline}

The content of this session addressed contemporary weather on Mars
through explorations by present and recent spacecraft (MRO, MEX and MGS)
as well as through ground-based observations and numerical modeling.
Talks were of a highly diverse nature, but focused primarily on
atmospheric aerosols, the global water cycle and short-term change of
the martian surface.

It is apparent that the martian dust cycle (including quiescent years)
is highly variable, yet characterization of its behavior is critical to
future human exploration activities. Possible interruption of the MER
missions by a global-scale dust storm (July/August 2007) indicates the
important role dust will, and should, play in future mission design.
This also argues strongly for continued acquisition of atmospheric data,
ideally by every Mars spacecraft. Present orbiter coverage, due to
orbital restrictions, is limited to fixed local times, and it was noted
that expanded diurnal coverage would be a desirable capability of future
missions. One example of how to do this would be through a networked
mission with multiple landed stations. Additionally, the value of small,
simple atmospheric instruments (e.g. radio science data) was stressed.
An example of extracting value-added products from extant data was
presented, which outlined attempts to extract vertical profiles of dust
abundance from MGS TES data. The Mars Climate Sounder (MCS) can obtain a
similar product, lengthening our measurement baseline.

A significant outstanding question continues to center around the
presence of trace gases in the martian atmosphere, including water vapor
and methane. The detection of trace gases has been identified as a high
priority science question, and, indeed, MSO has been scoped to possibly
address this question. There is not universal consensus that this is the
best path to pursue with MSO, however. Numerous spacecraft-borne
instruments are currently capable of observing water vapor in the
martian atmosphere, including SPICAM, OMEGA and PFS on Mars Express and
MCS on MRO. What is consistent between these instruments is the
"back-end" inclusion of some level of atmospheric modeling, either
through radiative transfer calculations, or with full general
circulation models (GCMs). For the latter, it was demonstrated that the
assumptions made in the GCMs critically influence their results. For
example, the size and shape of a model's north polar residual cap
dictates how "wet" the model will be. Recent observations of the water
vapor content of the martian atmosphere suggest it may be drier than
previously assumed. GCMs are capable of reproducing this new, drier
state, however such capability reinforces the point that these models
are only as good as the assumptions that go into them. Subtle changes in
surface albedo introduced by the dust cycle may also reduce the water
abundance of the atmosphere. These time-varying changes ought to be
considered in future implementations of GCMs to provide more faithful
representations of the true atmosphere and surface.

The discovery of active gullies, as indicated by 'bright gully deposits'
(BGDs) is an exciting new discovery that shows the surface of Mars is
presently active. It remains uncertain whether BGDs are dry-based (mass
wasting) or wet-based (water flow), although laboratory experiments and
radiometric measurements to infer dust grain size can be used to
determine whether water is capable of generating these deposits under
martian environmental conditions.

**[Notes from moderated discussion]{.underline}**

-   Remaining issues

    -   Mismatch between modeling and data---need progress on both
        fronts

    -   Data: Near-surface atmosphere

        -   Surface-based networks

    -   Models: Boundary Layer processes, including surface-atmosphere
        exchange of dust and volatiles

-   What more do we need and why?

    -   Do we need longer-term data sets?

        -   Every Mars landing cycle is unique, more so in the dusty
            season

        -   Every Mars annual cycle we can get is a positive

        -   Characterization on a year-to-year basis is very important
            to human exploration

    -   Do we need expanded diurnal coverage?

    -   Do we need more tracers in the models? Integrated feedback?

-   Are we doing the right things to find the answers?

    -   Do we need a surface network? Concurrent with orbiter
        measurements?

    -   Should every lander have atmospheric capabilities? Which ones?

-   Surface humidity measurements are important and have not been done
    before PHX

-   More modeling of slices through atmosphere during different seasons

-   Will help answer whether or not the argon is concentrated close to
    the surface or is mixed with altitude

-   We've been rather unsuccessful in getting simple instruments with
    small data volumes on spacecraft. E.g., radio science

-   Long term measurements of wind magnitude and direction near the
    surface

-   Important for EDL and human exploration

-   How long is long-term?

