***DRAFT\-- OPEN FOR COMMENTS***

*until after discussion at the MEPAG meeting of Feb. 20-21, 2008*

Science Priorities for Mars Sample Return

By the MEPAG Next Decade Science Analysis Group

MEPAG Next Decade Science Analysis Group (ND_SAG):

Lars Borg (co-chair), David Des Marais (co-chair), David Beaty, Oded
Aharonson, Steve Benner, Don Bogard, John Bridges, Charles Budney, Wendy
Calvin, Ben Clark, Jennifer Eigenbrode, Monica Grady, Jim Head, Sidney
Hemming, Noel Hinners, Vicky Hipkin, Glenn MacPherson, Lucia
Marinangeli, Scott McLennan, Hap McSween, Jeff Moersch, Ken Nealson,
Lisa Pratt, Kevin Righter, Steve Ruff, Chip Shearer, Andrew Steele, Dawn
Sumner, Steve Symes, Jorge Vago, Frances Westall

February 15, 2008

**[With input from the following experts:]{.underline}**

MEPAG Goal I. Anderson, Marion (Monash U., Australia), Carr, Mike
(USGS-retired), Conrad, Pamela (JPL), Glavine, Danny (GSFC), Hoehler,
Tori (NASA/ARC), Jahnke, Linda (NASA/ARC), Mahaffy, Paul (GSFC),
Schaefer, Bruce (Monash U., Australia), Tomkins, Andy (Monash U.,
Australia), Zent, Aaron (ARC)

MEPAG Goal II. Bougher, Steve (Univ. Michigan), Byrne, Shane (Univ.
Arizona), Dahl-Jensen, Dorthe (Univ. of Copenhagen), Eiler, John
(Caltech), Engelund, Walt (LaRC), Farquahar, James (Univ. Maryland),
Fernandez-Remolar, David (CAB, Spain), Fishbaugh, Kate (Smithsonian),
Fisher, David (Geol. Surv. Canada), Heber, Veronika (Switzerland),
Hecht, Mike (JPL), Hurowitz, Joel (JPL), Hvidberg, Christine (Univ. of
Copenhagen), Jakosky, Bruce (Univ. Colorado), Levine, Joel (LaRC),
Manning, Rob (JPL), Marti, Kurt (U.C. San Diego), Tosca, Nick (Harvard
University)

MEPAG Goal III. Banerdt, Bruce (JPL), Barlow, Nadine (Northern Ariz.
Univ.), Clifford, Steve (LPI), Connerney, Jack (GSFC), Grimm, Bob
(SwRI), Kirschvink, Joe (Caltech), Leshin, Laurie (GSFC), Newsom,
Horton, (Univ. New Mexico), Weiss, Ben (MIT)

MEPAG Goal IV. McKay, David (JSC), Allen, Carl ((JSC), Jolliff, Brad
(Washington University), Carpenter, Paul (Washington University),
Eppler, Dean (JSC), James, John (JSC), Jones, Jeff (JSC), Kerschman,
Russ (NASA/ARC), Metzger, Phil (KSC)

[Recommended bibliographic citation:]{.underline}

MEPAG ND-SAG (2008). Science Priorities for Mars Sample Return,
Unpublished white paper, 70 p, posted March 2008 by the Mars Exploration
Program Analysis Group (MEPAG) at
<http://mepag.jpl.nasa.gov/reports/index.html>.

[Correspondence authors:]{.underline}

Inquiries should be directed to David Des Marais
(David.J.DesMarais@nasa.gov, 650 604 3220), Lars Borg (borg5@llnl.gov,
925-424-5722), or David W. Beaty (<David.Beaty@jpl.nasa.gov>,
818-354-7968)

TABLE OF CONTENTS

[I. EXECUTIVE SUMMARY 1](#__RefHeading___Toc191123507)

[II. INTRODUCTION 4](#__RefHeading___Toc191123508)

[III. EVALUATION PROCESS 5](#__RefHeading___Toc191123509)

[IV. SCIENTIFIC OBJECTIVES OF MSR 6](#__RefHeading___Toc191123510)

[IV-A. History, Current Context of MSR's scientific objectives
6](#__RefHeading___Toc191123511)

[IV-B. Possible Scientific Objectives for a Next Decade MSR
7](#__RefHeading___Toc191123512)

[V. SAMPLES REQUIRED TO ACHIEVE THE SCIENTIFIC OBJECTIVES
13](#__RefHeading___Toc191123513)

[V-A. Sedimentary materials rock suite.
13](#__RefHeading___Toc191123514)

[V-B. Hydrothermal rock suite 14](#__RefHeading___Toc191123515)

[V-C. Low temperature altered rock suite.
14](#__RefHeading___Toc191123516)

[V-D. Igneous rock suite. 14](#__RefHeading___Toc191123517)

[V-E. Regolith 14](#__RefHeading___Toc191123518)

[V-F. Polar Ice 14](#__RefHeading___Toc191123519)

[V-G. Atmospheric gas 14](#__RefHeading___Toc191123520)

[V-H. Dust 14](#__RefHeading___Toc191123521)

[V-I. Depth-resolved suite 14](#__RefHeading___Toc191123522)

[V-J. Other 14](#__RefHeading___Toc191123523)

[VI. FACTORS THAT WOULD AFFECT THE SCIENTIFIC VALUE OF THE RETURNED
SAMPLES 14](#__RefHeading___Toc191123524)

[VI-A. Sample size 14](#__RefHeading___Toc191123525)

[VI-B. Number of Samples. 14](#__RefHeading___Toc191123526)

[VI-C. Sample Encapsulation. 14](#__RefHeading___Toc191123527)

[VI-D. Sample acquisition system priorities
14](#__RefHeading___Toc191123528)

[VI-E. In situ measurements for sample selection and documentation of
field context. 14](#__RefHeading___Toc191123529)

[VI-F. Temperature. 14](#__RefHeading___Toc191123530)

[VI-G. Diversity of the returned collection
14](#__RefHeading___Toc191123531)

[VI-H. Surface Operations 14](#__RefHeading___Toc191123532)

[VI-I. Documented Sample Orientation 14](#__RefHeading___Toc191123533)

[VI-J. Planning Considerations Involving the MSL/ExoMars Caches
14](#__RefHeading___Toc191123534)

[VI-K. Planetary Protection 14](#__RefHeading___Toc191123535)

[VII. Program Context, and Planning for the First MSR
14](#__RefHeading___Toc191123536)

[VIII. SUMMARY OF FINDINGS AND RECOMMENDED FOLLOW-UP STUDIES
14](#__RefHeading___Toc191123537)

[IX. ACKNOWLEDGEMENTS 14](#__RefHeading___Toc191123538)

[X. REFERENCES 14](#references)

LIST OF TABLES

[Table 1: Scientific Objectives, '03/'05 MSR, 2009 MSL, and 2013 ExoMars
(order listed as in the originals) 7](#__RefHeading___Toc191123496)

[Table 2 Planning aspects related to a returned gas sample.
14](#__RefHeading___Toc191123497)

[Table 3 Summary of Sample Types Needed to Achieve Proposed Scientific
Objectives. 14](#__RefHeading___Toc191123498)

[Table 4 Subdivision history of Martian meteorite QUE 94201
14](#__RefHeading___Toc191123499)

[Table 5: Generic plan for mass allocation of individual rock samples
14](#__RefHeading___Toc191123500)

[Table 6 Summary of number, type, and mass of returned samples.
14](#__RefHeading___Toc191123501)

[Table 7 Science Priorities Related to the Acquisition System for
Different Sample Types. 14](#__RefHeading___Toc191123502)

[Table 8 Rover-based Measurements to Guide Sample Selection.
14](#__RefHeading___Toc191123503)

[Table 9 Effect of Maximum Sample Temperature on the Ability to Achieve
the Candidate Science Objectives. 14](#__RefHeading___Toc191123504)

[Table 10 Relationship of the MSL cache to planning for MSR.
14](#__RefHeading___Toc191123505)

[Table 11 Science priority of attributes of the first MSR.
14](#__RefHeading___Toc191123506)

ACRONYM GLOSSARY

  ---------------- ------------------------------------------------------
  AMS              Accelerator mass Spectrometry

  APXS             Alpha Proton X-ray Spectrometer

  ATLO             Assembly, Test, and Launch Operations

  EMPA             Electron Microprobe Analysis

  ExoMars          A rover mission to Mars planned by the European Space
                   Agency

  FTIR             Fourier transform infrared spectrometer

  GSFC             Goddard Space Flight Center

  IMEWG            International Mars Exploration Working Group

  INAA             Instrumental Neutron Activation Analysis

  JSC              Johnson Space Center

  KSC              Kennedy Space Center

  LaRC             Langley Research Center

  MEP              Mars Exploration Program

  MEPAG            Mars Exploration Program Analysis Group

  MER              Mars Exploration Rover. A NASA mission launched in
                   2003

  MEX              Mars Express, a 2003 mission of the European Space
                   Agency

  MRO              Mars Reconnaissance Orbiter, a 2005 mission of NASA

  MS               Mass Spectrometry

  MSL              Mars Science Laboratory---a NASA mission to Mars
                   scheduled to launch in 2009

  MSR              Mars Sample Return.

  ND-MSR SAG       Next Decade Mars Sample Return Science Analysis Group

  OCSSG            Organic Contamination Science Steering Group, a MEPAG
                   committee

  PI               Principal Investigator

  PLD              Polar Layered Deposits

  PP               Planetary Protection

  SEM              Scanning Electron Microscopy

  SIMS             Secondary Ion Mass Spectrometry

  SNC Meteorites   The group of meteorites interpreted to have come from
                   Mars

  SRF              Sample Receiving Facility

  SSG              Science Steering Group. A subcommittee of MEPAG.

  TEM              Transmission Electron Microscopy

  TIMS             Thermal Ionization Mass Spectrometry

  VNIR             Visible/near infrared

  XANES            X-Ray Absorption Near Edge Structure

  XRF              X-Ray Fluorescence
  ---------------- ------------------------------------------------------

# 

[]{#__RefHeading___Toc191123507 .anchor}EXECUTIVE SUMMARYThe return of
Martian samples to Earth has long been recognized to be an essential
component of a cycle of exploration that begins with orbital
reconnaissance and *in situ* surface investigations. Major questions
about life, climate and geology require answers from state-of-the-art
laboratories on Earth. Spacecraft instrumentation cannot perform
critical measurements such as precise radiometric age dating,
sophisticated stable isotopic analyses and definitive life-detection
assays. Returned sample studies could respond radically to unexpected
findings, and returned materials could be archived for study by future
investigators with even more capable laboratories. Unlike Martian
meteorites, returned samples could be acquired with known context from
selected sites on Mars according to the prioritized exploration goals
and objectives.

The ND-MSR-SAG formulated the following 11 high-level scientific
objectives that indicate how a balanced program of ongoing MSR missions
could help to achieve the objectives and investigations described by
MEPAG (2006).

1.  
2.  
3.  
4.  
5.  
6.  
7.  
8.  
9.  
10. 
11. 

Determine the chemical, mineralogical, and isotopic composition of the
crustal reservoirs of carbon, nitrogen, sulfur, and other elements with
which they have interacted, and characterize carbon-, nitrogen-, and
sulfur-bearing phases down to submicron spatial scales, in order to
document processes that could sustain habitable environments on Mars,
both today and in the past.Assess the evidence for pre-biotic processes,
past life, and/or extant life on Mars by characterizing the signatures
of these phenomena in the form of structure/morphology, biominerals,
organic molecular and isotopic compositions, and other evidence within
their geologic contexts.Interpret the conditions of Martian water-rock
interactions through the study of their mineral products.Constrain the
absolute ages of major Martian crustal geologic processes, including
sedimentation, diagenesis, volcanism/plutonism, regolith formation,
hydrothermal alteration, weathering, and cratering. Understand
paleoenvironments and the history of near-surface water on Mars by
characterizing the clastic and chemical components, depositional
processes, and post-depositional histories of sedimentary
sequences.Constrain the mechanism and timing of planetary accretion,
differentiation, and the subsequent evolution of the Martian crust,
mantle, and core.Determine how the Martian regolith was formed and
modified, and how and why it differs from place to place.Characterize
the risks to future human explorers in the areas of biohazards, material
toxicity, and dust/granular materials, and contribute to the assessment
of potential in-situ resources to aid in establishing a human presence
on Mars.For the present-day Martian surface and accessible shallow
subsurface environments, determine the preservation potential for the
chemical signatures of extant life and pre-biotic chemistry by
evaluating the state of oxidation as a function of depth, permeability,
and other factors.Interpret the initial composition of the Martian
atmosphere, the rates and processes of atmospheric loss/gain over
geologic time, and the rates and processes of atmospheric exchange with
surface condensed species.For Martian climate-modulated polar deposits,
determine their age, geochemistry, conditions of formation, and
evolution through the detailed examination of the composition of water,
CO~2~, and dust constituents, isotopic ratios, and detailed stratigraphy
of the upper layers of the surface.MSR would have its greatest value if
rock samples are collected as sample suites that represent the diversity
of the products of various planetary processes. ***Sedimentary
materials*** likely contain complex mixtures of chemical precipitates,
volcaniclastics, impact glass, igneous rock fragments, and
phyllosilicates. Sediment samples are required to achieve definitive
measurements of life detection, observations of critical mineralogy and
geochemical patterns and occluded trace gases at submicron scales. On
Earth, ***hydrothermally altered rocks*** provide water, nutrients and
chemical energy necessary to sustain microorganisms, and could preserve
fossils in their mineral deposits. Hydrothermal processes substantially
affect mineralogy and volatile composition of the crust and atmosphere.
Chemical alteration occurring at near-surface ambient conditions
(typically \< \~20°C) create ***low temperature altered rocks*** that
include, among other things, aqueous weathering, palagonitization and
various oxidation reactions. Understanding the conditions under which
alteration proceeds at low temperatures would provide important insight
into the near-surface hydrological cycle, including fluid/rock ratios,
fluid compositions (chemical and isotopic, as well as redox conditions),
and mass fluxes of volatile compounds. ***Igneous rocks*** are expected
to be primarily lavas and shallow intrusive rocks of basaltic
composition. They are critical for investigations of the geologic
evolution of the Martian surface and interior because their geochemical
and isotopic compositions constrain both the composition of mantle
sources and the processes that affected magmas during generation,
ascent, and emplacement. ***Regolith*** samples record interactions
between crust and atmosphere, the nature of rock fragments, dust and
sand particles that have been moved over the surface, H~2~O and CO~2~
migration between ice and atmosphere, and processes involving fluids and
sublimation. Regolith studies would help facilitate future human
exploration by assessing toxicity and potential resources. ***Polar
ices*** would constrain present and past climatic conditions and help
elucidate water cycling. Surface ice samples from the Polar Layered
Deposits or seasonal frost deposits would help to constrain
surface/atmosphere interactions. Short cores could help to resolve
climate variability in the last few 10^5^ to 10^6^ years. ***Atmospheric
gas*** samples would constrain the composition of the atmosphere and
processes that influenced its origin and evolution. Trace organic gases
(e.g., methane and ethane) could be analyzed for abundances,
distribution, and relationships to a potential Martian biosphere.
Samples of Ne, Kr, CO~2~, CH~4~ and C~2~H~6~ would confer major
scientific benefits. Chemical and mineralogical analyses of Martian
***dust*** would help to elucidate the weathering and alteration history
of Mars. Given the global homogeneity of Martian dust, a single sample
is likely to be representative of the planet. A ***depth-resolved
suite*** of samples should be obtained from depths of cm to several m
within regolith or from rock outcrop in order to investigate trends in
the abundance of oxidants (e.g., OH, HO~2~, H~2~O~2~ and peroxy
radicals) and the preservation of organic matter. ***Other sample
suites*** include [*r*ock breccias]{.underline} that might sample rock
types that are otherwise not available, [tephra]{.underline} consisting
of fine-grained regolith material or layers and beds possibly delivered
from beyond the landing site, and [meteorites]{.underline} whose
alteration history could be determined and thereby provide insights into
Martian climatic history.

The following factors are key for achieving MSR science objectives.

1\. *Sample size.* A full program of science investigations would likely
require samples of ≥8 g for both rock and regolith. To support required
biohazard testing, each sample requires an additional 2 g, leading to an
optimal size of 10 g. Textural studies of some rock types might require
one or more larger samples of \~20 g. Material should remain to be
archived for future investigations.

2\. *Sample encapsulation.* To preserve scientific usefulness, returned
samples must not commingle, each sample must be linked uniquely to its
documented field context, and rock samples should remain mechanically
intact. A smaller number or mass of carefully managed samples would be
far more valuable than larger number or mass of poorly managed samples.
The encapsulation for at least some of the samples must be airtight to
retain volatile components.

3\. *Number of samples.* Studies of heterogeneities between samples
could provide as much or more information about processes as detailed
studies of a single sample. The minimum number of samples needed to
address the scientific objectives of MSR is 26 (20 rock, 3 regolith, 1
dust, 2 gas), in the case of recovery of the MSL cache. These samples
are expected to have a mass of about 350 g, and with sample packaging,
the total returned mass is expected to be about 650 g.

4\. *Sample acquisition system.* This system must [sample]{.underline}
both weathered exteriors and unweathered interiors of rocks,
[sample]{.underline} continuous stratigraphic sequences of outcrops that
might vary in their hardness, [relate]{.underline} the orientation of
sample structures and textures to those in outcrop surfaces, bedding
planes, stratigraphic sequences, and regional-scale structures, and
[maintain]{.underline} the structural integrity of samples. A mini-corer
and a scoop are the most important collection tools. A gas compressor
and a drill have lower priority but are needed for specific kinds of
samples.

5\. *Degree of selectivity of samples and documentation of field
context.* The scientific value of MSR depends critically upon the
ability to select wisely the relatively few returned samples from the
vast array of materials it would encounter. MSR objectives require at
least three kinds of *in situ* observations (color imaging, microscopic
imaging, and mineralogy measurement), and possibly as many as five (also
elemental analysis and reduced carbon analysis). No significant
difference exists in the observations needed for sample selection
[vs.]{.underline} sample documentation. Revisiting a previously occupied
site [might]{.underline} result in a reduction in the number of
instruments.

6\. *Sample temperature.* Some key species are sensitive to temperatures
exceeding those attained at the surface. Examples include organic
material, sulfates, chlorides, clays, ice, and liquid water. MSR's
objectives could most confidently be met if the samples are kept below
-20^o^C, and with less confidence if they are kept below +20^o^C.
Significant damage, particularly to biological studies, would occur if
the samples reach +50^o^C for 3 hours. Temperature monitoring during
return would allow any changes to be evaluated.

7\. *Diversity of the returned collection.* The diversity of the suites
of returned samples must be commensurate with the diversity of rocks and
regolith encountered. This guideline should substantially influence
landing site selection and rover operation protocols. It is
scientifically acceptable for MSR to visit only a single landing site,
but returning samples from two independent landing sites would be much
more valuable.