-   Methane question - what is the status?

    -   Does the Mars community agree that this measurement is important
        and worth doing with MSO?

-   Trace gases are high priority, were defined as such in the past, and
    should be pursued again

-   What is the surface energy distribution of dust particles in the
    atmosphere? Are they very oxidizing?

-   What do we need to be able to discriminate between the dry or wet
    flow models for the bright gully deposits?

    -   More modeling and looking for BGDs in images

    -   More physical experiments under Martian conditions as to whether
        or not water can actually do that work?

-   Can measure albedo of bright deposits, we need to quantify how
    bright or dark these are. This will help constrain grain size

-   Are we still measuring gases in the Martian meteorites? Are we
    keeping up with the analyses of these trapped gases?

**7. The north and south polar layered deposits, circumpolar regions,
and changes with time**

[**Session Chairs' Summary (**Stephen Clifford and Wendy
Calvin)]{.underline}

As the planet's principal cold traps, the Martian polar regions have
accumulated extensive mantles of ice and dust that cover individual
areas \>10^6^ km^2^ and total as much as 3--4 km thick. From the small
number of superposed craters found on their surface, these layered
deposits are thought to be comparatively young---preserving a record of
the seasonal and climatic cycling of atmospheric CO~2~, H~2~O, and dust
spanning the past \~10^5^--10^8^ years. For this reason, the Martian
polar layered deposits (PLD) may serve as a Rosetta Stone for
understanding the geologic and climatic history of the planet.

The issues addressed by the ten talks presented during this session, and
the subsequent discussion, covered a wide range -- encompassed by the
following key questions[^1]:

-   What are the physical characteristics of the PLD and how are the
    different geologic units within, beneath, and surrounding the PLD
    related?

-   How old are the PLD? And what are their glacial, fluvial,
    depositional and erosional histories?

-   What are the mass and energy budgets of the PLD, and what processes
    control these budgets on seasonal and longer timescales?

-   What chronology, compositional variability, and record of climatic
    change is expressed in the stratigraphy of the PLD?

-   How have volatiles and dust been exchanged between polar and
    non-polar reservoirs? And how has this exchange affected the past
    and present distribution of surface and subsurface ice?

The talks by Y. Langevin, W. Calvin, and P. Thomas, addressed the
composition, properties, and general nature of both the seasonal and
residual polar ice caps based on their spectral characteristics and a
combination of both high-resolution and synoptic imaging. A much
different and larger-scale perspective on the nature of the PLD was
provided in the talks on the MARSIS (J. Plaut) and SHARAD (R. Phillips)
radar sounding investigations, which have provided a first look at the
basal topography and internal layered structure of both caps. Key
findings of these investigation include an no evidence of lithospheric
deflection beneath the caps or of basal melting -- observations which
suggest both a low geothermal heat flow and thick lithosphere.

Evidence that the south PLD once covered an area more than 1.5x its
present size was presented by J. Head, who discussed evidence that the
PLD experienced significant volcano-ice interactions that resulted in
the generation of massive amounts of meltwater during the Hesperian.

The obliquity-driven exchange of water between the planet's polar and
non-polar reservoirs was addressed by F. Forget, who noted that there is
now excellent agreement between the areas of deposition predicted at
high-obliquity by climate models and the geologic evidence for
glaciation at tropical and temperate latitudes associated with the
volcanoes in Tharsis. F. Montmessin argued that the loss of water from
such non-polar reservoirs at low-obliquity, and it cold-trapping at the
poles, was the most reasonable explanation for the origin of the
perennial water ice deposits discovered by the OMEGA instrument within
the South PLD.

Other evidence of the distribution of subsurface, and potentially
exchangeable, H~2~O was discussed during the presentations by J.
Banfield and M. Mellon. Banfield noted that an analysis of thermal
inertia data from the TES and THEMIS IR spectrometers, combined with
soil H~2~O column abundances derived from the Gamma Ray Spectrometer
(GRS) data, suggested that the local distribution of subsurface ice at
temperate latitudes exhibits considerable spatial heterogeneity,
although, on a broader scale, it appears reasonably consistent with the
distribution expected from atmospheric exchange. Mellon showed that the
geographic distribution and morphology of polygonally patterned ground
observed by the HiRISE instrument is also consistent with model
predictions, providing further evidence that the shallow subsurface of
Mars at temperate and polar latitudes may host a vast reservoir of H2O
that may be exchanges with other polar and non-polar reservoirs as the
obliquity of Mars varies.

Other point and questions that were raised during the subsequent
moderated discussion included:

**[Notes from moderated discussion]{.underline}**

-   There is a critical need for more lab experiments. Those that have
    been done to date have often failed to simulate reality, especially
    with regard to the physical properties of ice and how they affect
    the deposition process.

-   What is the density of the seasonal CO~2~ deposit and how does it
    vary over the caps?

-   How did the Polar Layered Deposits (PLD) form? How are the
    individual layers built? How do metamorphic processes affect the
    state of water ice? And how stable are the layers to sublimation and
    erosion?

-   We are near the limits of what remote sensing can tell us about the
    nature of the PLD. The future polar exploration should emphasize
    both the in situ analysis of multiple layers (by drilling, sending a
    cryobot to melt its way through the PLD, or traversing down a polar
    scarp with a rover) and sample return.

-   The residual ice caps are often discussed as if they were not
    connected to the underlying layered deposits. Perrhaps they are part
    of the same process?

-   To date, orbital radar sounding:

    -   Sees no evidence of lithospheric deflection beneath the polar
        caps, which may suggest the planet's current geothermal heat
        flow is very low. In situ measurements are needed.

    -   Indicates that the volume-averaged dust content of the polar ice
        must be low (\<20%) but there may be significant stratigraphic
        variability. May require in situ measurements.

    -   Has failed to reveal any evidence of current polar basal
        melting, which may be due to low heat flow. Basal melting in
        small local areas or under more favorable past conditions is not
        ruled out.

        -   Has also failed to detect any evidence of groundwater
            elsewhere on the planet. Various possible explanations exist
            (heat flux, lack of groundwater, detection limits of current
            instrumentation). Additional data is needed to discriminate
            among these possibilities.

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-   Currently observed changes in the extent of the South residual ice
    cap may be related to climate change, having implications for
    understanding and addressing the scientific and political aspects of
    this same issue on Earth.

-   Stratigraphy of PLD is believed to be correlated to climate
    variability, but this connection needs to be confirmed -- including
    relationship to orbital and short-term (decadal-scale and
    interannual) variations. Short-term variability is in particular
    need of further stud (e.g., why do slopes streaks appear more
    prevalent today than several years ago?).

-   There are no good geologic constraints on layer ages within the PLD.
    Should establish a geologic chronology independent of the inferred
    relationship to astronomically-induced climate change.

-   The current mass and energy balance of the PLD is one of the most
    critical unknowns. What is its relationship to geographic and
    temporal variations in albedo and deposition?

-   Trough formation may be rapid compared to other processes affecting
    the mass balance of the PLD, for this reasons they may be good
    targets for further study.

-   What roles do atmospheric variability and global weather patterns
    play in the evolution of the PLD?

    -   Need to make direct measurements of winds on Mars at multiple
        locations.

    -   Will require a meteorological network mission, including
        stations at the poles.

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-   (included above)

-   Relatively simple models do not explain the observed albedo--- need
    to combine interannual variability, atmospheric dynamics, and
    admixture of periodic dust storms.

-   (included above)Variability is observed on a wide range of scales
    and time frames. Need longer term observations to constrain decadal
    and interannual variability. Local scale variations (slope streaks)
    appear particularly erratic.