8\. *Surface operations.* In order to collect the suites of rocks
required by the MSR objectives, the lander must have significant surface
mobility, the capability to assess the diversity of surface materials,
and the ability to select samples that span that diversity. Depending on
the geology of the landing site, it is expected that a minimum of 6-12
months of surface operation would be required in order to reconnoiter a
site and identify, characterize and collect a set of samples.

9\. *Effects of the MSL/ExoMars caches upon MSR planning.* The decision
to direct the MSR mission to retrieve the MSL or ExoMars cache
conceivably might alter other aspects of the MSR mission. However, given
the limitations of the MSL cache, differences in planetary protection
requirements for MSL and MSR, the possibility that the MSR rover might
not be able to retrieve the cache, and the potential for MSR to make its
own discoveries, the MSR landed spacecraft should have its own
capability to characterize and collect at least some of returned
samples.

10\. *Planetary protection.* A scientifically compelling first MSR
mission could be designed without the capability to access and sample a
special region, defined as a region within which terrestrial organisms
may propagate. Unless MSR could land pole-ward of 30° latitude, access
rough terrain, or achieve significant subsurface penetration (\>5 m),
MSR is unlikely to be able to use incremental special regions
capabilities. Planetary protection draft test protocols should be
updated to incorporate advances in biohazard analytical methods.
Statistical principles governing mass requirements for sub-sampling
returned samples for these analyses should be re-assessed.

# 

[]{#__RefHeading___Toc191123508 .anchor}INTRODUCTIONSince the dawn of
the modern era of Mars exploration, the return of Martian samples to
Earth has been recognized as an essential component of a cycle of
exploration that began with orbital reconnaissance and *in situ* surface
investigations (see, for example, the discussion of sample return in
three decades of reports by the National Research Council: NRC, 1978;
1990a, 1990b, 1994; 1996; 2001; 2007). Global reconnaissance and surface
observations have "followed the water" and revealed a geologically
diverse Martian crust that could have sustained near-surface habitable
environments in the distant past. Major questions about life, climate,
and geology remain, and many of these require answers that only
Earth-based state-of-the-art analyses of samples could provide. The
stems from the fact that flight instruments cannot match the
adaptability and micro-analytical capability of Earth-based laboratories
(Gooding et al., 1989). For example, analyses conducted at the submicron
scale were crucial for investigating the ALH84001 meteorite, and they
would be essential for interpreting the returned samples. Furthermore,
spacecraft instrumentation simply cannot perform certain critical
measurements, such as, precise radiometric age dating, sophisticated
stable isotopic analyses, and comprehensive life-detection experiments.
If returned samples yield unexpected findings, subsequent investigations
could be adapted accordingly. Moreover, potions of returned samples
could be archived for study by future generations of investigators using
ever more powerful instrumentation.

Some samples from Mars are available for research on Earth in the form
of the Martian meteorites. The Martian meteorites, while indeed
valuable, provide a limited view of Martian geologic processes. These
samples are all igneous in nature, and minimally altered and thus do not
record the history of low temperature water based processes. These
samples certainly do not represent the most promising habitable
environments (Gooding et al., 1989), and it is possible that the most
extensively water-altered materials might be too fragile to survive an
interplanetary journey. Most meteorites have young crystallization ages
less than 1.3 billion years indicating that they represent only the most
recent igneous activity on Mars (Borg and Drake, 2005). Their
geochemical characteristics suggest that they are closely related to one
another and are consequently not representative of all of the lithologic
and geochemical diversity that is likely to be present in igneous
Martian rock suite (Borg and Draper, 2003; Borg et al., 2003; Symes et
al., 2008). Because the meteorites arrived by natural processes, and
lack geologic context, it is extremely difficult to extrapolate the
results from geologic studies of these samples to rocks observed from
space or on the Martian surface by landed spacecraft. In contrast,
returned samples could be obtained from sites within a known geologic
context and be selected in order to achieve the goals and objectives of
the Mars exploration community. Nevertheless, sample return missions
must surmount key challenges such as, engineering complexity, cost, and
planetary protection concerns, before their enormous potential could be
recognized. This document is intended to define this critical step
forward toward realizing the enormous potential of Mars sample return.

On July 10, 2007, Dr. Alan Stern, Associate Administrator for the
Science Mission Directorate (SMD), described to the participants in the
7^th^ International Conference on Mars his vision of achieving Mars
Sample Return (MSR) no later than the 2020 launch opportunity. He
requested that the financial attributes, scientific
options/issues/concerns, and technology development planning/budgeting
details of this vision be analyzed over the next year. The Mars
Exploration Program Analysis Group (MEPAG) is contributing to this
effort by preparing this analysis of the science components of MSR and
its programmatic context. To this end, MEPAG chartered the Next Decade
MSR Science Analysis Group (ND-MSR-SAG) to complete four specific tasks:

\(1\) Analyze what critical Mars science could be accomplished in
conjunction with, and complementary to, a next decade MSR mission.

\(2\) Evaluate the science priorities associated with guiding the makeup
of the sample collection to be returned by MSR.

\(3\) Determine the dependencies of mobility and surface lifetime of MSR
on the scientific objectives, sample acquisition capability, diagnostic
instrument complement, and number and type of samples.

\(4\) Support MSR science planning as requested by the International
Mars Exploration Working Group (IMEWG) MSR study. The charter is
presented in Appendix I.

The return of any reasonable sample mass from Mars would significantly
increase our understanding of atmospheric, biologic, and geologic
processes occurring there, as well as permit evaluation of the hazards
to humans on the surface. This is largely independent of how the samples
are selected, collected, and packaged for return, and stems from the
fact that there are no analogous samples on Earth. Thus, a mission
architecture in which a limited number of surface samples are collected
in a minimum amount of geologic context has been recommended in the past
and has huge scientific merit (e.g., MacPherson et al., 2005). It is
also important to realize that a significantly greater scientific yield
would result from samples that are more carefully selected. Analytical
results from samples that are screened, placed in detailed geologic
context, collected from numerous locations and environments, and are
packaged and transported under conditions that more closely approximate
those encountered on the Martian surface, would dramatically clarify the
picture of Mars derived from the mission, as well as allow analytical
results to be more rigorously extrapolated to the planet as a whole. As
a consequence of these facts, this document outlines a sampling strategy
that is necessary to [maximize]{.underline} scientific yield. The
inability to complete all of the surface operations associated with this
sampling strategy by no means negates the usefulness of these samples.
Rather, it results in a proportional loss of science yield of the
mission. Thus, this study is expected to constitute input to a Mars
program architecture trade analysis between scientific yield and cost.

# 

[]{#__RefHeading___Toc191123509 .anchor}EVALUATION PROCESSPrior to
beginning this study, the ND-SAG was briefed on the conclusions of the
NASA Mars Sample Return Science Steering Group II (MacPherson et al.,
2005; Appendix III) and the NRC Committee on an Astrobiology Strategy
for the Exploration of Mars. These reports document the importance of
sample return in a complete strategy for the exploration of Mars, and
many of their conclusions are reiterated here. However, the current
analysis has benefited from discoveries made in the interval since these
reports were written, such as phyllosilicates, silica, and the
distribution and context of poly-hydrated sulfates on the surface of
Mars. It is expected that some of the conclusions of this report will be
further elucidated and/or strengthened as results from Phoenix, MSL, and
ExoMars become available. This may be particularly true of the results
from analyses of organic matter and ices.

Assumptions used in this study are:

\(1\) The sample return mission would begin in either 2018 or 2020.

\(2\) MSL will launch in 2009, and will prepare a rudimentary cache of
samples that would be recoverable by the MSR mission. ExoMars would
carry a similar cache.

\(3\) The functionality of sample acquisition associated with MSR would
be independent of MSL. This functionality may either be landed at the
same time as the sample return element of MSR, or it may be separated
into a precursor mission.

\(4\) The Mars Exploration Program would maintain a stable program
budget of about \$625M/year that grows at 2%/year.

In order to complete these tasks and to link strongly the report of the
ND-SAG to the MEPAG Goals document, the ND-SAG was divided into four
subteams corresponding to each of the four main MEPAG goals. The goals,
as outlined in the Goals document, are: determine if life ever arose on
Mars, understand the processes and history of climate on Mars, determine
the evolution of the surface and interior of Mars, and prepare for human
exploration. Each group examined the individual investigations outlined
in the MEPAG Goals Document and considered the following:

-   
-   
-   
-   
-   
-   
-   

Whether sample return would facilitate the investigation.The type, mass,
number, and diversity of samples that would be required to complete the
investigation.The physical condition of the samples (rock, pulverized
rock, etc.).The vulnerability of specific sample types to degradation
effects during sample collection, encapsulation, and transport, as well
as the impact of this degradation on individual investigations.The
measurements required at the time of sample collection in order to
select appropriate samples and place them in the necessary geologic
context.The mobility necessary to obtain required samples.The packaging
and handling priorities necessary to preserve the characteristics of
interest in the samples.The results of this analysis are presented in
detail in Appendix II. Below we summarize the consensus of the ND-SAG
that was derived from this analysis.

# 

## 

[]{#__RefHeading___Toc191123510 .anchor}SCIENTIFIC OBJECTIVES OF MSR
[]{#__RefHeading___Toc191123511 .anchor}History, Current Context of
MSR's scientific objectives The 2003/2005 Mars Sample Return mission
(which was cancelled in 2000, prior to launch) was the most recent
effort that formulated scientific objectives for MSR. The way this
mission chose to frame its scientific objectives are listed in Table 1.
Since 2000, there have been numerous scientific advances that have
greatly increased our understanding of the red planet. It is critical to
take these into consideration in setting the new scientific objectives
for MSR. In particular, it is important to incorporate actual or
anticipated results from the following:

[Recent and on-going flight missions]{.underline}

Since the last MSR analysis in 2000, the Mars Global Surveyor
(1999-2006), Mars Odyssey (2002-present), Mars Exploration Rovers
(2004-present), Mars Express (mapping from 2004-present), and the Mars
Reconnaissance Orbiter (mapping from 2006-present) have made important
discoveries. These investigations have greatly improved our
understanding of Mars and have resulted in progressive refinement of key
Martian scientific objectives, as documented by the evolution of the
MEPAG Goals Document (MEPAG, 2001; MEPAG, 2004; MEPAG, 2005; MEPAG,
2006).

[Future (but pre-MSR) flight missions]{.underline}

Two major missions to the Martian surface are scheduled during the next
six years - the Mars Science Laboratory (MSL; scheduled for launch in
2009), and ExoMars (scheduled for launch in 2013). Both missions will
analyze rock samples on the surface of Mars using in-situ methods. It is
therefore necessary to consider the scientific objectives of these
missions when planning the objectives of the first MSR mission, and to
build upon their expected accomplishments. The scientific objectives of
the MSL and ExoMars missions, as of 2007, are listed in Table 1.

[Meteorite studies]{.underline}

More than 35 Martian meteorites have been found in Antarctica and desert
environments by meteorite recovery programs, including private and
government-sponsored efforts. The number of recovered meteorites
continually increases. As a consequence, MSR science objectives and
sample selection strategy must respond to scientific advances derived
from meteorite studies and also strive to complement the existing
meteorite collections.

[]{#__RefHeading___Toc191123496 .anchor}Table 1: Scientific Objectives,
'03/'05 MSR, 2009 MSL, and 2013 ExoMars (order listed as in the
originals)

![](media/image1.pct)*Sources of information: MSR: O'Neil and Cazaux
(2000); MSL: http://mepag.jpl.nasa.gov/MSL_Science_Objectives.html (as
of Jan. 7, 2008); ExoMars: Vago and Kiminek (2007)*

## 

[]{#__RefHeading___Toc191123512 .anchor}Possible Scientific Objectives
for a Next Decade MSR To translate the general statements about the
possible value of MSR into specifics, in Appendix II, the ND-SAG
analyzed how returned samples might contribute to each of the scientific
objectives and investigations described by MEPAG (2006). The
investigations listed in MEPAG (2006) do not have equal scientific
priority, nor do they benefit equally from returned sample analyses. By
considering the most important potential uses of returned samples, the
ND-SAG has formulated eleven relatively high-level scientific objectives
for MSR. However, we note that no single landing site could address all
of these objectives. Those objectives that any single MSR mission could
achieve would reflect the capabilities of its architecture/hardware and
the geologic terrain and local climate of the site. Even though all of
these objectives could not be achieved on the first MSR mission, it is
ND-SAG's hope that by making this analysis as complete as possible, it
will set the scene for future MSR missions beyond the first one.

[Prioritization of the Science Objectives]{.underline}

The ND-SAG team considered the relative priority of the possible
objectives listed below, using the following prioritization criteria:

1)  
2)  

The investigation priority in the Goals Document (MEPAG, 2006). The
analysis in Appendix II finds that returned samples could significantly
advance 34 of the investigations identified by MEPAG (2006), and each of
these investigations has been assigned a priority by MEPAG. The way in
which these 34 investigations are consolidated into the 11 objective
statements below is shown graphically in Appendix IV. The impact of MSR
on investigation(s) associated with these objectives. For thirteen of
the 34 investigations, MSR would not only be expected to advance them
more substantially than for the others, in some cases MSR is essential
(shown by the color coding in Appendix IV).However, the achievable
degree of progress towards these scientific questions would also depend
on the choice of landing site (and the kinds of samples that are
available to be collected there), the capability of the engineering
system (e.g. number and quality of samples), the degree of complexity of
the geologic process under study (and how many samples it might take to
evaluate it), and other factors. For example, Objective #5 involves
processes that are very complex, and a quantum jump in our understanding
may be difficult with only a few samples. However, the objective is
clearly important, and we should let it help guide the engineering. For
these reasons, the ND-SAG team felt it appropriate to list the
scientific objectives below in only two general priority groups: the
first five are considered high priority, and the last six are considered
medium priority. These priorities will clearly need to be reconsidered
as the specifics of MSR are refined.

1.  Determine the chemical, mineralogical, and isotopic composition of
    the crustal reservoirs of carbon, nitrogen, sulfur, and other
    elements with which they have interacted, and characterize carbon-,
    nitrogen-, and sulfur-bearing phases down to submicron spatial
    scales, in order to document processes that could sustain habitable
    environments on Mars, both today and in the
    past.[Discussion]{.underline}. A critical assessment of the
    habitability of past and present Martian environments must determine
    how the elemental building blocks of life have interacted with
    crustal and atmospheric processes (Des Marais et al., 2003). On
    Earth, such interactions have determined the bioavailability of
    these elements, the potential sources of biochemical energy, and the
    chemistry of aqueous environments (e.g., Konhauser, 2007).
    Earth-based investigations of Martian meteoritic minerals, textures
    and chemical composition at the sub-micron scale have yielded
    discoveries of their igneous volatiles, impact-related alteration,
    carbonates, organic carbon, atmospheric composition and the
    processes that shaped them. The search for extant live requires
    exploration of special regions (sites where life might be able to
    propagate) and thereby invokes stringent planetary protection
    protocols. These protocols are less stringent at sites other than
    special regions where the search for past life would target fossil
    biosignatures preserved in rocks. This objective is an extension of
    MSL Objectives 1 through 4 (Table 1), ExoMars Objectives 2 and 4
    (Table 1), and MEPAG Objective I-A, which collectively address the
    habitability potential of Martian environments.

2.  Assess the evidence for pre-biotic processes, past life, and/or
    extant life on Mars by characterizing the signatures of these
    phenomena in the form of structure/morphology, biominerals, organic
    molecular and isotopic compositions, and other evidence within their
    geologic contexts.[Discussion]{.underline}. The MER mission
    demonstrated that habitable environments existed on Mars in the past
    and that their geologic deposits are accessible at the surface
    (Squyres and Knoll, 2005; Des Marais et al., 2007). The Mars Express
    Orbiter OMEGA IR spectrometer mapped aqueous minerals that formed
    during the Noachian (Bibring et al., 2005; Poulet et al., 2005). The
    upcoming MSL and ExoMars missions will be able to provide
    information about the habitability (past or present) of their
    specific landing sites at even greater detail. Although ExoMars is
    designed to search for traces of past and present life (it should
    also be able to detect prebiotic organic materials), experience with
    Martian meteorites and, more especially, microfossil-containing
    rocks from the early Earth, has shown that identifying traces of
    life reliably is extraordinarily difficult because: (1) microfossils
    are often very small in size and (2) the quantities of organic
    carbon in the rocks that are identifiable as biogenic or abiogenic
    are often very low (Westall and Southam, 2006). The reliable
    identification of mineral and chemical biosignatures typically
    requires some particular combination of sophisticated
    high-resolution analytical microscopes, mass spectrometers and other
    advanced instrumentation. The particular combination of instruments
    that are most appropriate and effective for a given sample is often
    determined by the initial analyses. Accordingly, sample measurements
    must be conducted on Earth because they require adaptability in the
    selection of advanced instrumentation. . Note that the specifics of
    how this objective is pursued will be highly dependent on landing
    site selection. The search for extant life will require that the
    rover meet planetary protection requirements for visiting a "special
    region." The localities that are judged to be most prospective for
    evaluating prebiotic chemistry and fossil life might not be the most
    favorable for extant life. However, all returned samples will
    assuredly be evaluated for evidence of extant life, in part to
    fulfill planetary protection requirements, whether or not the
    samples were targeted for this purpose. This objective is an
    extension of MSL Objective 6 (Table 1), ExoMars Objective 1 (Table
    1), and MEPAG Objectives I-A, I-B and I-C, which address
    habitability, pre-biotic chemistry and biosignatures.

3.  Interpret the conditions of Martian water-rock interactions through
    the study of their mineral products.[Discussion]{.underline}. Both
    igneous and sedimentary rocks are susceptible to a broad range of
    water-rock interactions ranging from low-temperature weathering
    through hydrothermal interactions. These processes could operate
    from the surface to great depths within the Martian crust. Rocks and
    minerals affected by such processes are significant repositories of
    volatile light elements in the Martian crust, and they have also
    recorded evidence of climate and crustal processes, both past and
    present. The compositions and textures of rock and mineral
    assemblages frequently reveal the water to rock rations, fluid
    compositions and environmental conditions that created those
    assemblages (also discussed by MacPherson et al., 2001). A
    significant fraction of the key diagnostic information exists as
    rock textures, crystals and compositional heterogeneities at
    sub-micrometer to nanometer spatial scales. Textural relationships
    between mineral phases could help to determine the order of
    processes that have affected the rocks. This is key to determine,
    for example, whether a rock is of primary aqueous origin or
    alternatively was affected by water at some later time in its
    history. Accordingly, state-of-the art Earth-based laboratories are
    required to read the record of water-rock interactions and infer
    their significance for the geologic and climate history of Mars.
    This objective is an extension of the discoveries of MRO, MEX, and
    MER that there is an extensive history of ancient interaction
    between water and the Martian crust. Understanding these
    interactions over a broad range of spatial scales is critical for
    interpreting the hydrologic record and records of thermal and
    chemical environments. This objective is an extension of MSL
    Objectives 1, 2 and 8 (Table 1), ExoMars Objectives 2 and 4 (Table
    1), and MEPAG Objectives I-A, II-A, III-A and IV-A.