-   (included above) (included above)(included above)We need to
    understand atmospheric variability and weather patterns in order to
    begin to understand polar deposits

**8. Mars astrobiology and upcoming Missions**

[**Session Chairs' Summary** (David Des Marais and Phil
Christensen)]{.underline}

This session hosted five talks on astrobiology and six on future
missions. Regarding astrobiology, current missions have focused on
assessing the distribution and characteristics of environments, past and
present, that might have sustained microbial life, or still might do so.
Habitable environments must simultaneously provide not only liquid water
but also the necessary energy source(s) and biochemical ingredients.
Des Marais et al. concluded from observations by MER Spirit that
habitable environments might have existed in Gusev crater at least
intermittently in the distant past. Gibson argued from his global
assessment of the early history of Earth and Mars that ancient Mars must
have been habitable. C. McKay et al. outlined why the Martian polar
subsurface might be habitable even today and/or in the recent past.
Thomas-Keprta et al. presented microscopic observations of carbon and
iron species in ALH84001, indicating that ALH84001 and other meteorites
can continue to inform us about ancient Mars. Eigenbrode et al. reviewed
the value of crustal organic carbon inventories and compounds as
biosignatures and stressed their potentially enormous information
contents.

Regarding future missions, Conley and Race summarized our obligations
under international planetary protection treaties to maintain the
biological isolation between Earth and Mars and thereby also to preserve
Mars as an uncontaminated potentially second example of life. Aspects of
these obligations include appropriate spacecraft design and cleaning as
well as classification of regions on Mars regarding their potential to
sustain extant microbes. The Phoenix mission was summarized by Smith et
al. (overview), Tamppari et al. (atmospheric observations) and Arvidson
et al. (site selection). Phoenix is indeed an exciting opportunity to
understand the exchange of volatile species between the regolith and
atmosphere and to survey and characterize carbon and other life-relevant
compounds that might be sequestered in the ice. Golombek et al. and
Clegg et al. discussed site selection and the Laser Induced Breakdown
Spectroscopy for the 2009 Mars Science Laboratory mission. All of these
talks heralded the emerging age of Mars exploration where increasingly
sophisticated morphologic, mineralogical and chemical observations will
continue to unveil the evolution of Mars and its astrobiological
potential. Many of these themes were carried forward in the poster
session, with additional perspectives offered from theoretical and
experimental results.

This session indicated clearly that diverse, state-of-the-art
observations can and must continue at Mars, both in orbit and *in situ*,
in order to benefit fully from earlier findings and to extend the thread
of discovery. Significant further discoveries will become ever more
challenging to achieve but they will probably also become ever more
profound. Advances in remote sensing and spacecraft technology are
needed to improve site selection and site access. Capable *in situ*
science instruments are essential identify the very best samples to
include among those very few that can be returned to Earth. A key
science objective therefore will be to achieve a first MSR mission that
returns a diverse suite of carefully selected samples that will in turn
perpetuate and enhance this golden age of Mars exploration.

**[Notes from moderated discussion]{.underline}**

-   "Special Regions" are places on Mars that have the potential to
    sustain life either today or in the future. Any spacecraft that
    visits a special region must meet stringent planetary protection
    requirements to avoid forward biological contamination of the site.
    A set of criteria should be developed whereby regions on Mars could
    be assessed and, in perhaps many cases, exempted from "Special
    Regions" status.

    -   A spacecraft visiting a special region must be as clean as were
        the Viking landers.

    -   Future missions should assess the probability of life of Mars
        with an eye towards how risky it actually would be to send
        humans. We should locate landing sites that we can exempt from
        "Special Regions" designation.

    -   If we find out that there is no possibility of us contaminating
        Mars biologically, then the regulations will be relaxed
        significantly. (DJD comment: this is highly unlikely; it is
        virtually impossible to prove something of this nature.)

-   What precursor missions do we need before a sample return mission?
    What kinds of samples do we want/need to return? This is a crucial
    topic for ongoing dialog in the Mars science community.