4.  Constrain the absolute ages of major Martian crustal geologic
    processes, including sedimentation, diagenesis, volcanism/plutonism,
    regolith formation, hydrothermal alteration, weathering, and
    cratering. [Discussion]{.underline}. Constraining the absolute ages
    of Martian rock-forming processes is an essential part of
    understanding Mars as a system. There are two aspects to this
    objective. First, dating individual flow units with known crater
    densities would provide a calibration of Martian cratering rates.
    This is critical for the interpretation of orbital data because
    crater chronology is the primary method for interpreting both
    relative and absolute ages of geologic units from orbit, and the
    method can be applied on a planetary scale. The scientific community
    has strongly advocated for the calibration of the crater chronology
    method since the inception of the Mars exploration program (MEPAG
    Investigation III-A-3). Second, we need to understand the timing of
    different geologic processes in the past as the planet has evolved
    in time and space. The suitability of the products of different
    geologic processes to the methods of radiometric geochronology
    depends on when the isotopic systems closed. Igneous rocks are by
    far the most useful (see summary in Borg and Drake, 2005).
    Constraints on low temperature processes, such as sedimentation,
    weathering, and diagenesis could be obtained most easily and
    definitively by finding sites that show discernable field
    relationships with datable igneous materials. For example, by
    determining the ages of igneous rocks that are interbedded with
    sedimentary rocks, the interval of time when the sediments were
    deposited could be constrained. In addition, the ages of secondary
    alteration of Martian meteorites have been measured with some
    success (Borg et al., 1999; Shih et al., 1998; 2002; Swindle et al.,
    2000). Accordingly, chemical precipitates formed during diagenesis,
    hydrothermal activity, and weathering may be datable using Ar-Ar,
    Rb-Sr and Sm-Nd chronometers. However, sophisticated Earth-based
    laboratories are required to perform these difficult measurements
    precisely, with multiple chronometers to provide an internal
    cross-check, and to reliably interpret the meanings of these ages.
    This objective is an extension of MSL Objective 1 (Table 1), ExoMars
    Objective 4 (Table 1), and MEPAG Objectives I-A, II-B, III-A and
    III-B, and has long been considered a major objective of MSR (e.g.
    McPherson et al., 2001; 2002).

5.  Understand paleoenvironments and the history of near-surface water
    on Mars by characterizing the clastic and chemical components,
    depositional processes, and post-depositional histories of
    sedimentary sequences.[Discussion]{.underline}. Experience with the
    Mars Exploration Rovers Spirit and Opportunity demonstrates that
    sedimentary rock sequences, which include a broad range of clastic
    and chemical constituents, are exposed and that sedimentary
    structures and bedding are preserved on the Martian surface.
    Discoveries by MRO and Mars Express further demonstrate the great
    extent and geological diversity of such deposits. Sedimentary rocks
    could retain high-resolution records of a planet's geologic history
    and they could also preserve fossil biosignatures. As such,
    sedimentary sequences are among the targets being considered by MSL
    and ExoMars. Previous missions have also demonstrated that the
    sedimentologic and stratigraphic character of these sequences could
    be evaluated with great fidelity, comparable to that attained by
    similar studies on Earth (e.g., Squyres and Knoll, 2005; Squyres et
    al., 2007). The physical, chemical and isotopic characteristics of
    such sequences would reveal the diversity of environmental
    conditions of the Martian surface and subsurface before, during and
    after deposition. But much of the key diagnostic information in
    these sequences occurs as textures, minerals and patterns of
    chemical composition at the submicron scale. Future robotic missions
    might include microscopic imaging spectrometers to examine these
    features. However, definitive observations of such features probably
    will also require thin section petrography, SEM, TEM, and other
    sophisticated instrumentation available only in state-of-the-art
    Earth-based laboratories. This objective is an extension of MSL
    Objectives 1, 2 and 8 (Table 1), ExoMars Objectives 2 and 4 (Table
    1), and MEPAG Objectives I-A, II-A, III-A and IV-A .

6.  Constrain the mechanism and timing of planetary accretion,
    differentiation, and the subsequent evolution of the Martian crust,
    mantle, and core.[Discussion]{.underline}. Studies of Martian
    meteorites have provided a fascinating glimpse into the fundamental
    processes and timescales of accretion (e.g., Wadhwa, 2001; Borg et
    al., 2003; Symes et al., 2008; Shearer et al., 2008) and subsequent
    evolution of the crust, mantle, and core (e.g. Treiman, 1990;
    Shearer et al., 2008). Martian meteorites also record a history of
    fluid alteration as shown by the presence of microscopic clay and
    carbonate phases (e.g. Gooding et al. 1991, McKay et al. 1996,
    Bridges et al. 2001). Although the trace element and isotopic
    variability of the Martian meteorite suite far exceeds that observed
    in equivalent suites of basalts from Earth and Moon (Borg et
    al., 2003) the apparent diversity of igneous rocks identified by
    both orbital and surface missions far exceeds that of the meteorite
    collection. This implies that an extensive record of the
    differentiation and evolution of Mars has been preserved in igneous
    lithologies that have not been sampled. Samples returned from
    well-documented Martian terrains would provide a broader planetary
    context for the previous studies of Martian meteorites and also lead
    to significant insights into fundamental crustal processes beyond
    those revealed by the Martian meteorites. Key questions include the
    following: (1) When did the core, mantle, and crust first form? (2)
    What are the compositions of the Martian core, mantle, and
    crust? (3) What additional processes have modified the crust,
    mantle, and core and how have these reservoirs interacted through
    time? (4) What processes produced the most recent crust? (5) What is
    the evolutionary history of the Martian core and magnetic field? (6)
    How compositionally diverse are mantle reservoirs? (6) What are the
    thermal histories of the Martian crust and mantle and how have they
    constrained convective processes? (7) What is the nature of
    fluid-based alteration processes in the Martian crust? Coordinated
    studies of Martian meteorites and selected Martian samples involving
    detailed isotopic measurements in multiple isotopic systems, the
    study of microscopic textural features (melt inclusions, shock
    effects), and comparative petrology and geochemistry are needed to
    answer these questions definitively. These data will provide the
    basis for model ages of differentiation that are placed in the
    context of solar system evolution. They will also permit some of the
    compositional characteristics of crust, mantle, and core to be
    determined, which in turn will allow geologic interactions between
    these reservoirs to be evaluated, as well as their thermal histories
    to be elucidated. The tremendous value of this approach has been
    validated by geochemical studies on the returned lunar samples that
    have been more informative than any other means in deciphering the
    geologic history of the Moon. This objective is an extension of MSL
    Objective #1 (Table 1), ExoMars Objective #4 (Table 1), and MEPAG
    Objectives I-A, II-A, III-A and III-B and has long been considered a
    major objective of MSR (e.g. McPherson et al., 2001; 2002).

7.  Determine how the Martian regolith was formed and modified, and how
    and why it differs from place to place.[Discussion]{.underline}. The
    Martian regolith preserves a record of crustal, atmospheric and
    fluid processes. Regolith investigations would determine and
    characterize the important ongoing processes that have shaped the
    Martian crust and surface environment during its history. It is a
    combination of broken/disaggregated crustal rocks, impact-generated
    components (Schultz and Mustard, 2004), volcanic ash (Wilson and
    Head, 2007), oxidized compounds,, ice , aeolian deposits and
    meteorites. The Viking, Pathfinder and MER landers have also
    revealed diverse mineral assemblages within regolith that include
    hematite nodules, salt-rich duricrusts, and silica-rich deposits
    (e.g. Ruff et al. 2007; Wanke et al. 2001) that show local
    fluid-based alteration. The regolith contains fragments of local
    bedrock as well as debris that were transported regionally or even
    globally. These materials would accordingly provide local, regional
    and global contexts for geological and geochemical studies of the
    returned samples. Martian surface materials have also recorded their
    exposure to cosmic ray particles. Cosmic ray exposure ages obtained
    at Apollo landing sites have helped to date lunar impact craters
    (e.g. Eugster, 2003). Regolith returned from Mars should provide
    similar information that could in turn be used to constrain the
    absolute ages of local Martian terrains. An MSR objective would be
    to examine returned samples of regolith mineral assemblages in order
    to determine the abundances and movement of volatile-forming
    elements and any organic compounds in near-surface environments and
    to determine their crustal inventories. The abundance of ice in the
    regolith varies dramatically across the Martian surface. At high
    latitudes water ice attains abundances of tens of weight-percent
    below the top few tens of cm. Inventories of water ice at near
    equatorial latitudes are less understood but ice might occur below
    the top few cm (Feldman et al. 2004). The regolith is assumed to
    harbor large fraction of the Martian CO~2~ and H~2~O inventories but
    their abundance has not yet been accurately determined. This
    objective is an extension of MSL Objectives 1, 2, 3, 4, 6, 7, 8
    (Table 1), ExoMars Objectives 1, 2 and 3 (Table 1), and MEPAG
    Objectives I-A, I-B, I-C, II-B, III-A and IV-A.

8.  Characterize the risks to future human explorers in the areas of
    biohazards, material toxicity, and dust/granular materials, and
    contribute to the assessment of potential in-situ resources to aid
    in establishing a human presence on Mars.[Discussion]{.underline}.
    Returned samples could help to accomplish four tasks that are
    required to prepare for human exploration of Mars (see Appendix II).
    These tasks include: 1). Understanding the risks that granular
    materials at the Martian surface present to the landed hardware
    (Investigation IVA-1A), 2) Determining the risk associated with
    replicating biohazards (i.e., biological agents, Investigation
    IVA-1C), 3) Evaluating possible toxic effects of Martian dust on
    humans (Investigation IVA-2), and 4) Expanding knowledge of
    potential in-situ resources (Investigation IVA-1D). The human
    exploration community has consistently advocated that these tasks
    are essential for understanding the hazards and to plan the eventual
    human exploration of Mars at an acceptable level of risk (Davis,
    1998; NRC, 2002; Jones et al., 2004). Regarding possible Martian
    biohazards, analyses of robotically returned Martian samples might
    be required before human missions could commence, in order to
    quantify their medical basis and to address concerns related to
    planetary protection from both a forward and back contamination
    perspective (Warmflash et al, 2007). This objective is an extension
    of MSL Objective 7 (Table 1), ExoMars Objective #3 (Table 1), and
    MEPAG Objective IV-A.

9.  For the present-day Martian surface and accessible shallow
    subsurface environments, determine the preservation potential for
    the chemical signatures of extant life and pre-biotic chemistry by
    evaluating the state of oxidation as a function of depth,
    permeability, and other factors.[Discussion]{.underline}. 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 and within weathered rocks is
    critical investigating in greater detail the nature and abundance of
    any organic carbon on the surface of Mars. Understanding the
    oxidation chemistry and the processes controlling its variations
    would aid in predicting subsurface habitability if no organics are
    found on the surface, and also in understanding how such oxidants
    might participate in redox reactions that could provide energy for
    life. Potential measurements include identifying species and
    concentrations of oxidants, characterizing the processes forming and
    destroying them, and characterizing concentrations and fluxes of
    redox-sensitive gases in the lower atmosphere. Measuring the redox
    states of natural materials is difficult and may require returned
    samples. This objective is an extension of MSL Objective 1, and 8
    (Table 1), ExoMars Objective #2 (Table 1), and MEPAG Objectives I-A,
    III-A and IV-A.

10. Interpret the initial composition of the Martian atmosphere, the
    rates and processes of atmospheric loss/gain over geologic time, and
    the rates and processes of atmospheric exchange with surface
    condensed species.[Discussion]{.underline}. The modern chemistry of
    the Martian atmosphere reflects the integration of three major
    processes, each of which is of major importance to understanding
    Mars: 1). The initial formation of the atmosphere, 2). The various
    processes that have resulted in additions or losses to the
    atmosphere over geologic time, and 3). The processes by which the
    atmosphere exchanges with various condensed phases in the upper
    crust (e.g., ice, hydrates and carbonates). Many different factors
    have affected the chemistry of the Martian atmosphere, however if
    the abundance and isotopic composition of its many chemical
    components could be measured with sufficient precision, definitive
    interpretations are possible. We have already gathered some
    information about Martian volatiles from isotopic measurements by
    Viking and on Martian meteorites (Owen et al., 1977; Bogard et al.,
    2001). In addition, MSL will have the capability to measure some,
    but not all, of the gas species of interest with good precision.
    This leaves two planning scenarios: If for some reason MSL does not
    deliver its expected data on gas chemistry, this scientific
    objective would become quite important for MSR. However, even if MSL
    is perfectly successful, it will not be able to measure all of the
    gas species of interest at the precision needed, so returning an
    atmosphere sample could still be an important scientific objective
    for MSR. This objective is an extension of MSL Objective 5 (Table 1)
    and MEPAG Objectives I-A, II-A, II-B, and III-A.

11. For Martian climate-modulated polar deposits, determine their age,
    geochemistry, conditions of formation, and evolution through the
    detailed examination of the composition of water, CO~2~, and dust
    constituents, isotopic ratios, and detailed stratigraphy of
    the upper layers of the surface.[Discussion]{.underline}. The polar
    layered deposits represent a detailed record of recent Martian
    climate history. The composition of the topmost few meters of ice
    reflect the influence of meteorology, depositional episodes, and
    planetary orbital/axial modulation over the timescales of order
    10^5^ to 10^6^ years (Milkovich and Head, 2005). This objective
    addresses the priorities of MEPAG Investigation IIB-5. Terrestrial
    ice cores have contributed fundamentally to interpreting Earth's
    climate history. Similar measurements of Martian ices could be
    expected to reveal critical information about that planet's climate
    history and its surface/atmosphere interactions (Petit et al., 1999;
    Hecht et al., 2006). The ability of ice to preserve organic
    compounds (and, potentially, organic biosignatures) may help address
    objectives associated with habitability and pre-biotic chemistry and
    life (MEPAG Goal 1; Christner et al., 2001). By exploring lateral
    and vertical stratigraphy of active ice layers and facilitating
    state-of-the-art analyses of returned materials, a rover-equipped
    sample return mission would significantly improve our understanding
    beyond what the Phoenix stationary lander is expected to achieve at
    its single high-latitude site. This objective is an extension of
    MEPAG Objectives I-A, II-A, II-B, and III-A.

# 

[]{#__RefHeading___Toc191123513 .anchor}SAMPLES REQUIRED TO ACHIEVE THE
SCIENTIFIC OBJECTIVESThe MSR science objectives imply the return of
several types of Martian samples. These types arise from the variety of
significant processes (e g., igneous, sedimentary, hydrothermal, aqueous
alteration, etc.) that played key roles in the formation of the Martian
crust and atmosphere. Each process creates varieties of materials that
differ in their composition, location, etc. and that collectively could
be used to interpret that process. Accordingly we define a "sample
suite" as the set of samples required to determine the key process(es)
that formed them. On Earth, suites typically consist of a few to
hundreds of samples, depending on the nature, scale, and detail of the
process(es) being addressed. However, as discussed in a subsequent
section, suites of about 5 to 8 samples are thought to represent a
reasonable compromise between scientific needs and mission constraints.
The characteristics of each type of sample suite are presented below.

## 

[]{#__RefHeading___Toc191123514 .anchor}Sedimentary materials rock
suite. Sedimentary materials would be a primary sampling objective for
MSR. Data from surface-roving and orbiting instruments indicate that
lithified and unlithified sedimentary materials on Mars likely contain a
complex mixture of chemical precipitates, volcaniclastic materials and
impact glass, igneous rock fragments, and phyllosilicates (McLennan and
Grotzinger, in press). Chemical precipitates detected or expected in
Martian materials include sulfates, chlorides, silica, iron oxides, and,
possibly, carbonates and borates (McLennan and Grotzinger, in press).
Sand- to silt-sized igneous rock fragments are likely to be the dominant
type of siliciclastic sediment on Mars. Sediments rich in
phyllosilicates are inferred to derive from basaltic to andesitic
igneous rocks that have undergone weathering leading to the formation of
clay minerals and oxides (Poulet et al., 2005; Clark et al., 2007).
Products of weathering are moved by transporting agents such as wind,
gravity, and water to sites of deposition and accumulation. Sedimentary
materials accumulate by addition of new material on the top of the
sediment column, thereby permitting historical reconstruction of
conditions and events starting from the oldest at the bottom and
continuing to the youngest at the top of a particular depositional
sequence. However pervasive impacts have "gardened" (stirred and
disrupted) many such layered sedimentary deposits, therefore undisturbed
sequences must be sought. Although hydrothermal deposits and *in situ*
low-temperature alteration products of igneous rocks are products of
sediment-forming processes, they are presented in separate sections in
order to emphasize their importance.

Chemical precipitates formed under aqueous conditions could be used to
constrain the role of water in Martian surface environment (e.g., Clark
et al., 2005; Tosca et al., 2005). Precipitates could form within the
water column and settle to the sediment surface or they could
crystallize directly on the sediment surface as a crust. Any
investigation that involves habitability, evidence of past or present
life, climate processes, or evolution of the Martian atmosphere would be
enabled by the acquisition of these rocks(Farmer and Des Marais, 1999).
Some, but not all, chemical precipitates have interlocking crystalline
textures with low permeability, potentially allowing preservation of
trapped labile constituents such as organic compounds and sulfides
(e.g., Hardie et al., 1985). Thus, intact samples of chemical
precipitates would be critical for unravelling the history of aqueous
processes, including those that have influenced the cycling of carbon
and sulfur.

Siliciclastic sedimentary materials are moved as solid particles and are
deposited when a transporting agent loses energy. Variation in grain
size and textural structures at scales from millimeters to meters are
important indicators of depositional processes and changing levels of
energy in the environment (Grotzinger et al., 2005). Secondary
mineralization of sedimentary materials is likely to be minimal if pores
spaces are filled with dry atmospheric gases but is likely to be
substantial if pore spaces are filled with fresh water or brine
(McLennan et al., 2005). Sub-mm textures at grain boundaries are
indicative of processes that have modified the sedimentary deposit..
Thus, individual samples of siliciclastic sedimentary materials would
provide insights into transporting agents, chemical reactions,
availability of water in surface environments, and the presence of
currents or waves. A series of samples through a sedimentary sequence
would provide critical insight into rates and magnitudes of sedimentary
processes. Certain deposits such as chemically precipitated sediments,
varved sediments, ice, etc. could provide insights into climatic cycles.
Siliciclastic sedimentary materials are central to investigations
involving past and present habitability and the evolution of the Martian
surface. Fine-grained siliciclastic materials rich in phyllosilicates
are likely to have low permeability, thus increasing the potential for
preservation of co-deposited organic matter and sulfide minerals (Potter
et al., 2005). Like chemical precipitates, samples of phyllosilicates
that were deposited in aqueous environments would be critical for
unravelling the carbon and sulfur cycle on Mars.