-   According to Planetary Protection protocols, is MSR a prerequisite
    for a human mission?

    -   MSR is an extremely desirable requirement because its findings
        could enhance the human mission.

    -   Planetary Protection considerations would benefit from returned
        samples by perhaps increasing the probability that humans will
        be safe when they go, and by understanding the composition of
        the dust and its implications for spacecraft design.

    -   Would you prefer a sample from a special region? A range of
        opinions was expressed.

-   Organic detection limits were discussed both for spacecraft and in
    an Earth-based laboratory. What detection limits are practical on a
    spacecraft? Can we quantify it, for example for fatty acids?

    -   Realistic detection limits for flight instruments that are being
        developed will not be as low as what can be achieved in a
        laboratory on Earth.

    -   We will address certain sets of questions that can be addressed
        at a certain level of detection.

-   The ability to disentangle contamination from Earth is important,
    especially when you are dealing with very low detect limits. Modern
    flight instruments will probably detect Earth-based organic
    contamination during their missions.

-   What is the potential for studying slope streaks? pH? Water
    activity?

    -   The compositions of any fluids on Mars are important. Brines can
        be active at -60^o^C. Compositions can reveal fluid source
        regions, their history and their astrobiological potential.

-   Special regions-- recent developments have helped clarify the
    constraints

    -   Any extant fluids probably do not have the water activities that
        some had previously thought, therefore more places on the
        surface might not qualify as Special Regions.

-   Are we making the right measurements and developing the right flight
    instruments? Instruments on the landing missions should share more
    common ground with the types of instruments that we are using to
    find/pick the landing sites in the first place

    -   e.g., landed instruments doing spectroscopy in the VIS, NIR and
        MIR

-   What is our future strategy to obtain visual observations across a
    broad range of spatial scales?

    -   Remote sensing, surface cameras, microscopic imagers, true
        microscopes

    -   ExoMars and MSL would expand the range of scales

    -   What about missions beyond these?

**9. Martian stratigraphy and sedimentology: Reading the sedimentary
record**

[**Session Chairs' Summary** (Oded Aharonson and Scott
McLennan)]{.underline}

The 10 talks in the session were diverse in nature, but had a common
theme of understanding surficial processes and the sedimentary rock
record of Mars. Seven of the talks dealt with the sedimentary record at
Meridiani Planum, two with deposits at the Spirit landing site and one
examined cratering age analysis to date resurfacing history. In
addition, more than 30 papers in the various poster sessions also dealt
with these themes. The observational tools vary among physical,
morphological, geochemical and spectral and over many orders of
magnitudes in scale. These observations in turn provide a much firmer
foundation for various laboratory and theoretical modeling studies. The
recent explosion of high resolution data both from orbit and from the
ground allows probing the third dimension of martian crust, thereby
permitting the stratigraphic architecture of sedimentary deposits to be
better constrained and interpreted. In addition, it is clear that
integrating results from orbit with the detailed studies on the surface
and in the laboratory provide greatly increased understanding.

The general discussion that followed the formal session was wide-ranging
but largely focused on several important issues that face the study of
sedimentary environments on Mars. The major themes that came out of this
discussion included the following:

1\. Progress that has been made in understanding sedimentology,
stratigraphy and dating surfaces;

2\. Absolute and relative dating of the sedimentary record;

3\. Scales and nature of observations required for documenting
sedimentary materials on the surface (orbital and landed) and landing
site selection in sedimentary terrains;

4\. Issues associated with sample caching sedimentary materials both in
general and for MSL in particular;

5\. Issues related to characterizing and sampling sedimentary terrains
for sample return;

**[Notes from moderated discussion]{.underline}**

-   Progress being made in several areas, particularly: sedimentology,
    stratigraphy, age dating of surfaces using crater chronology.

-   Big Problem: In dealing with sedimentary sequences on Mars -- we
    cannot age date sedimentary rocks with any currently available
    techniques.

    -   They tend to be friable, erosion happens quickly.