## 

[]{#__RefHeading___Toc191123515 .anchor}Hydrothermal rock suite
Hydrothermal deposits are relevant to the search for traces of life on
Mars for several reasons (Farmer, 1998). On Earth, such environments can
sustain high rates of biological productivity (Lutz et al., 1994). The
microbial life forms inhabiting these environments benefit from various
thermodynamically favorable redox reactions, such those involving hot
water and mineral surfaces. These conditions can also facilitate the
abiotic synthesis of organics from CO~2~ or carbonic acid (McCollom and
Shock, 1996). The kinds of molecules that are thus synthesized include
monomeric constituents used in the fabrication of cell membranes
(Eigenbrode, 2007). Not only do microorganisms inhabiting hydrothermal
systems have ready access to organics, they are also supplied with
abundant chemical energy provided by the geochemical disequilibrium due
to the mixing of hot hydrothermal fluids and cold water. These
energy-producing reactions are highly favorable for the kinds of
microorganisms that obtain their energy from redox reactions involving
hydrogen or minerals containing sulfur or iron (Baross and Deming, 1995

Another important aspect of the habitability of hydrothermal systems is
the ready availability of nutrients. High temperature aqueous reactions
leach volcanic rocks and release silica, Al, Ca, Fe, Cu, Mn, Zn and many
other trace elements that are essential for microorganisms. Because
hydrothermal fluids are rich in dissolved minerals, they create
conditions favorable for the preservation of biosignatures, i.e., traces
of the life forms that inhabit them. Although the organic components of
mineralized microfossils can be oxidized at higher temperatures
(\>100°C), more recalcitrant organic materials (e.g., cell envelopes and
sheaths) can be trapped and preserved in mineral matrices at lower
temperatures (\<35^o^C; Cady and Farmer, 1996; Farmer, 1999), thus
allowing chemical and isotopic analysis of organic biosignatures.
Minerals implicated in the fossilization of hydrothermal microorganisms
include silica, calcium carbonate and iron oxide.

Some of the earliest life forms on Earth might have inhabited
hydrothermal environments (Farmer, 2000). Hyperthermophiles occupy the
lowest branches of the tree of life (Woese et al., 1990). Indeed,
hydrothermal vent environments, with their organic molecule-forming
reactions, chemical disequilibria and high nutrient concentrations are
considered as a possible location for the origin of life (Russell and
Hall, 1996). However some would argue that the position of
hyperthermophiles at the base of the tree of life is an artifact caused
by the fact that such environments would have represented protected
habitats during the late heavy bombardment period when a large part of
the world ocean was probably volatilized (Sleep et al., 1989). But the
fact that hydrothermal environments could serve as protected habitats in
hostile conditions is relevant to the early history of Mars.

Recently, it has been suggested that the suites of minerals found at the
surface of Mars (including silica and sulfates) could be related to
hydrothermal/fumarolic activity (e. g. Bishop et al., 2002; Squyres et
al., 2007; Yen et al., 2007; Squyres et al., Science, submitted).
Hydrothermal activity is to be expected because volcanic activity has
occurred at the surface within the last couple of million years,
demonstrating that active heat sources still exist (Neukum et al.,
2004). Hypothesizing that life arose on Mars and flourished at the
surface during the first 500 My of its history, the gradual
deterioration in surface conditions would have confined life forms
beneath the surface, perhaps to be preserved in the cryosphere and
elsewhere. Conceivably, life might have adapted to subsurface
environments during the first 500 My and has persisted there since. The
subsurface environment might have sustained only very low rates of
productivity, but it is also the most stable environment and a potential
haven for life during large impacts. Volcanic activity in the vicinity
of the cryosphere would lead to active hydrothermal systems that, in
some cases, might extend to the surface (Clifford, 1987).

The detection of hydrothermal activity on Mars is extremely significant
since these environments could represent ideal habitats for
microorganisms that obtain their carbon and energy from inorganic
sources. They might host extant life as well as the fossilized traces of
its ancestors. Returning intact samples of this lithology might be
difficult for geologically recent material, which tends to be friable.
It would therefore be very important to document the geologic context of
such samples in case they do not survive the return trip whole.

Criteria for sample size, selection, and acquisition protocol would be
the same as for the sedimentary suite. Examples of possible lithologies
for the hydrothermal suite include samples from subsurface veins,
fumarole deposits, surface spring deposits from vent areas to distal
apron environments, as well as altered host rocks.

## 

[]{#__RefHeading___Toc191123516 .anchor}Low temperature altered rock
suite. Low temperature alteration processes occur at near ambient
conditions on the Martian surface (typically less than about 20°C) and
include, among other things, aqueous weathering (including, certain
forms of palagonitization) and a variety of oxidation processes.
Spectral observations made by Viking and Pathfinder first inspired the
notion that rock surfaces on Mars are coated with thin veneers of
altered material. Crude depth profiling provided by the RAT experiment
on the MER rovers revealed thin (mm-scale) alteration rinds on most rock
surfaces studied. The exact nature of the alteration processes remains
under discussion, but most investigators agree that low-temperature,
relatively acidic aqueous conditions were involved (e.g., Haskins et
al., 2005; Hurowitz et al., 2006; Ming et al., 2006).

Low temperature processes also influence the regolith during and after
its deposition. The sulfur-rich composition of regolith has long been
attributed to low temperature aqueous processes that yielded sulfate and
other secondary minerals. This was confirmed when the MER rovers
identified reactive magnesium and ferric sulfate minerals in the soils
(Yen et al., 2007). The Viking gas exchange and labelled release
experiments also demonstrated that a reactive and oxidizing compound in
the regolith was capable of breaking down many organic species. The
nature and origin of this compound remains controversial, but various
models call for low temperature processes, such as photochemical
alteration, impact crushing, or oxidizing acid interactions (Yen et al.,
2000; Hurowitz et al., 2007).

Understanding the conditions under which low temperature alteration
processes proceed would provide important insight into the near-surface
hydrological cycle, including fluid/rock ratios, fluid compositions
(chemical and isotopic, as well as redox conditions), and the mass
fluxes of volatile compounds (see also MacPherson et al., 2001, 2002).
It would be particularly important to analyze complete alteration
profiles, whether on rock surfaces or within regolith columns, because
they would also constrain the kinetics of these alteration reactions.

Representative, intact (or at least reconstructed) profiles on rock
surfaces would be required in order to understand these alteration
reactions. Recent experimental work has shown that parent rock
compositions (mineralogy) are an important variable in understanding
these processes (Tosca et al., 2004; Golden et al., 2005). Consequently,
a diverse compositional suite would be highly desirable and would
require sample site characterization during sample selection. Alteration
profiles on rock surfaces would most readily be acquired by coring. The
scales of alteration profiles range from less than one mm to perhaps as
much as one cm, and so sample sizes of at least 2 cm would be needed.
Because alteration profiles are likely to contain small amounts of
sulfate and perhaps other reactive minerals, these samples would be
susceptible to degradation during sampling and transport to Earth by
processes such as dehydration and chemical reaction, which in turn could
also affect their physical integrity. Accordingly, sample encapsulation
is deemed critical.

## 

[]{#__RefHeading___Toc191123517 .anchor}Igneous rock suite. The igneous
rocks on Mars are expected to be composed primarily of lavas and shallow
intrusive rocks of basaltic composition (McSween et al., 2003;
Christensen et al., 2005), along with volcanic ash deposits (e.g. Wilson
and Head, 2007). Although more and less evolved silicic and ultramafic
magmatic rocks may potentially be present and would be of great
interest, they have not yet been unambiguously identified on the
surface. Igneous rocks would be central to investigations that reveal
the geologic evolution of the Martian surface and interior because their
geochemical and isotopic compositions constrain both the composition of
mantle source regions as well as the processes that affected magmas
during their generation, ascent, and emplacement (see also MacPherson et
al., 2001; 2002). Although spacecraft instrumentation could measure many
major elements, Earth-based analyses of returned samples would be
necessary to determine most trace element and isotopic abundances of
rocks. Melting and crystallization experiments in terrestrial
laboratories would be based on the compositions of igneous rocks. Trace
siderophile element abundances and isotopic compositions in igneous
rocks could constrain the nature of the core and possibly its
interaction with the mantle. Because magmas carried dissolved volatiles
to the surface, these rocks would also be critical to understanding the
inventories of degassed volatiles and the cycling of water and carbon.

Only igneous rocks could be reliably dated using absolute radiometric
dating techniques, therefore they would be critical for calibrating the
Martian stratigraphic timescale. Quantifying cratering rates would allow
absolute ages of Martian surfaces to be derived from crater densities
(Hartmann and Neukum, 2001). Unaltered igneous rocks that are
geographically linked to extensive terranes with known crater densities
would be required. This linkage would likely be accomplished by
comparing their geochemical/mineralogical characteristics with local
bedrock and by characterizing regional units using orbital remote
sensing.

A large proportion of rocks on the Martian surface are likely to have
experienced at least some low-temperature alteration (Wyatt et al.,
2004). However significantly weathered samples would not satisfy the
needs of these investigations and instead would be better suited to
investigations involving rock/water interactions. Consequently, the
low-temperature alteration products associated with the weathering of
the igneous rock suite are discussed separately.

To accommodate these investigations, a suite of igneous samples with as
much chemical and textural diversity as possible would be required.
Although some basaltic rocks may appear similar in terms of major
element abundances and mineralogy, a suite collected over some
geographic area would be likely to exhibit differences in trace element
and isotopic compositions that would be highly informative. If different
types of igneous rocks are present, (e.g. ultramafic or silicic rocks),
additional samples of these rocks should be collected, as these could
constrain fractionation processes on Mars. It is important to note that
many different scientific objectives could be met with the same samples.
For example, radiometric dating of a lava flow that overlies a
sedimentary sequence might constrain the cratering rate, the mechanisms
and timing of planetary differentiation and evolution, and the period
when sedimentation occurred. The igneous rock suite is relatively
robust, therefore most geologic objectives could be met with minimal
temperature control and encapsulation procedures. However, interactions
with fluids derived from dehydration of other samples, physical mixing,
and the abrasion of rock chips during transport could all be detrimental
to these investigations.

## 

[]{#__RefHeading___Toc191123518 .anchor}RegolithThe Martian regolith
reflects interactions between the crust and the atmosphere, the nature
of rock fragments, dust and sand particles that have been moved over the
surface, H~2~O and CO~2~ migration between ice and the atmosphere, and
processes involving fluids and sublimation. Understanding regolith
chemistry and mineralogy is vital to determining the fates of any
organic constituents. Some aspects of regolith studies necessarily
overlap studies of the local rock petrology, geochemistry, and
hydrothermal and low- temperature alteration processes. Although
global-scale transport processes may have homogenized much of the
fine-grained Martian regolith components, as shown by the similarity of
most Viking and Pathfinder soil compositions (e.g. Carr, 2006), the MER
rovers have demonstrated that the regolith also contains a diverse range
of mineral assemblages, some of which originated locally. Other
materials, such as volcanic ash (Wilson and Head, 2007) and impact glass
(Mustard and Schultz, 2004), may have come from greater distances. 
Understanding the mechanisms by which these assemblages are produced is
necessary in order to understand the evolution of the Martian surface
and key fluid processes. The recent identification of a silica-rich
component in a Gusev crater soil deposit that perhaps formed though
hydrothermal processes (Ruff et al. 2007) and the presence of hematite
spherules in the Opportunity soil (Squyres et al. 2004) highlight the
importance of regolith studies. The mm-scale alteration rinds identified
on rocks in the regolith in Gusev might have resulted from the reaction
of S- and Cl-bearing species with minute amounts of liquid water
(Haskins et al., 2005). Studying the mineralogy of alteration rinds
within regolith granules would give an insight to water and oxidation
processes on Mars over long timescales (MacPherson et al. 2001).

The mixed and complex nature of regolith samples could lead to
unexpected findings. For example, Bandfield et al. (2003) proposed that
atmospheric dust on Mars contains a few percent carbonate. This is
important because carbonate provides a record of atmosphere-water-crust
interaction. However, carbonates have not yet been conclusively
identified on the surface of Mars, making the search for carbonates
within the dust from a regolith sample an important component for
detailed mineralogical study. Microscopic examination of the regolith
sample in terrestrial laboratories would enable micrometeorites to be
identified from which meteorite fluxes could be estimated.

A regolith sample is also likely to retain some CO~2~ and H~2~O. These
might occur as ice or mixed clathrates. If acquired samples could be
refrigerated at -10° to -20°C, it might be possible to identify their
various potential species. Determination of CO~2~ and H~2~O abundance
and isotopic compositions would lead to a greater understanding of the
global inventories and cycling between crust, atmosphere and poles of
these compounds. For example, accurate paleotemperatures of hydrothermal
systems could be determined from measurements of ^18^O/^16^O isotopic
fractionation during water-mineral isotopic exchange in hydrothermal
assemblages (sampled across Mars or in meteorites) using the isotopic
analyses of Martian ice as the starting water reservoir composition
(Bridges et al. 2001, Valley et al. 1997). If a polar landing is not
chosen then the regolith sample would take on additional importance as a
likely source of the ice.

It is important to note that for a geologic unit with a high presumed
degree of heterogeneity, like the Martian regolith, many of the
measurements of interest could (and should) be done in situ, and
regolith studies should be an important target for both landed missions
and MSR. The basic field relationships, including measuring physical
properties and their variation vertically and laterally, would best be
done in place. However, sample return would be the best way to identify
the altered and partially altered materials, trace minerals (e.g.,
carbonates), rare lithologies, etc. It is also important to note that
our experience with the Spirit rover has shown us that we don't really
have a good way of knowing the magnitude of geochemical/geologic
variability within this unit on a planetary scale, and how many samples
will be necessary to characterize it. This objective should be thought
of as one that would require more than just the first MSR mission.

## 

[]{#__RefHeading___Toc191123519 .anchor}Polar IceSamples of polar ice
would be necessary to constrain the present and past climatic
conditions, as well as elucidate cycling of water, on Mars. The samples
necessary to achieve these objectives could include discreet samples of
surface ice from the Polar Layered Deposits (PLD) or a seasonal frost
deposit. Short cores (\~1 cm diameter x 30 cm length) from the PLD or
subsurface ice deposit would also be desirable. A single sample could
provide critical input on surface/atmosphere interactions. A short core
might resolve climate variability in the last few 100 Ka to 1 Ma
\[Milkovich and Head, 2005\]. Annual layers could be observed in core
samples and isotopic signatures (δ^18^O, D/H) are expected to define
annual temperature variability, changes in water reservoir availability
and exchange with the atmosphere, and short-term climate variations
(Fisher, 2007). The composition of entrained non-ice dust materials
(e.g., aeolian, volcanic tephra, impact glass) would help determine the
sources and relative proportions of dust reaching the poles.  Changes in
the amount of entrained non-ice dust with depth would help to constrain
estimates of the modulation of large-scale dust events and their
seasonal variability (Herkenhoff et al., 2007). The desired sample
localities include both north and south residual ice deposits, both
north and south PLD, and both mid-latitude and tropical glacial deposits
(Head et al., 2006; Head and Marchant, 2003; Shean et al., 2005; Shean
et al., 2007). Ideally several core samples would be extracted over
lateral distances of \~1 km to validate stratigraphic models based on
orbital imagery. On the polar plateaus, the areas between scarps and
troughs are wide and flat, and the north polar troughs have walls whose
maximum slopes are \~10°. A traverse that acquires multiple discreet
samples along trough slopes where stratigraphy is well exposed would
afford extensive vertical sampling of climate history (Carsey et al.,
2005). Trough slopes are well within the range of slopes that the Mars
Exploration Rovers successfully traversed in Endurance and Victoria
craters and the Columbia Hills.

Either drilling or coring technologies would be required to sample the
ice. The capability to acquire 30 cm cores is not expected to require
significant technology development. Technologies for coring or small
drills exist from MSL and have been proposed for Scout missions.
Scooping or drilling would be required to sample surface ice or ice
buried under dry soil. These samples must be encapsulated and kept
frozen; however, melt water would still provide critical isotopic and
compositional information. Dividing cores into sub-samples is expected
to be similar to that for rock samples but it must be conducted under
controlled conditions. Stratigraphic analyses of the cores must be
conducted before they are divided and, if sub-samples are accurately
catalogued, the core could be returned to Earth in sections.

## 

[]{#__RefHeading___Toc191123520 .anchor}Atmospheric gasScientific
objectives related to investigating the geochemistry of Martian
atmospheric volatiles, include determining the following:

-   
-   
-   

Composition, origin, and evolution of the Martian atmosphere through
time as well as the processes that have modified the atmosphere.
Concentration of trace organic gases, such as methane and ethane, their
variation in space and time, and their relationship to a possible
Martian biosphere.Transient photochemical gases, such as ozone, hydrogen
peroxide, and others, and their relationship to the oxidation of the
Martian surface.As discussed in Appendix II, the systematics of Martian
volatiles should be studied in two complementary ways: analysis of
atmospheric gas and analysis of gas released by the thermal
decomposition of rocks of various types and ages. Collected gas samples
could be utilized to determine the stable isotopic abundances, including
noble gases, and trace gas composition of the present-day bulk
atmosphere (Appendix II, IIB-1). Likewise, the thermal decrepitation
studies of solid samples could help to determine the history of the
composition of the atmosphere (Appendix II, IIB-3). However, ND-SAG has
concluded that determining the production/loss, reaction rates, and
global 3-dimensional distributions of key photochemically reactive
species is not easily possible using sample return, because the species
of interest are present in trace quantities, and the species degrade
relatively rapidly. The gas placed in the container on Mars would not be
the same as the gas received in the lab on Earth. Characterizing organic
gases to interpret possible biologic implications, although important to
Goal I (Appendix II; e.g. IA-4, IB-1, IB-3), may also encounter similar
difficulties in sample preservation. Thus, for the remainder of this
section, the scientific objectives are considered in the context of the
major inorganic gases, including the noble gases.

Our present knowledge of the Martian volatile system comes from previous
measurements by the 1976 Viking landers, and from analysis of gases
trapped in Martian meteorites. Those results show that that some
atmospheric species (e.g., N, H, Ar, Xe) have been isotopically
fractionated by atmospheric loss into space. Models of both continuous
loss and early episodic loss have been advanced (e.g., Pepin, 1991), but
the details of volatile loss remain largely unanswered. Atmospheric loss
also has occurred on other terrestrial planets, such as Earth. To
understand the specific atmospheric loss mechanisms, it is important to
know the initial isotopic compositions of these gas species. Such
knowledge may also indicate to what degree these volatiles were acquired
during the accretion of Mars and later degassed from the interior,
versus to what degree volatiles were added after accretion by, for
example, comet impacts.