    -   Even with nicely layered strata, the scale is too small to get
        good crater counting statistics.

-   Place particular emphasis on going to places and flying techniques
    which could tell us more about the age of sedimentary sequences.
    Selecting MSL site we should keep in mind sample caching.

    -   Some techniques for age dating may be available if these rocks
        ever come back to Earth.

-   We have an advantage on earth because of scale and fossil record,
    but even on Earth, absolute dating of the age of sedimentation
    directly from sedimentary sequences is cutting-edge.

-   Total mass to be returned from a sample return mission: Several
    hundred grams. What should we sample in the sites we're looking at
    now?

    -   With modern analytical capabilities, every sand grain can be
        considered as a rock.

-   Difficulties in using sample-return motivations for landing site
    selection. Currently, cache will stay on the rover. Perhaps cache
    should be dropped for later retrieval.

-   We are currently studying microscopic samples from Stardust mission,
    showing much information can be gained even from random samples

-   Samples to be cached, if returned to earth, will be the best
    pre-characterized samples of any planetary body yet.

-   We can do a lot (chemically, isotopically) with small samples. But
    to understand sedimentalogical information, **context** within
    texture of the deposit must be known.

-   Can you suggest a sampling criterion to distinguish between three
    hypotheses for Meridiani region formation?

    -   Texture-preserving samples (hand-sample sizes)

    -   Diagnostic mineralogy (XRD)

    -   mm-scale textures -- need chemical/mineralogical analysis on
        this same scale.

-   For sample return, just grains may not be enough. We seek
    'hand-sample' with context and textures.

-   Much of the evidence for diagenesis at Meridiani comes from MI
    images --scenes that are only a few cm across. These show effects of
    grain coatings, and mineral reprecipitation; information which would
    be lost in a powder.

-   MSR may be able to collect intact pieces of rock, rock chips,
    powder. Currently, MSL may only obtain powder.

-   Must think about 'requirements' and separate that from
    implementation. We have to be clever about in-situ observation,
    because return will be very expensive.

-   A good exercise: look at Meridiani and Gusev details and ask: what
    300g would we collect to maximize returns?

-   We have just found in the last few weeks at Gusev some of the most
    valuable rocks of the mission (Sol 1250). Per haps 50 x 10g samples
    would be a good representative suite from Gusev.

-   Jarosite has many possible stable isotopes, water isotopes included
    as well. Zircon is a very good mineral for dating.

    -   Getting one zircon grain can require sifting through large
        volumes of sample.

-   Current instrumentation to do in-situ petrography: micro-OMEGA,
    micro-TES, micro-Raman. Doing mm and sum-mm scale mineralogy
    imminent and desirable in order to pre-screen materials on the
    surface before selection for return.

-   Interpretation on Earth is never done using a single structure; we
    seek context and perspective. At Meridiani we invest significant
    resources in developing scenarios to reconstruct 3-d structures with
    adequate imaging. A single image of a sedimentary structure is
    ambiguous.

-   Victoria crater has allowed us to get orthogonal images of the same
    bed, allowing determination of a consistent paleo-flow direction.

-   At almost every promontory at Victoria we have acquired
    long-baseline stereo ranging constraining the topography of faces.

-   The 5th International Mars Conference was dominated by MGS results,
    the 6th dominated by Odyssey observations. In Mars 7 we have
    multiple platforms which overlap, looking at the same sites from
    multiple angles, filters, scales. We can now synthesize better
    interpretations.

-   MSL team is encouraged to set up imaging plans making the best of
    our experiences from Endurance, Home Plate, where 3-D stereo
    reconstructions have proven valuable.

-   Instrumental progress on miniaturized age-dating tools. MSL should
    be able to characterize grains as they go into the cache, so that we
    are able to evaluate the value of the samples in the cache.

[^1]: Originally identified by the participants in the 4^th^
    International Conference on Mars Polar Science and Exploration,
    Davos, Switzerland, October 2006.