Knowledge about initial isotopic compositions mainly derives from
analyses of volatiles trapped in solid samples, either ancient rocks
containing volatiles accreted with Mars, or in condensed phases such as
carbonates and hydrates, which represent major inventories of these
volatiles on Mars. Earlier atmospheric gases also could be trapped in
impact melts. The potential exists to use gaseous isotopes formed over
time through radioactive decay (e.g., ^40^Ar, ^129^Xe) and measured in
samples of different ages to characterize early Martian differentiation
and evolution of the atmospheric inventory. Ancient volatiles trapped in
Martian meteorites give hints of initial volatile compositions, but some
initial isotopic compositions (e.g., D/H, ^13^C/^12^C, light noble
gases) are largely unknown, as are details of variations in isotopic
compositions through Martian history, generated by volcanic degassing,
loss to space, climatic cycles, etc. The ^13^C/^12^C, ^18^O/^16^O, and
D/H isotopic ratios of atmospheric gases are important parameters in
understanding chemical equilibria among atmospheric and condensed
volatile phases, but these ratios are poorly known. Further,
measurements of various volatiles in solid samples (igneous and
sedimentary rock, chemical precipitates, impact glass, etc) could
elucidate the important volatile-containing phases within Mars and
possibly variations in these phases across Martian history and climatic
cycles. An understanding of the C, O, and S isotopic compositions in
condensed Martian phases could be important in determining formation
temperature and distinguishing biotic from abiotic chemical reactions
that produced such phases (e.g., Farquhar et al., 2000; Valley et al.,
1997).

Comparisons of isotopic compositions of volatile elements like C, O, H,
and S in various chemical forms and in different phases of returned
samples could give a potential wealth of geochemical information about
atmospheric and volatile interactions and evolution. The isotopic
compositions of such species are subtly changed when they undergo
chemical reactions or phase changes, and these isotopic differences may
elucidate these phases and processes and the temperatures involved. For
example, the isotopic composition of carbon differs in predictable ways
in carbonates precipitated from carbonate-bearing groundwater and in
equilibrium with atmospheric CO~2~. Further, such data could provide
information about genetic relationships among sulfur- and oxygen-bearing
phases, the oxidation pathways for compounds in the regolith that
involve atmospheric species with anomalous oxygen isotope compositions
(which could be affected by oxygen sinks), and the sources and mixing of
Martian sulfate. Although the isotopic compositions of these elements in
the present and ancient Martian atmosphere are important for such
considerations, their atmospheric compositions are poorly known. Solid
samples also are certain to contain noble gases produced by cosmic ray
bombardment of the Martian surface, and these have likely altered the
atmospheric noble gas composition over time.

In addition to what we know from Viking and study of the Martian
meteorites, MSL will carry an instrument (SAM) that is capable of
measuring many components of the Martian atmosphere, including the
isotopic ratios of Ar, N~2~, CO~2~ (both C and O), Kr, Ne, Xe, the
concentration of methane and sulfur gases, and the D/H ration in H~2~O.
The precisions and detection limits of SAM's capability in these areas
is summarized in Table 2 (Appendix V; data from Mahaffy, writ. comm.,
2008).

[]{#__RefHeading___Toc191123497 .anchor}Table 2 Planning aspects related
to a returned gas sample.

![](media/image2.pct)*Notes on Table 2: 1). More abundant Xe and Kr
isotopes are known more accurately, but the low abundance isotopes, with
the least accurate precision, are important in order to decipher the
starting compositions. 2). CAVEAT on the use of meteorites to interpret
gas chemistry:  Assumes gas trapped in* *Martian meteorites is the same
as the current* *Martian atmosphere.*

ND-SAG concludes that analysis of a returned Martian atmospheric sample
for Ne, Kr, CO~2~ and CH~4~ and C~2~H~6~ would confer major scientific
benefit (Table 2). Characterizing the initial Kr component in the
primitive atmosphere would require analytic precision beyond MSL's
capabilities. Understanding processes of exchange between CO~2~, CH~4~
and exchangeable crustal reservoirs of carbon, oxygen and hydrogen
requires highly precise stable isotopic measurements. A returned Xe
sample would provide an improved estimate of the initial atmospheric Xe
component and of minor components that have been added. However,
returned samples of Ar, N~2~, S gases and H~2~O would confer minimal
benefits relative to what we expect to learn from MSL. The abundance and
isotopic measurements of Ar and N~2~ achievable by MSL [in
situ]{.underline} would be sufficient to address the key open scientific
questions in those areas. The S gases and H~2~O have such low abundances
and high reactivity that they would not be expected to survive the
return to Earth in unmodified form. Appendix V explains the rationale
for these findings in greater detail.

## 

[]{#__RefHeading___Toc191123521 .anchor}DustDust is the pigment of Mars,
supplying the reddish hue to the Red Planet. Thick accumulations of dust
are a significant component of the Martian surface. The globally
extensive high albedo, low thermal inertia regions of Mars may contain a
meter or more of dust *(Christens*en, 1986). Intermediate albedo regions
like those visited by four of the five landed missions show a patchy
dust cover that is several cm thick in places. Even the low albedo
surface of Meridiani Planum includes isolated occurrences of dust in the
lee of obstacles as well as mixed into the regolith *(Yen et a*l.,
2005). This dust is carried aloft during seasons of atmospheric
turbulence, encircling the globe and then falling out over time onto all
exposed surfaces both natural and human-made. Despite the ubiquity of
dust and the multitude of orbital and surface analyses applied to it,
some of the details of its mineralogy and chemistry remain elusive.
Without these details, an important window into the weathering and
alteration history of Mars remains closed (see also MacPherson et al.,
2001; 2002), and questions about its potential hazard to human explorers
are left unanswered.

Beginning with telescopic observations, the bright regions of Mars were
recognized as rich in oxidized iron. Visible/near infrared (VNIR)
spectra are reasonably well matched by certain palagonitic tephras from
Hawaii \[Singer, 1982\], which are described as hydrated amorphous
silicate materials containing nanophase ferric oxide particles. The role
of water in altering the dust and/or its parent material has been
recognized in subsequent years with orbiter observations of spectral
features attributable to a water-bearing phase(s) (e.g., Murchie et al.,
1993) including the possibility of zeolite (Ruff, 2004). Thermal
infrared spectra provide evidence that a few weight percent of carbonate
minerals may be present in the dust (Bandfield et al., 2003).
Measurements by the MER rovers clearly show that sulfur is enriched in
the dust (Yen et al., 2005) and that virtually all dust particles, which
very likely are agglomerates, contain a magnetic phase (Bertelsen et
al., 2004) that probably is magnetite (Goetz et al., 2005). Although
Martian dust shows evidence for aqueous alteration, the presence of
olivine demonstrates that water did not play a dominant role in its
formation (Goetz et al., 2005).

## 

[]{#__RefHeading___Toc191123522 .anchor}Depth-resolved suiteSeveral of
the life-related MSR objectives assign high priority to returning
samples that contain reduced carbon. Because the surface of Mars is
oxidized, organic matter might exist only at depth. Even if MSR is
unable to acquire organic-bearing samples, it is important to acquire
data in order to model the preservation potential of reduced species and
thereby determine where organic matter might be accessible. The organic
carbon measurements of the Viking landers indicated clearly that the
surface (regolith) of Mars is oxidized to such an extent that any
volatile organic components are being continuously destroyed. Although
organic carbon compounds are raining down continuously from carbonaceous
chondrites, cometary material, interplanetary dust particles, and
micrometeorites (Flynn and McKay, 1990), the Viking experiments found no
trace of them (Klein, 1978, 1979). It is hypothesized that prebiotic
compounds that are relatively nonvolatile have been destroyed. Although
there is indication that reduced organic compounds survive in the parent
lithologies of Martian meteorites (Steele et al., 2007 and references
therein), chemical modelling suggests that the depth of the oxidized
surface layer is of the order of cm to several meters (Dartnell et al.,
2007). Various oxidizing agents have been proposed, including OH, HO~2~
and H~2~O~2~ species produced by photolysis of atmospheric water vapor
(Zent and McKay, 1994; Zent et al., 2003). These species could form
complexes with metals in the Martian regolith to create peroxy radicals.
Another source of oxidation could be UV-silicate interactions that trap
oxygen, resulting in highly oxidized dust and soil particles, or perhaps
even unknown "super-oxidants\".

Models indicate that impact "gardening" of the regolith could mix the
oxidant(s) to depths of a few meters (Zent, 1998). Kminek and Bada
(2006) concluded that over geologic time scales, ionizing radiation
destroys organic matter (specifically, amino acids) to depths of at
least 1.5 to possibly 2 m, although Dartnell et al. (2007) have shown
that this effect is intrinsically linked to the amount of shielding of
organic materials. Permeability-based modelling estimates that oxidants
penetrate to depths between 10 cm to 5 m in the regolith, depending on
the model, time of exposure and the nature of the regolith material
(Bullock et al., 1994). Thus it might be desirable to obtain samples
from as deep as 3 m into regolith. Although it would be preferable to
collect a set of samples from several depths, an alternative would be to
collect a single larger sample from the maximum depth reached. Regarding
bedrock and detached rocks, the depth of oxidation presumably depends
principally on time and the permeability and reactivity of the rock.
Analyses of RAT holes during the MER mission indicate that Hesperian-age
basalts have remained largely unoxidized within \<1 cm of their surfaces
(McSween et al., 2006). Data from Martian meteorites has shown that
reduced carbon could be detected within carbonates from 3.6Ga on Mars
(Steele et al., 2007, Jull et al., 1997, Flynn et al., 1998).
Sedimentary bedrock at the MER Meridiani site has been oxidized to
greater undetermined depths. A rock core at least several cm in length
from an outcrop would allow the change with depth in composition
(organic, inorganic, oxidation state) due to surface oxidation to be
determined.

An important strategic consideration is that MSL (2009) and ExoMars
(2013) will both collect data that will either increase or decrease the
priority of the depth-resolved sample suite (see Fig. 1). MSL will carry
a highly sensitive organic detection system (the SAM instrument) and
obtain samples by drilling 5 cm into rocks and wheel-trenching up to
tens of cm into regolith. ExoMars will also carry a very sensitive
organic detection instrument (MOMA) and an oxidant detector (MOD). They
will characterize gradients with depth in oxidation state, as well as
the organic carbon, using so-called Vertical Surveys (VS), obtaining
samples at 50-cm depth intervals from the surface down to 2 m. Two such
VS acquisitions are planned for the nominal mission.  If MSL discovers
organic carbon at shallow depths in either rocks or regolith, the
importance of a depth-resolved set of samples for MSR would decline. If
MSL fails to detect organic carbon in shallow samples, but ExoMars
detects it in deeper samples, the importance would increase
substantially.

![](media/image3.png){width="3.6770833333333335in" height="2.71875in"}

*[Figure 1.]{.underline} Importance of sampling to a depth of 2-3 m by
MSR, given various potential scientific results from MSL and ExoMars.*

## 

[]{#__RefHeading___Toc191123523 .anchor}OtherOther types of samples
would be of interest if encountered by an MSR sampling rover, but it
would likely be hard to target the mission to acquire them. It is
perhaps useful to think of them as samples of opportunity.

[Impact Products]{.underline}. Breccias might sample rock types that are
otherwise not available in local outcrops and thus might be the most
valuable. The utility of breccias in the Apollo collection has been
demonstrated repeatedly (e.g. James et al., 1989). Impact excavation is
the most plausible means of producing rock fragments on Mars, so it is
possible that rocks from deeper levels in the crust might only be
sampled in breccias. Diversity would be a major goal in collecting
returned samples, and breccias often contain diverse materials. Impact
melts would be highly significant for understanding the bombardment
history. Testing the idea of a late heavy bombardment is particularly
crucial and could be accomplished only by dating impact melts.
Admittedly, these are not easy to identify and all the basins are
filled, but there may be places where craters have excavated below
sedimentary or volcanic fill (e.g. perhaps Hellas?).

[Volcanic Products]{.underline}. Volcanic tephra is also likely to be
encountered as fine-grained components of the regolith, or as layers and
beds of tephra from nearby or faraway sources (e.g., Wilson and Head,
1994; 2007).  Such samples would supply important information on the
mineralogy of explosive volcanic eruptions, grain-size information
critical to the interpretation of volcanic eruptions and tephra
transport, and ages of explosive eruptive phases of the history of Mars.
Volcanic glasses would also represent a unique opportunity to sample
primitive magmas from the mantle, as demonstrated on the Moon (e.g.,
Delano, 1986).

[Meteorites]{.underline}. Several iron meteorites have been found at
both MER landing sites (Squyres et al., 2006), and a few small cobbles
in Meridiani have been suggested to be chondrites. If the residence time
of a meteorite on the surface could be determined, the alteration
histories of materials with well-known mineralogy, chemistry, and
texture could give useful information about the rate of weathering (e.g.
Ashely et al., 2007). It may be possible to do the same with a sample of
fresh basalt that has been excavated to the surface. Obviously,
allocating precious return mass to a meteorite would require a strong
justification for the hypothesis being tested.

[]{#__RefHeading___Toc191123498 .anchor}Table 3 Summary of Sample Types
Needed to Achieve Proposed Scientific Objectives.

![](media/image4.pct)

Note: Priorities are expressed as relative High, Medium, and Low. Where
there is no entry, the sample type would not make a meaningful
contribution to the scientific objective.

# 

## 

[]{#__RefHeading___Toc191123524 .anchor}FACTORS THAT WOULD AFFECT THE
SCIENTIFIC VALUE OF THE RETURNED SAMPLES[]{#__RefHeading___Toc191123525
.anchor}Sample sizeThe mass of the individual samples and the total mass
of the returned collection should be sized so as to provide enough
material for (1) preliminary characterization, (2) life detection (LD)
and biohazard (BH) tests needed for planetary protection, (3)
allocations to scientific investigations, and (4) representative
reserves to be archived for future investigations. We need to plan for
all future uses of sample material in order to determine the optimal
sample size.

[Preliminary examination]{.underline}

Preliminary examination is necessary to make decisions on what actions
to take with each sample. The samples from the Apollo, Antarctic
Meteorite, Cosmic Dust, Stardust, and Genesis collections provide
excellent precedents for planning this step for samples from Mars.
Accordingly, the discussion here is based on nearly 30 years of
experience gained from such activity at Johnson Space Center. As part of
preliminary examination, techniques that are non-destructive or require
minimal sample mass (e.g., Raman spectroscopy, XRF, FTIR spectroscopy,
laser desorption-mass spectrometry, optical microscopy, SEM, EMPA,
TOF-SIMS) could be used to classify and characterize the samples (table
5). The use of non-destructive techniques would maximize the quantity of
sample available for subsequent investigations by the planetary science
community. In addition, thin sections could be prepared and curated as
is done for lunar and meteorite samples, using standard thin sectioning
methods for small rocks and coarse fines. Focussed ion beam milling
would be used to prepare small sections if necessary; this technique is
being used for all kinds of samples from the lunar (Noble et al., 2007),
meteorite (Goldstein et al., 2006), pre-solar grain (Stroud et al.,
2006), Stardust (Nakamura-Messenger et al., 2007) and Mars (Clemett et
al., 2006) communities. For very small samples, ultramicrotomy would be
used to prepare thin slices that could be distributed to multiple
scientists (Figure 12 in Nakamura-Messenger et al., 2006). Destructive
techniques used during preliminary examination for sample preparation
should be limited to those required to prepare the thin sections and
slices by these three techniques.

[Life detection and biohazards screening and testing]{.underline}:

The most recent analysis of the test protocol for life detection and
biohazard testing for returned Martian samples was published by Rummel
et al. (2002; based on technical analysis done in 2000-01). There have
been significant improvements in analytic methodology since then, so the
list of analytical methods and the required sample sizes must be updated
substantially (for example, many techniques could be performed on a thin
section, and the more extensive destructive techniques could be
performed on sample splits on the order of 50 to 100 mg; *Glavin et al.,
2006; Elsila et al., 2005)*. These tests would be grouped into two
categories: non-destructive (e.g., Raman and confocal Raman
spectroscopy, XRF, FTIR spectroscopy, laser-desorption mass spectrometry
(LDMS), and 3D tomography) and destructive techniques designed to look
for carbon compounds and their molecular structures (e.g. GC-MS, LC-MS,
Py-GC-MS LAL, TOF-SIMS), and nucleic acids via amplification techniques
(i.e. PCR). Since the volatile inventory is critical for assessing the
presence of extant or extinct biomass, we would need some way to
determine the abundance of the four light elements (C, H, N, and S)
likely to co-occur in biosynthesized organic matter. In addition, the
draft test protocol specifies plant and animal challenge tests, which
would also be destructive.

The total amount of sample to carry out the life-detection and biohazard
tests was estimated by Rummel et al. (2002) as 15-25 g, although has
sometimes been represented subsequently as \~10% of the returned sample.
Given the near certain that the total quantity of returned sample would
be relatively small, it is important that only the amount absolutely
needed be used for such purposes. We need to plan for the sample size
and packaging that would be needed to carry out the hazard assessment
protocol.  A specific open issue is how to achieve statistically
significant subsampling of the returned collection, particularly
involving the rock samples.

There are two alternative strategies for allocating enough sample mass
for these tests. Both strategies need further discussion by the
community.

1.  
2.  

Collect most of the incremental mass in the form of larger regolith
samples (e.g. one or more samples \>30 g). Since the regolith is
composed of components derived from multiple geologic sources, the
regolith samples would contain a mixture of rocks, dust, volcanic ash,
ejecta, decomposed bedrock, etc. Moreover, all of these have interacted
with the Martian atmosphere and obliquity-driven climate change. In
short, they may represent an integration of Martian surface geologic
processes. This might best kind of sample in which to test for the
possibility of forms that proliferate on the surface during intermittent
warmer/wetter intervals, and then become wind-blown constituents of the
regolith. If there are significantly warmer periods during extreme
obliquity there may be the possibility of intermittent proliferation of
a surface microbial community that is adapted to long periods of
inactivity.  Searching for spores or biopolymers (something equivalent
to extracellular polymeric substances) could be a goal for regolith
studies. If there is an extant microbial organism or community on Mars,
it would need to be encased in desiccation, oxidation, and radiation
resistant molecules. This collection plan could allow for processing
individual samples through the entire test protocol. Collect rock
samples 1-2 g above what would be needed for scientific purposes, so
that a split could be taken from each rock for destructive hazard
assessment testing. The hazard assessment protocol consists of a package
of tests, each of which would have different mass requirements. Thus, in
this strategy it would be possible to run individual samples through
some of the tests, but other more mass-intensive tests (e.g. plant
growth experiments?) may require the use of composite samples. As input
to future more detailed discussion of this topic, ND-SAG offers that the
rocks themselves could be the most probable habitat for Martian life.
The protective coating of the rock could help retain water, protect the
interior from radiation, and reduce exposure of the endolithic (rock
interior) habitat to surface oxidants. Thus, ND-SAG would be
uncomfortable with a strategy that did not test for biohazards in at
least some of the rocks. 

Many of the non-destructive techniques could be performed on a thin
section. Of the more extensive destructive techniques sample splits on
the order of 0.05-0.5 g would be needed per analysis depending on the
technique and sample composition. Given these mass estimates and
allowing for multiple analyses of several different rock sub-samples, an
estimate of 2 g for these tests would be required. This estimate may be
more or less depending on the rock type, initial screenings, and changes
in the analytical requirements as instrumentation advances. If less is
used, that mass could be available for either the scientific
investigations or future measurements (see ranges in Table 5).

[Research requests through principal investigators]{.underline}:

In order to estimate the mass of rock sample that must be collected to
meet analytical needs for various scientific investigations, we can turn
to experience gained from the Martian meteorite collection. In 1994, a
12.02 g meteorite, now referred to as QUE-94201, was found in the Queen
Alexandra Range of the Transantarctic Mountains. This sample is a
basaltic rock that also contains hydrous minerals (phosphate), and
evaporites. Both of these mineral types could provide information about
Martian volatiles and igneous processes. Since 1994, this sample has
been subdivided into 63 splits, including 27 bulk samples (4.416 g) for
destructive analysis, and 13 thin sections (using 2.2 g). To date 23
principal investigators have studied the first set of splits
(sub-samples), and 29 principal investigators examined splits that were
created subsequently. In addition, 5.16 g of material is still available
for study using new techniques or by a new generation of scientists. Of
relevance to any sample return mission is the attrition measured during
sample processing and in the case of QUE 94201, 0.346 g (or \~3%) were
lost during processing.

[]{#__RefHeading___Toc191123499 .anchor}Table 4 Subdivision history of
Martian meteorite QUE 94201

+-------------+-------+----------------+------------------------------+
| Type        | Mass  | Techniques /   | Information gained           |
|             | (g)   | notes          |                              |
+-------------+-------+----------------+------------------------------+
| a\)         | 4.416 | SEM, TEM, AMS, | Samples allocated to 23 PIs  |
| Destructive |       | INAA, TIMS,    | for studies of: Bulk         |
| analysis    |       | stable isotope | composition (INAA)           |
|             |       | MS, noble gas  |                              |
|             |       | MS, XANES,     | Crystallization age (Lu-Hf,  |
|             |       | EMPA           | Rb-Sr, Sm-Nd, K-Ar, U-Pb)    |
|             |       |                |                              |
|             |       |                | Differentiation age (Hf-W,   |
|             |       |                | Sm-Nd)                       |
|             |       |                |                              |
|             |       |                | Exposure ages (^3^He,        |
|             |       |                | ^21^Ne, ^38^Ar, ^81^Kr,      |
|             |       |                | ^10^Be, ^26^Al, ^36^Cl,      |
|             |       |                | ^14^C, ^53^Mn)               |
|             |       |                |                              |
|             |       |                | Rock-atmosphere interactions |
|             |       |                | (C, S, O, H isotopes)        |
+-------------+-------+----------------+------------------------------+
| b\) Thin    | 2.2   | SEM, TEM,      | 13 thin sections produced    |
| section     |       | SIMS, XANES,   | and studied by 29 different  |
| production  |       | EMPA, optical  | PI\'s from many scientific   |
|             |       | microscopy     | disciplines; first section   |
|             |       |                | allowed classification       |
+-------------+-------+----------------+------------------------------+
| c\)         | 0.372 | SEM, magnetic  | Textural analysis, rock      |
| Non-        |       |                | magnetization                |
| destructive |       |                |                              |
| analysis    |       |                |                              |
+-------------+-------+----------------+------------------------------+
| d\) Still   | 5.160 | Includes mass  | Sample material still being  |
| available   |       | from c)        | allocated 12 years later     |
| for study   |       |                | using new techniques and by  |
|             |       |                | next generation of planetary |
|             |       |                | scientists                   |
+-------------+-------+----------------+------------------------------+
| e\)         | 0.346 | Material lost  |                              |
| attrition   |       | during         |                              |
|             |       | processing     |                              |
+-------------+-------+----------------+------------------------------+

*Abbreviations: SEM -- scanning electron microscopy; TEM -- transmission
electron microscopy; EMPA -- electron microprobe analysis; INAA --
instrumental neutron activation analysis; AMS -- accelerator mass
spectrometry; TIMS -- thermal ionization mass spectrometry; SIMS --
secondary ion mass spectrometry; XANES -- x-ray absorption near edge
structure; MS -- mass spectrometry.*

The manner in which QUE 94201 was subdivided and the number of
investigators involved provides a relevant analog situation that might
be expected for Martian samples of similar size in a collected suite of
rocks such that a rock sample could be divided into subportions that are
subsequently divided for various analyses. This would allow application
of single analytical techniques on one portion of a sample or multiple
analyses for techniques that have low mass requirements that may reveal
spatial distributions. Also, an estimate of mass required for
destructive techniques part of scientific investigations is provided by
the QUE 94201 example: the average mass of QUE 94201 used for
destructive analysis by individual PIs is 0.2 g (based on analysis in
Table 1). Therefore, if 12-15 PIs were allocated material from an
individual sample from a suite, that would require \~ 2.5 to 3.0 g.
Notably, QUE 94201 was not tested for organic composition. Consequently,
either additional sample mass would be necessary for organic tests for
science investigations that extend beyond life-detection and biohazard
screening by the SRF, or all the destructive tests applied would be
limited to a select number of techniques determined based on the sample

[Sizing the Rock Samples]{.underline}

Adding up all of the currently understood proposed uses of the returned
Martian samples, the minimum size for the purpose of the mission's
scientific objectives would be about 8g for both rock and regolith
samples. If we assume an additional 1-2g of sample needs to be taken
from each rock and regolith sample to support biohazard testing, a good
standard sample size would be 10g each. Alternatively, if most of the
biohazard testing is to be done on regolith samples, it may be possible
to standardize on 8g rock samples, and 20g regolith samples. A very
similar conclusion (10-20g samples) was reached in Appendix III by
MacPherson et al. (2005).

Occasionally, rocks and sediments exhibit fabrics and textures at the mm
to cm scale that are highly diagnostic of their formation and/or
subsequent alteration. For example, the MER rover Opportunity documented
the shapes and sizes of both grains and laminations that were consistent
with the former presence of a shallow playa lake (Grotzinger et al.,
2005), and these features are of a scale that is best observed in larger
samples. On Earth, other rock types (e.g., igneous cumulates and high
grade metamorphic rocks) also locally exhibit large-scale textures
having high diagnostic value (e.g. foliation, flow features, layering,
segregations, etc.). Having the capability of collecting one or more
samples of about 20 g may help to correctly interpret such features.
This may be achievable from two 10-g samples collected adjacent to each
other (e.g. 1-2 cm apart). Alternatively, we may need to put a priority
on documenting larger-scale textures in situ, so that the local context
within heterogeneities larger than the sample size is documented.

[Special note about the size of sedimentary rock samples]{.underline}

The minimal mass of samples of sedimentary deposits depends on the
specific nature of the intended investigation. Experience from Earth
suggests that sedimentological and stratigraphic studies normally need
at least 5 g per sample in order to have a sufficient area of bed
surface and internal structure to observe and document orientation of
stratification, sedimentary structures, grain-size distributions, grain
contacts, and mineral composition. Although we don't know the
concentration of organic molecules that might be present in returned
Martian samples, studies on terrestrial samples commonly involve 10-20 g
per sample. Solvent-extractable organic compounds are present in many
samples in low concentrations that approach instrumental detection
limits. In such cases, 1-2 g of sample is needed per measurement;
however, multiple analyses are commonly required to verify molecular
structures. Careful documentation of geological context is required for
samples of sedimentary materials in order to relate their interpretation
to the regional scale.

[Sizing the regolith sample(s)]{.underline}

The likely diversity of regolith materials, particularly at a
geologically complex landing site, means that a number of separate
regolith samples e.g. 3, each of 1 to 25g, are preferred. A regolith
sample of this mass is also likely to be appropriate for biohazard
testing at the Sample Return Facility. More detailed information on
sampling involving trenching or drilling to depths on the order of tens
of cm is given in Appendix II. [Further discussion needed]{.mark}.

[Sizing the dust sample(s)]{.underline}

Given the global homogeneity of dust on Mars *(Christensen et a*l.,
2004*; Yen et a*l., 2005), a single sample from anywhere would likely be
representative of the planet as a whole. However, because relatively
pure dust deposits often are only mm thick, scooping a pure sample may
be challenging in some locations. It is recommended that enough material
be acquired to satisfy the needs of the various scientific
investigations, as well as to provide an amount material sufficient to
allow its potential hazard to humans and machines to be assessed. As
discussed in Appendix III, for human toxicity studies, we need to plan
for enough material to be able to conduct intratracheal, corneal, dermal
and ingestion studies that would allow assessment of toxic effects. Past
experience with lunar sample material and with lunar stimulant has shown
that 20 grams is likely to be sufficient, but these tests could be
carried out with either dust or regolith. The fraction of interest for
toxicity studies is in the \<20 μm size fraction, and especially the \<5
μm fraction.

[]{#__RefHeading___Toc191123500 .anchor}Table 5: Generic plan for mass
allocation of individual rock samples

![](media/image5.pct)[Sizing the gas sample(s)]{.underline}

Because of the wide range of concentration of the various gas species in
the Martian atmosphere, the quantity of atmospheric gas needed for
measurement varies greatly among the different major species (Table 2).
Also, higher analytic precision would be possible with larger samples,
and multiple analyses of most species would be desirable.  Consideration
should also be given to possible gas sample contamination during return
to Earth and distribution of sub-samples of gas to various analytic
labs. We suggest that a minimum returned gas sample should be 1
cm^3^STP, or \>100 cm^3^ ([THIS FIGURE IS A TRIAL BALLON THAT NEEDS
DISCUSSION]{.mark}) at Mars ambient pressure. However, for the four high
priority measurements listed in Table 2, it would be possible to make 10
determinations with a 20 cc sample of gas at ambient pressure. This
atmospheric sample could be returned either within its own dedicated
container, as head space gas within a container for solid samples, or
both. Special consideration must be given both to hermetically seal
these containers to insure that the gas would not be contaminated during
the sealing and return process, and to design a mechanism for efficient
gas removal on Earth.

Atmospheric species probably would occur in some form and in widely
varying concentrations in nearly all returned solid samples, either as
trapped volatiles or as condensed phases such as hydrates, carbonates,
or sulfates. One important property of Martian rocks is that several
components are present, including primitive trapped gases and
atmospheric components, and these must be resolved.  This is important
for atmospheric gases, as these may have been incorporated at different
times (paleoatmospheres) and may provide samples of the evolving Martian
atmosphere.  Therefore, the precision of the measurements must permit
these components to be resolved. Unfortunately their concentrations are
typically much lower in rocks from Mars, compared to those from Earth.
For example, in nakhlite NWA998, the observed gas release is typically
0.2 ppm of N per temperature step, giving an uncertainty of \~0.5‰ from
zero to +150 (Mathew and Marti, 2005). The release of xenon (^132^Xe 0.1
to 5 e^-12^ cm^3^/g) gave (one sigma) precision of 1% for rare isotopes
(^124^Xe, ^126^Xe) and \< 5‰ for the abundant isotopes (e.g. ^131^Xe). 
When highly variable anomalies, due to radiogenic (^129^Xe), fission
(e.g. ^136^Xe) and spallation components (e.g. 126Xe), are observed the
uncertainties increase. ND-SAG concludes from all of this that it is not
feasible to set the minimum sample size of the rock samples based on
their proposed use in gas-release experiments---we simply don't have
enough information to know how to set the thresholds.

[A final note]{.underline}

As Deep Impact has demonstrated, a small amount of material may make it
possible to make a "preliminary investigation", and we should not
underestimate what can be accomplished with samples smaller than ideal.

## 

[]{#__RefHeading___Toc191123526 .anchor}Number of Samples. Natural
materials are heterogeneous at scales ranging from atomic to planetary.
Mineralogical, geochemical, biogeochemical, and morphological properties
would be assumed to vary among samples depending on the temporal and
spatial distribution of processes active on Mars. In many studies,
characterization of heterogeneities could provide as much information
about processes as the specific characteristics of a given sample. Thus,
for maximum scientific benefit, Mars sample return missions would need
to capture as much of this diversity as reasonable through careful
selection of both landing sites and samples from each site.

The number of samples needed to capture appropriate heterogeneity
depends on the local Martian environment and geological history. Field
experience on Earth has taught us the importance of acquiring
sufficiently diverse samples to evaluate whether or not a specific
result is representative as well as to extrapolate interpretations of
processes from variations among and within samples. In many cases,
carefully selected suites related rocks allow one to reasonably
evaluate: 1) how representative each sample may or may not be of the
geologic unit; 2) the consistency of processes creating and altering the
samples; and 3) abundances of specific attributes such as minerals and
geochemical signatures.

Without pre-characterization of a specific Martian site, it is not
possible to define the number of samples required to capture local to
regional diversity in geological materials. However, an estimate of
sample number is necessary for mission planning. For many studies, a
suite consisting of about five to eight samples would be sufficient for
a first-order evaluation of the heterogeneity of units, the consistency
of processes, and the abundances of representative features. Two
examples demonstrate this. In Endurance Crater, Mars, the analysis of
seven stratigraphically distributed sites in the Burns Formation allowed
the Opportunity Rover team to identify several significant diagenetic
events, some of which were associated with variations in groundwater
(McLennan et al., 2005). In a second example, APXS analyses of a eight
separate samples of alkaline volcanics revealed that they were formed
under different conditions or from very different starting composition
compared to the bulk of Martian rocks; thus, shedding new insight on the
complexity of the Martian interior (McSween et al., 2006). In both of
these examples, a smaller number of the "right" samples could have
provided sufficient information for the resulting interpretations, but
pre-selection of the smaller set of samples would have required
significant characterization. Thus, for Mars sample return, either
extensive in situ characterization capabilities would be needed or a
suite of at least five to eight samples should be collected from each
geological unit. More samples would provide better information, but a
suite of five to eight samples should provide sufficient diversity to
provide substantial scientific return.

[Quantity of samples to be cached by MSL]{.underline}

The MSL cache is designed to accept rock samples 0.5--1.5 cm in size
provided by MSL\'s soil scoop, collected over 5--10 separate caching
events (Karcz et al., 2007). The cache will have mesh sides to allow
fines to filter out, leaving behind rocks. The strategy for employing
the scoop to acquire either individual targeted rocks, or rock-bearing
regolith would depend on further experience with prototype scoops (note
that the volume of the scoop is roughly half the volume of the cache).
The empty cache is specified to have a mass less than 52 g. However, the
mass of the latest revision of the design (as estimated by the CAD
software) is 29 g (Karcz, writ. comm., 01-07-08). A draft specification
(as of this writing) is for the mass of the cache container when full to
be 200 g or less. Because the mass of the contents will be uncertain, it
is likely that the science team will fill it to somewhat less than
capacity\--to, say, 180 g instead of 200 g.

Table 6 summarizes some possibilities regarding sample number and
overall mass.  For the purpose of this table, both rock and regolith
samples are assumed to be 10 g each (as per Table 5), and that
encapsulation mass is assumed to be an additional 10 g per sample.  In
Case A (MSL cache would be recovered), the return of 20 rock, three
regolith, one dust and one gas samples, along with the MSL cache, would
lead to a total returned mass of 670 g, of which 365 g would be
samples.  If 500 g is a firm limit for the total returned sample mass,
the number of rock samples would have to be reduced to 12. In Case B (no
MSL cache), the mass allocated for the cache could be used for
additional rock and regolith samples of the same aggregate size.  This
could allow the number of rock samples to be raised to 28, and the
number of regolith samples to four; in this model the total amount of
sample mass would drop somewhat to 325 g.

[]{#__RefHeading___Toc191123501 .anchor}Table 6 Summary of number, type,
and mass of returned samples.

![](media/image6.pct)

[Some implications/questions]{.underline}:

-   
-   
-   

## 

Would a total mass of 670 g inside the returned container (instead of
500 g) break the mission? Because it might not be possible to determine
whether the MSL cache is recoverable until MSR gets there (for example,
MSL may end its life in an inaccessible location), it would be
advantageous for MSR to carry enough sample vials for the full set of
samples described in Case B of Table 6, not just those in Case A.  That
way either scenario could be accommodated. The value of the MSL cache
would need to be explicitly compared to an incremental eight rock and
one regolith sample having a known context and far better
curation\--these are mass-equivalent.  This comparison could be
meaningfully made only after the cache has been loaded and the MSL
science team knows its contents.[]{#__RefHeading___Toc191123527
.anchor}Sample Encapsulation. For several reasons, the packaging of
individual samples on Mars emerged as a central priority elucidated in
this study, a conclusion also reached by MacPherson et al. (2005).

-   
-   
-   
-   

[Avoid commingling of samples]{.underline}. First, cross-contamination
would likely occur without encapsulation and it would degrade the
scientific value of samples, particularly if samples from different
sites are mixed. Mixing would be a particular problem for weakly
lithified and friable samples that may break apart during transport to
Earth. [Retain volatile components]{.underline}. In addition, hydrous
materials that are not maintained at Mars ambient conditions might
dehydrate and form sulfur-bearing fluids that could readily react with
other samples and the container. [Sample labelling for linkage to
original field context]{.underline}. Individual samples must retain
their identities after they are returned to Earth. A friable sample
would lose much of its identifying characteristics if it breaks into
multiple pieces during transport. It is imperative that the samples be
linked to their collection sites even if the sample's physical and
chemical integrity are altered during transport.[Maintain sample
mechanical integrity]{.underline}. Several investigations would require
that the samples' macroscopic structures, microscopic textures and
mineralogical spatial relationships be preserved during collection and
transport. The samples' mechanical integrity must be preserved as well
as possible. This is a particular concern for friable sedimentary rock
samples that would be a major priority for MSR. Aqueous sediments could
exhibit fabrics and textures at the mm- to cm-scale that are highly
diagnostic of their formation and/or subsequent alteration. For example,
the MER rover Opportunity documented the shapes and sizes of both grains
and laminations that were consistent with the former presence of a
shallow playa lake (Grotzinger et al., 2005). Much of the sulfate-rich
bedrock at the Opportunity site appears to be weakly cemented and
therefore seems prone to fragmentation that might destroy its valuable
sedimentary textures.

The minimal sample encapsulation would be different for different
investigations and rock types. Investigations related to organic
chemistry, water, and other volatile components would require the most
stringent encapsulation procedures in order to minimize any organic
and/or biological cross contamination. These investigations would
require hermetically sealed containers. In addition, rock samples that
contain hydrous phases would require containers in order to prevent
fluids from escaping and reacting with other samples. The samples of
granular materials (regolith and dust) obviously would require at least
some form of mechanical packaging in order to retain their identity as a
sample. Although it is a scientific priority that all samples would be
encapsulated, it would not be necessary for scientific purposes that
they all have airtight seals.

Encapsulation is a particular issue for sedimentary rock samples. Some
chemical and siliciclastic sediments are permeable and/or fragile and
therefore could be highly susceptible to contamination and degradation
during acquisition and transport. Many of these samples have the
potential to break, disaggregate, dehydrate, and devolatilize. In
addition, iron oxide and phyllosilicate materials, in particular, could
adsorb volatile contaminants. Sample-to-sample contamination by water
and/or organic compounds is a serious concern. Consequently, gas-tight
encapsulation in inert containers is critical for samples of sedimentary
materials.

An engineering trade to be evaluated would be whether a single airtight
design should be used for all of the samples, or whether mass could be
saved by having some vials that would be airtight and some that would be
only "dust-tight".

## 

[]{#__RefHeading___Toc191123528 .anchor}Sample acquisition system
prioritiesIn order to attain the full scientific value of rock samples,
the sample acquisition system must be able to achieve the following:

-   
-   
-   
-   
-   

Sampling both the weathered exterior and unweathered interior of rocks.
The ability to sample a continuous stratigraphic sequence of outcrops
(e.g. the Burns Cliff at Meridiani Planum).In the case of rocks in
outcrop with differential hardness, the ability to sample both
less-resistant beds and more-resistant beds.Relate the orientation of
structures and textures in samples to those in outcrop surfaces, bedding
planes, stratigraphic sequences, and regional-scale geologic
structures.Maintain the structural integrity of samples.Given the sample
sizes discussed in this report, these priorities would be best served
with a small arm-mounted coring device (this sampling system was judged
to be essential by MacPherson et al., 2005). An example geometry that
would be of the right size is a small core of about 1 cm in diameter and
2 to 3 cm in length (how to optimize these parameters is still under
discussion). To distinguish this from larger drills with depth
capability of 2-3m, we refer to as a mini-corer.

The simplest way to sample granular materials, such as regolith and
dust, might be using a scoop. However, it may be possible to engineer a
mini-corer so that it could also be used to sample granular materials.

[]{#__RefHeading___Toc191123502 .anchor}Table 7 Science Priorities
Related to the Acquisition System for Different Sample Types.

![](media/image7.pct)

## 

[]{#__RefHeading___Toc191123529 .anchor}In situ measurements for sample
selection and documentation of field context. The scientific value of
MSR would depend critically upon the ability of the mission science team
to select wisely the relatively few samples that could be returned, and
on the degree to which the field context of these samples is known. In
order to achieve these two functions, the MSR sample acquisition rover
must be able to perform certain remote and *in situ* measurements.

ND-SAG has found that the instrument needs for MSR would be different in
the two scenarios listed below:

-   
-   

Case A. The MSR rover either goes to a previously unvisited landing
site, or it gets \'off the beaten track\' of a previously visited site.
In this case, both sample selection and documentation of context would
need to be done.Case B. The MSR rover "follows in the footsteps" of a
previous rover that has already established the field context and
identified the exact materials to be sampled. For Case A, five
measurements are important to support the collection of samples that
could be used for a wide range of scientific objectives: 1) high quality
color panoramic imaging would be essential to identify samples of
interest and to determine their local geological context (e.g.,
Grotzinger et al., 2005). 2) A microscopic imager that examines rock and
sediment textures for clues about processes and environments of
formation would also be essential. In addition, microbially induced
textures are one of the key indicators of life (e.g., Herkenhoff et al.,
2004). 3) The mineralogy would need be determined to discriminate one
rock from another and to establish geologic context of the samples
(e.g., Christensen et al., 2004). Minerals reflect the processes and
conditions associated with the formation of geologic materials. For
example, understanding compositional variability in the igneous sample
suite would require rocks that contain a range of minerals, such as
olivine, pyroxene, feldspar, and oxides. Phyllosilicates, sulfates,
carbonates and silica-rich minerals are excellent for retaining evidence
of aqueous processes and evidence of habitable environments and life. 4)
Measurements of elemental abundance have been critically important
during the MER mission (e.g., Ming et al., 2006; McSween et al., 2006)
and would be essential in understanding the range of variability within
a field site, and in identifying the effects of unusual geologic
processes. This information would be key to both sample selection and
documentation of context. 5) Reduced carbon measurements would be
centrally important to understanding prebiotic chemistry, habitability,
and life (e.g., Schopf, 1983), therefore reduced carbon should be
measured during the sample selection process. Although we could
certainly detect reduced carbon in returned samples to better than 1
ppb, ppm-level sensitivity may be sufficient for screening for sample
selection on Mars. The SAM instrument on MSL and the Urey and MOMA
instruments on ExoMars will presumably give us important guidance on
this after 2010. Finally, a rock abrasion tool would be essential to
characterize the rocks adequately. Because many rocks on Mars have dusty
or weathered surfaces, correctly determining the characteristics of the
underlying rocks would require access to fresh surfaces.

[]{#__RefHeading___Toc191123503 .anchor}Table 8 Rover-based Measurements
to Guide Sample Selection.

![](media/image8.pct)

*Notes: Case A -- MSR gets \'off the beaten track.\' This assumes that a
future MSR would go to either a fresh site, or outside the area studied
by a previous rover, where understanding the geologic context still
needs to be done. Case B -- MSR follows the tracks of a previous rover,
which has documented the context.*

For Case B, ND-SAG has concluded that the payload could be reduced to
the following two instruments: color stereo imagery and microscopic
imagery. In this case, the MSR rover would not need to determine the
geologic context and identify the materials to be collected - the prior
mission would have achieved these tasks. However, ND-SAG also concludes
that Case B has substantial risk, and it is not endorsed unless this is
the only way the mission could be done. For a variety of reasons it may
not be possible for the MSR rover to follow the tracks of the previous
rover. In addition, MSR would not have enough functionality to make
excursions off the previous rover traverse, which may be desirable to
follow-up on unexpected results, including from the previous mission.
The Case B rover would have minimal analytical capabilities for an
extended mission after the MAV leaves. Finally, if the MSR rover follows
another rover that is neither as clean nor as sterile as the MSR rover,
important implications arise involving planetary protection and
contamination control, and these should be evaluated further.

## 

[]{#__RefHeading___Toc191123530 .anchor}Temperature. The issues related
to temperature sensitivity of Martian minerals and organics were
reviewed in great detail by MacPherson et al. (2005; see Appendix III)
and so are not repeated here. At that time, the science community
expressed significant concerns about sample degradation at temperatures
above 0°C, and if anything, the scientific accomplishments of the Mars
program over the past three years appear have intensified those concerns
(e.g. Clark et al., 2005; Bibring et al., 2006; Peterson et al., 2007).
The perceived effects of temperature on achieving science goals are
summarized in Table 9.

Certain chemical species that would have great science value for MSR are
also sensitive to temperatures barely above those attained in the
current Martian environment. Examples include organic material as well
as reactive minerals that might be common (e.g., sulfates, chlorides,
and clays) yet whose stability could be compromised even at modest
temperatures (\<20°C). Liquid water or ice also might be present in
samples, either interstitially or sorbed onto mineral surfaces.
Accordingly, the temperatures experienced by samples during collection
and return to Earth would be a critical issue. In order to maintain
sample integrity, returned samples ideally should be kept as close as
possible to the ambient temperature (and atmospheric) conditions of the
location where they were collected. However the ND-SAG recognizes that
if this were set as a mission requirement, it might pose a major
technological challenge that may not be achievable within cost
constraints. If sample integrity were seriously affected by temperature
excursions, then the next best option would be to monitor the
temperature history closely and also ensure that samples are fully
encapsulated so that all components would be retained. Under these
conditions, any chemical reactions that may take place during transport
to Earth conceivably could be evaluated and reconstructed.

[]{#__RefHeading___Toc191123504 .anchor}Table 9 Effect of Maximum Sample
Temperature on the Ability to Achieve the Candidate Science Objectives.

![](media/image9.pct)

Elevated temperatures could compromise the integrity of organic
compounds (see MacPherson et al. 2005 for a good summary table). Even at
only --5°C, certain organic compounds are mobilized, and some organic
compounds decompose at \>-20°C. At temperatures of +50°C, significant
decomposition takes place, and if samples remain at this temperature for
more than about three hours, science objectives related to life goals
could be seriously compromised.

Most inorganic materials should remain suitable for allowing primary
scientific objectives to be achieved even if these materials experience
temperatures as high as +20°C. At higher temperatures, such as +50°C,
some materials (e.g., regolith, dust, clays) might deteriorate and
potentially lose key scientific information. Although the kinetics of
many reactions is poorly known and some metastable phases may persist
well outside their nominal stability ranges, sulfate minerals are very
likely to present a special challenge. For example, the hydration states
of magnesium and iron sulfates are sensitive to temperature and relative
humidity and changes (dehydration and/or melting) might commence at
temperatures as low as --2°C. Dehydration and melting should be expected
if temperatures reach 20°C. These changes have the potential to
seriously influence both the chemical and physical state of the samples.
For example, dehydration of MgSO~4~•*n*H~2~O from *n*=11 to *n*=1 would
result in nearly a factor of four loss of mineral volume that could lead
to physical disaggregation of weakly cemented samples. Release of water
could result in further chemical reactions, such as dissolution of
highly soluble minerals (e.g., chlorides), leaching of weakly held ions
(e.g., clays) or significant lowering of pH through Fe^3+^ hydrolysis.
Finally, water ice may be stable within cm of the Mars surface (e.g.
Mellon et al. 2004) therefore it could occur in a regolith sample or
drill core. Refrigeration and temperature monitoring would allow an
accurate assessment of whether any reaction between this water and the
surrounding sulfates or soluble minerals has taken place during sample
return.

The ND-SAG has confidence that the MSR scientific objectives that depend
upon mineral compositions could be addressed if samples were kept below
about --10°C. For preservation of water, it would be preferable to hold
the samples below about -20°C (MEPAG SR-SAG, 2006). There is less
confidence, but it is likely, that most objectives would be met for
samples that are kept below about +20°C. If samples were allowed to
reach +50°C for greater than about 3 hours, the damage that ensues would
seriously degrade the scientific value of the samples. It is very
possible that samples containing Mg- and Fe-sulfates would be altered
substantially even if temperatures approach only 20°C, but these effects
could be mitigated if samples are encapsulated and their temperature
history monitored. Monitoring sample temperature during transport to
Earth would help determine any post-sampling melting or
recrystallization. For example, MgSO~4~ .11H~2~O, which was identified
at the Opportunity site and subsequently found on Earth (Peterson et al.
2007), is expected to dehydrate at 2°C. Maintaining a low temperature
would inhibit this mineralogical transformation.

Far worse for the science value of the samples than heating to 20-50°C
would be heating to a level sufficient for biological sterilization. It
is a common misconception that heat sterilization of samples would
damage them relative only to astrobiological (MEPAG Goal I) goals (e.g.,
Steele, et al., 2007). Heat sterilization would impact the samples in
several ways, some relevant to the other objectives of the mission.

## 

[]{#__RefHeading___Toc191123531 .anchor}Diversity of the returned
collectionThe diversity of the suites of returned samples must be
commensurate with the diversity of rocks and regolith encountered during
the mission. Sample suites that capture this diversity would empower the
maximum possible number of investigations and thereby effectively
address major questions such as how geologic, climatic, and potential
biologic processes have changed through time. The Viking landers and the
Pathfinder and Mars Exploration Rovers have demonstrated that the
Martian surface is lithologically diverse. By returning samples to
state-of-the-art terrestrial laboratories, more subtle mineralogical and
compositional variations would be likely to emerge. Because the size of
a sample suite reflects the number of samples necessary to characterize
a given site, the set of suites that accurately represent the diversity
of each key rock type at a site would constitute the minimum quantity of
sample that would be required.

Changes in geologic, climatic, and potential biologic processes could
only be addressed by examining multiple samples that represent different
intervals of time. For example, in order to understand the origin and
evolution of fluids responsible for sulfate deposition, numerous
sulfate-bearing samples would be required that record evolution of any
fluids through time. Likewise, understanding a siliciclastic
depositional environment would require determining how the rock sequence
changed through time; thus a stratigraphic sequence must be sampled.
Finally, understanding the evolution of the Martian interior or an
individual volcanic edifice would require sampling igneous rocks
produced at different times. The lithologic diversity of the sample
collection must be maximized to ensure that a record of any temporal
mineralogical, geochemical, and organic chemical variations has been
captured in the returned collection.

The lithologic, compositional, and temporal diversity of the returned
sample collection would be the single most important factor controlling
the range of investigations that could be addressed using the samples.
For example, many investigations involving habitability, the carbon
cycle, the search for life, and the role of water on the Martian surface
would require rocks containing hydrous phases. Some aspects of these
investigations, as well as investigations regarding the evolution of the
atmosphere, climate, surface, and interior of Mars, could only be
addressed with siliciclastic sediments, igneous rocks, and regolith.
Consequently, a primary exploration objective of MSR should be to
maximize scientific yield by ensuring that the sample collection has the
largest possible lithologic diversity. This essential objective should
substantially influence both the selection of landing sites and the
development of rover operation protocols. For example, mission
strategies to acquire samples by visiting multiple sites are more
effective at capturing a greater diversity of samples.

In sum, the necessary diversity of samples implies more than one sample
return mission (more than one site, and/or more than one mission).
Although this is an assumption made up front by this study, it is worth
reinforcing the point (see also section VII).

## 

[]{#__RefHeading___Toc191123532 .anchor}Surface OperationsIn order to
achieve the MSR scientific objectives and access the kinds of sites of
greatest current interest, a high priority would be to deploy a
spacecraft that has significant horizontal range and could navigate
rough terrain. Although the current orbital imagery provides excellent
context and mineralogical information in order to identify high priority
landing sites, experience from the Mars Exploration Rovers has shown
that the diversity of potential samples that exists at the size scale of
a rover must be analyzed *in-situ*. The MSR lander/rover must have
instrumentation that could interpret the diversity of geologic materials
and help to select the highest priority samples for return (see section
IV.D). Color imagery, remote spectroscopic observations and contact
geochemical/mineralogical analyses constitute the minimum set of
techniques would be needed to optimize sample selection. The duration of
surface operations would also influence the quality of the sample
collection. ND-SAG expects that a minimum of 6-12 months of surface
operation would be required in order to reconnoiter a site and identify,
characterize and collect a set of samples that captures its
compositional diversity. To place this in context, the Opportunity rover
did not complete the stratigraphic characterization in Endurance crater
until Sol 315 (Squyres and Knoll, 2005) and Spirit did not identify
significant indicators of aqueous processes until it reached the
Columbia Hills (roughly Sol 180; Arvidson et al., 2006). Sending MSR to
a previously visited site (either of the two MER sites, the MSL or
ExoMars site, or potential future sites) might substantially reduce the
time needed for reconnaissance, but revisiting a site might also
compromise samples intended for organic analyses by increasing the risk
of terrestrial contamination.

## 

[]{#__RefHeading___Toc191123533 .anchor}Documented Sample OrientationThe
scientific value of the returned collection could be improved if sample
orientation is documented for at least some of the samples. The primary
use for this sample attribute would be in paleomagnetic studies (see
Appendix II; Investigations IIIA-10 and IIIB-2), but it may also be
useful in interpreting paleoflow directions for sedimentary rock
samples.  The scientific need could be met if the sample orientation in
known to within \~10 degrees.

The orientation measurements could in principle be determined, through a
combination of telemetry and imagery (the same technique is used on MER,
where orientation precision is determined to within a few degrees). 
Telemetry includes overall rover orientation from the IMU and joint
angles from the arm.  Imagery includes the documentation images of the
science target as well as operational imagery showing the arm in place
and the position of the instruments (and corer) as the samples are
obtained.  This information is already required for sample documentation
and safety monitoring of arm operations, therefore determining the
orientation should not add any additional requirements on the system.
Finally, we need to know the rotational orientation of the core sample.
This may be available for indurated samples by comparing images of the
surface with MI images taken before drilling.  Although not all samples
will preserve the top after drilling, enough may do so to be sufficient
to meet the science goals of the mission. Of course alternative methods
for marking the rotational orientation might be superior and should be
sought.

## 

[]{#__RefHeading___Toc191123534 .anchor}Planning Considerations
Involving the MSL/ExoMars CachesA decision was made in mid-2007 to add a
simple caching capability to the 2009 MSL mission. As of this writing, a
similar cache is under consideration for ExoMars. This capability is
part of a larger strategy to utilize pre-MSR landed missions to enhance
the value of sample return. It is intended that the recovery of the MSL
cache will be an option for MSR, rather than a requirement. The decision
would be made several years from now by future science teams and other
decision-makers.

[The MSL cache design]{.underline}.

The MSL cache is designed to accept 0.5--1.5 cm rock samples provided by
MSL\'s soil scoop, collected over 5--10 separate caching events (Karcz
et al., 2007). The cache will have mesh sides to allow fines to filter
out, leaving behind rocks. The strategy for employing the scoop to
acquire either individual targeted rocks, or rock-bearing regolith would
depend on further experience with prototype scoops (note that the volume
of the scoop is roughly half the volume of the cache). The empty cache
is specified to have a mass less than 52 g. However, the mass of the
latest revision of the design (as estimated by the CAD software) is 29 g
(Karcz, writ. comm., 01-07-08). A draft specification (as of this
writing) is for the mass of the full container to be 200 g or less.
Because the mass of the contents will be uncertain, it is likely that
the science team will fill it to somewhat less than capacity\--to, say,
180 g instead of 200 g.

The cache and rover will not be sterilized, but any organisms on the MSL
cache and rover, and in MSL\'s assembly, test, and launch environments
will be inventoried using genetic methods. The MSL Project Science Group
will direct caching operations and sample selection. The current
strategy is to collect samples representative of the common rock and
mineral types encountered by MSL during its traverse, rather than
specifically targeting "unusual" finds.

[Potential consequences of the MSL cache for MSR.]{.underline}

The ND-SAG evaluated several major impacts that the MSL cache might have
on the design of the first MSR mission. The following three sets of
questions and answers summarize the outcome of these deliberations.
These answers draw substantially from the findings of Steele et al.
(2008).

**1. If a cache prepared by MSL (or ExoMars, or any other future
mission) is recovered, would MSR necessarily acquire additional samples
in order to achieve its key scientific objectives, or would the samples
in the cache be sufficient? If additional samples are required, then the
MSR spacecraft must have an independent sample acquisition capability.**

[Discussion]{.underline}. The cache's samples have the advantage that
they might be collected from a wider geographic area than is possible by
MSR. This is particularly true for the MSL rover, which has a nominal
mobility range that might be an order of magnitude higher than that of
an MSR rover. For whatever reason, MSL might discover and collect unique
samples that the MSR could not collect on its own. However the MSR
mission might not be able to retrieve the MSL cache. For example, the
MSR spacecraft might land too far away, the MSL rover might end its
mission in an inaccessible location, or the cache itself might be in a
state that would render its irretrievable.

MSL's cached samples will be limited to small rocks that its scoop could
retrieve from the Martian surface. Isolated small rocks might be heavily
weathered. Several of the MSR objectives require unaltered samples from
rock interiors.

The present design of the MSL sample collection and caching system will
not permit the assembly and packaging of all of the samples necessary to
address the scientific objectives proposed for MSR in this report. The
cached samples will be neither labeled nor separated from each other;
therefore the identity of each sample and therefore the information
about its environmental context might be obscured during caching of the
samples. Loss of context data would significantly reduce the science
return, particularly for the high priority life-related objectives.
Because the cache samples are not to be individually encapsulated, any
mechanical disruption during transportation back to Earth might
intimately mix the samples and contribute further to the loss of their
individual identities.

The standards for organic contamination and planetary protection for the
MSL and MSR missions would probably be different (as of this writing,
the MSL contamination thresholds are known, but those for MSR are not).
The MSL sampling system will not be sterilized. If the MSL cache harbors
biological material whose origin could not be determined (Is it from
Mars? Or is it Earthly contamination?), planetary protection protocols
will require that the returned cache samples be sterilized. Stringent
sterilization procedures would severely degrade the scientific value of
these samples for several of the MSR science objectives.

Finally the MSR mission should be able to respond to any discoveries
whose follow-up would require samples other than those in the MSL cache.

Accordingly, the ND-SAG found that the MSR landed spacecraft should have
the capability to collect at least some of the samples to be returned by
itself.

**2. If the MSR spacecraft must have sample acquisition capability, does
the specific nature of that capability depend on whether or not it would
attempt to recover a cache?**

[Discussion]{.underline}. The MSL cache could substantially improve the
MSR return if certain scenarios occur. For example, if the time
available for MSR surface operations becomes severely limited, it might
be able to collect a relatively small number of samples on its own and
the MSL cache would become especially important.

According to current plans, the mass and volume of the MSL or ExoMars
caches are estimated to occupy about one-third of the proposed returned
sample capacity. MSR therefore must acquire either two-thirds or all of
the returned samples. As discussed above, the MSR spacecraft must have
the capability to collect all of the sample types of interest.

Therefore the design of the sample acquisition system of MSR would be
independent of the decision to recover either the MSL or the ExoMars
caches. Note that a key consideration in this analysis is whether a
given kind of sample discovered by MSL would be sufficiently useful in
an Earth-based laboratory if stored in the cache, or whether it would be
preferable to have MSR recollect it.

**3. If MSR returns to a previously visited site (e.g., those of MSL,
ExoMars, MER, other?) where the geologic** **terrain has been
characterized previously to some extent, would the landed
instrumentation required for MSR differ from that required in order to
visit a new site?**

[Discussion]{.underline}. MSL will carry a highly capable in-situ
laboratory that will be able to characterize the samples and their
geologic context in many ways and with superior precision and accuracy.
MSL has 10 instruments, including highly capable chemical and
mineralogic detectors. It is unlikely that MSR would carry an instrument
package of this quality. Therefore the geologic context of the MSL site
will be significantly better understood than any other site that the MSR
rover might visit. This same argument will also apply to the site
visited by ExoMars, and to a lesser extent to the two MER sites
(Meridiani and Gusev Crater).

However there are differences in perspective within the ND-SAG regarding
how closely the MSR rover would have to follow the footsteps of a
previous rover in order to take advantage of that previously acquired
information. Opinions range from the view that sampling the same
stratigraphic bed would be adequate to the view that the same drill hole
must be re-sampled. The further the MSR rover departs from the tracks
left by the previous rover, the more important it would be for MSR to
have its own instruments to guide its sampling operations. In addition,
the presence of instruments on MSR would allow the mission to follow up
on unexpected discoveries and/or to pursue scientific questions that
were not addressed by the previous mission.

There is also a concern about contamination should MSR re-visit sites. 
The MSL contact instruments and tools would be decontaminated to a level
that allows for the confident detection of Martian organics if present,
but this is not true of MER. Does this mean that we would need to avoid
sampling directly any location previously sampled by a MER or MSL?  If
so, returning to a MER site may not provide the benefit of a reduced
payload because if we want to sample \"sister\" materials rather than
the exact same materials, we might need a fairly sophisticated
instrument payload rather than a minimal one. This topic needs further
discussion by the community.

[]{#__RefHeading___Toc191123505 .anchor}Table 10 Relationship of the MSL
cache to planning for MSR.

![](media/image10.pct)*Notes on Table 10. For MSL Objective 8 (Risks to
Human Explorers), there is a need to acquire both regolith and dust
samples. Because samples in the MSL cache will be exposed to the*
*Martian environment during the period of time between MSL and MSR, the
samples will be covered with dust. Although this dust could be extracted
after return to Earth, the amount would be very little. For MSL
Objective 9 (Oxidation), the degree of relevancy of the cached samples
depends largely on the design (including depth range) of the ExoMars
drilling system, and the capability of ExoMars to cache those samples.*

[Expected contribution of MSL cache samples to the scientific objectives
for MSR]{.underline}

Steele et al. (2007) recently assessed the expected scientific value of
the MSL cache. Their results are summarized with respect to the 11
candidate scientific objectives for MSR in Table 10. For Objectives 7
(Regolith), 10 (Gas Chemistry), and 11 (Polar), the MSL cache will not
make any contribution because it will not have the capability to acquire
and store regolith, atmosphere, and ice samples.

For the rest of the MSR scientific objectives, the contribution of the
cached samples would likely be 'minimal' to 'some', depending on what
MSL encounters and the nature of the samples selected for caching. The
priorities for additional sampling by MSR reflect the comparison of the
objectives for the MSL cache and the MSR mission and are summarized in
Table 10.

In its discussions both internally and externally, ND-SAG has observed
that the two main sectors of the Mars science community that would be
able to make the most use of returned samples, namely astrobiologists
and geologists, tend to view the strengths and limitations of the MSL
cache differently. For our astrobiology objectives, the limitations are
a major concern, whereas for at least some geologists, the strengths are
more important. In order for MSR to maximize its scientific return, the
samples need to serve the needs of BOTH astrobiology and geology, and we
encourage all sectors of the community to be sensitive to other points
of view.

In summary, for each of the 11 candidate scientific objectives for MSR,
ND-SAG concludes that the expected contribution from the cached samples
alone would not be sufficient to achieve the main scientific objectives
proposed, and that additional sample acquisition/packaging by MSR would
greatly enhance the science return. The MSL cache has the potential to
increase the diversity of the samples; however it would imply a larger
complexity for MSR in operations and possibly a larger mobility.

## 

[]{#__RefHeading___Toc191123535 .anchor}Planetary ProtectionThe purpose
of planetary protection is to prevent forward contamination of other
solar system bodies (in this case, Mars) by Earth organisms and to
prevent harmful contamination of the Earth's biosphere by
extraterrestrial organisms. The requirements associated with planetary
protection are a critically important aspect of planning MSR. Although
there are many planetary protection issues related to MSR, ND-SAG
identified two topics of particular significance to the science value of
MSR: 1) The relationship of MSR to "special regions" and 2) The effects
of possible heat sterilization of the sample.

In this area, we need to be especially careful to distinguish our
discussion of MSR in general from planning for the first MSR.

**1. How important is it to hold open the option of sending MSR to a
planetary protection \"special region\"?**

In the past few years a new category of planetary protection has been
defined and which is of particular interest to astrobiologists and the
search for modern life. These are "special regions." Special regions
were defined in order to provide extra protection to Martian
environments where terrestrial microbes could propagate (COSPAR, 2002;
2005). In simple terms, special regions have been interpreted to be
environments with recent liquid water, and this has been quantitatively
refined as locations where two environmental conditions are
simultaneously met: the temperature is greater than -20°C, and the
activity of water is greater than 0.5 (MEPAG SR-SAG, 2006; COSPAR, in
prep.). Such environments, if they could be identified, would be of very
attractive targets for MSR because of the potential for extant
indigenous Martian life.

Accessing and sampling special regions is permitted by planetary
protection policy. Doing so would require the sterilization of the
spacecraft components that penetrate the special region. For missions
that access a special region by means of roving, reaching, or drilling,
the subsystems that penetrate the special region would need to be
sterilized. For missions that land within a special region, or missions
where a special region is present within the landing error ellipse, the
entire landed system would need to be sterilized because of the
potential of a spacecraft failure and break-up during EDL. In either
case, MSR development would be significantly more complex in an
engineering sense, thus increasing mission cost and risk. 

At the time of this writing, no Martian environment, either surface or
subsurface, has been identified that is known to meet the technical
thresholds for a special region. However, there are several kinds of
environments that exist on Mars for which it there is ambiguity as to
whether they meet the threshold conditions for "special region" or not
(e.g. mid-latitude gullies, pasted-on terrain). In the latter case,
since they cannot be shown to be "not-special", and for the purpose of
planetary protection, which requires conservative approaches, they are
treated as if they are "special". In addition, MEPAG SR-SAG (2006)
pointed out several kinds of geologic environments that if discovered by
future researchers could qualify as special (active volcanoes,
hydrothermal vents, large very young large craters).

For the purpose of planning MSR, it is important to recognize the
difference between the attitude of planetary protection towards an
environment with ambiguity (if there is a question, be conservative and
treat as if special), and that of the science community (we need a high
degree of confidence that the samples we want would be at the site
selected---MSR is not the right choice of a mission to be probing sites
that have major uncertainty).

[Discussion---planning for the first MSR]{.underline}. The reality is
that we cannot at present credibly propose that the objective of the
first MSR be to find the extant Martian life and return it to Earth---we
don't know where to go or what to sample. We have no information on the
environmental habitability factors for unknown Martian life forms. Our
best guess is that the most favorable environment would be one with
liquid water (which would qualify as a special region), but we have not
yet made that discovery. For these reasons, proposed Scientific
Objective #2 of this report is phrased "assess the evidence for
pre-biotic processes, past life, and/or extant life". The specific
strategy for how to achieve this is left up to future landing site
selection committees and other such planning teams. Note that since
pre-biotic chemistry and the possibility of past life can be evaluated
without the need to go to a special region, special region access is not
required to achieve this objective. The objective could be alternatively
be achieved through the study of ancient environments and their geologic
products (e.g., sedimentary, igneous, and hydrothermal rocks), for which
knowledge of their distribution is much more confidently known.

However, retaining the option to sample a special region with the first
MSR would be valuable scientifically in the sense that it may allow us
to respond to the discovery of liquid water within the next 5-10 years.
Thus, for the first MSR mission, this question boils down to balancing
the probability of making such a discovery against the increased cost of
mission development (the development cost would be incurred whether the
mission is eventually sent to a special region or not). This trade is
best evaluated by a joint science-engineering team that could
specifically evaluate both the cost and the benefit.

ND-SAG additionally observes that MEPAG SR-SAG (2006) presented very
convincing arguments that for thermodynamic reasons, the most
prospective part of Mars for near-surface modern liquid water is the
latitude band 30-60° (both north and south latitude), and that it is
almost impossible for liquid water to exist equatorward of 30° latitude.
If MSR adopts equatorial landing site restrictions for EDL reasons,
there would be little reason to believe that special region access
capability could actually be used.

Note that whether MSR would or would not be sent to a special region is
unrelated to whether the returned samples would be evaluated for extant
Martian life---they assuredly would be, even if they do not come from
special regions. 

**2. What would be the effect on the science value of the samples if
they are heat sterilized prior to Earth return?**

[Discussion---planning for the first MSR]{.underline}. Since we have no
information about Martian life, beyond a reasonable hypothesis that it
is most likely to be carbon-based, the only way to be confident of
destroying it is to destroy the chemicals on which that life depends
(Nealson et al., 1997).  This has been interpreted to involve either
heating the entire sample to 500C (half a second at the most protected
location is presumed to be adequate), or some combination of high
temperature and hard radiation (Nealson et al. 1997; Conley, writ.
comm., 2008).  Treating the samples this harshly would have severe
negative impacts on the scientific usefulness of the returned material:

a.  
b.  
c.  
d.  

Destroy or alter organic material within the sample, including
components such as amino acids, polycyclic aromatic hydrocarbons, and
paraffins, needed to evaluate hypotheses involving prebiotic chemistry,
past life, and modern life. Destroy or alter many hydrous minerals such
as clays, sulfates, and hydroxides that are essential to interpreting
the aqueous history of Mars.For samples that are not encapsulated,
components released from one sample could react with other samples,
causing the samples to no longer be representative of the Martian
environment.Adversely affect studies on possible (unknown) oxidant
phases in regolith samples.In addition, from a planetary protection
standpoint there is no rationale to attempt sterilization of samples
prior to Earth return.  Since no method for the sterilization of
putative Martian life has been validated, it would be very difficult to
justify allowing the return of uncontained samples regardless of how
they had been treated prior to Earth entry (Conley, writ. comm., 2008). 
ND-SAG concludes that heat sterilization of the samples would entail
major negative consequences without any real benefit.

# 

[]{#__RefHeading___Toc191123536 .anchor}Program Context, and Planning
for the First MSR MSR would not be a one-time stand-alone mission.
During the course of deliberations by ND-SAG it became evident that
relationships must be more clearly defined between MSR, the Mars
Exploration Program (MEP), and the eventual human exploration of Mars.

The MEP lays out a logical progression of missions that build upon the
past and lead to the future. In that sense, the recent, current, and
planned missions have already and would continue to contribute to a
superior first MSR mission (see Section IV.A). We thus believe that a
first MSR mission in the next decade would be far better scientifically
than any MSR mission that might have been implemented earlier. This
validates NASA's foresight in establishing the MEP many years ago and
its belief that Mars holds a special place in planetary exploration. The
ND-SAG anticipates that such a productive return-on-investment would
continue after the first MSR mission: there is no doubt that the
analyses of the returned samples would significantly alter our
understanding of Mars and greatly enhance our interpretation of current
and future remote sensing data. This conclusion has been "validated" by
the Apollo program in which the results from the Apollo-11 returned
samples directly and rapidly impacted subsequent Apollo missions and led
to the establishment of many of the science objectives for the current
spate of lunar robotic missions.

For the first MSR mission, we need to balance the need to keep the
mission from becoming overly complex in an engineering sense, while at
the same time retaining the essential attributes that contribute to the
scientific value. As input to these trades, the ND-SAG team has
summarized in Table 11 the various attributes discussed in this report
that would improve the science value of MSR, along with a preliminary
assessment of the impact of these attributes on mission engineering.
Since there are legitimate differences of opinion within the science
community on the priority of these attributes, and the planning for a
possible MSR is still in its early stages, rather than try to reach
consensus on a single set of priorities, three example priority
positions are shown in the columns on the right. This illustrates both
the commonalities and the differences in how different sectors of the
science community value these attributes.

The question naturally arises as to what follows MSR in the MEP. First,
we do not consider MSR to be a single-mission event. The great diversity
of Mars makes it probable that not all MSR objectives could be achieved
at one sample site. Landing site engineering constraints for the first
MSR mission prohibit going to certain terrains, such as polar regions
and rough topography (e.g., the gullies of "uncertain special regions"
or "special regions"). The data gleaned from the first MSR mission would
likely stimulate the desire to conduct additional MSR missions.

There is an aspect of a "second MSR mission" that merits our attention,
to wit: the MEP may decide, for reasons of [program]{.underline} risk
reduction, to advocate replicating the riskier elements of the mission,
e.g. landing and ascent systems. If such appears prudent and affordable,
we could today make a convincing case that returning samples from two
substantially different sites on Mars would be eminently prudent. The
living example of this risk-reduction philosophy is the MER mission, for
which the NASA administrator chose to send two landers.

The ND-SAG emphasizes that, however important, the first MSR would not
be the finale of a science-driven MEP. We know now that other mission
types need to be considered for opportunities immediately following the
first MSR. There are already high priority proposed and studied mission
concepts that are relatively independent of MSR results (e.g., network
missions, orbital science) and that could be implemented immediately
after the first MSR. Indeed, it is virtually inevitable that the results
of the first MSR would lead to new proposals for non-MSR orbital and
surface science missions.

[]{#__RefHeading___Toc191123506 .anchor}Table 11 Science priority of
attributes of the first MSR.

The MSR mission would have a significant relationship to eventual human
exploration. As shown both in the MEPAG Goals and in this study,
information gleaned from the returned samples would be directly related
both to the health and well being of astronauts on Mars and to reliable
operations on the Martian surface. There is an associated indirect yet
important aspect: the detailed knowledge obtained from the returned
sample would inevitably inform what science astronauts would do at Mars
and how they would do it. For these reasons an MSR mission probably
would be required at the landing site eventually selected for human
exploration (which may or may not be a prior MSR site). Again we refer
to the Apollo missions in which post Apollo-11 mission science was
altered in response to findings from returned samples. Lastly, there
would be the "proof-of-concept" element of MSR in which the
demonstration of the roundtrip to Mars with successful Earth-return
bolsters public understanding and conviction that it is indeed feasible
for humans to eventually make that sojourn.

# 

[]{#__RefHeading___Toc191123537 .anchor}SUMMARY OF FINDINGS AND
RECOMMENDED FOLLOW-UP STUDIES [Editorial Comment: This section needs
final revision after the review process.]{.mark}

Additional discussion is recommended in the following areas.

1.  

2.  

3.  

4.  

5.  

6.  

7.  

8.  

9.  

10. [MSR landing site selection process and timing]{.underline}. How
    would the specific candidate landing sites for MSR be identified and
    screened for safety? Would it be prudent to use the instruments on
    MRO for this purpose while the orbiter is still healthy? We need to
    take into consideration the expected availability of orbital
    instruments during the second decade.[Contamination
    limits---Organic]{.underline}. Two MEPAG teams have considered this
    in detail within the past five years: the Organic Contamination SSG
    (Mahaffy et al., 2003), and the MSR2-SSG (which produced only a
    draft report). The latter report concluded that "while OCSSG
    specified contamination levels for organic molecules that are
    adequate for a subset of the samples where organic analysis is not
    the primary objective, thresholds that are lower by a factor of 4 or
    more are desired for an isolated subset of the samples, such as
    cores from sedimentary deposits or selected rocks, where organic
    analysis would be a primary investigation. Although modern
    instrumentation may be able to detect much lower levels of organics,
    achieving a significantly lower threshold may be impractical as may
    the realization of lower organic levels in blanks used during the
    sample analysis. The Apollo experience suggests that these
    thresholds could be realized. These arguments should be reconsidered
    in light of experience and results from 2007-PHX and 2009-MSL. \[DJD
    comment: where should the second quotes punctuation (") be placed to
    close the " located in the second sentence of this
    paragraph?\][Contamination limits---Inorganic]{.underline}. The
    2004-05 MEPAG-sponsored study considered the topic of inorganic
    contamination thresholds for MSR in some detail (Section IX of
    MacPherson et al. (2005). They proposed that a good guideline for
    acceptable contamination levels for major and minor elements is 0.1
    percent of the concentrations in SNC meteorites. These arguments
    should be reconsidered in light of experience and results from
    2007-PHX and 2009-MSL.[Depth of subsurface access]{.underline}. A
    major open question in Mars science is the nature of the
    relationship between the inferred oxidizing surface zone, and the
    inferred reduced subsurface zone. What is the depth scale of the
    effect of oxidation in the near subsurface? This scale is presumably
    dependent on permeability, so it is likely to be different in rocks
    than in regolith. Although we have little data to constrain this, we
    need to make some decisions on the scale of the subsurface access
    hardware to be included on MSR.[For core samples: length vs.
    diameter]{.underline}. Although this report concludes both that rock
    sample acquisition by a mini-corer, and that rock samples must be
    larger than about 5 grams, would be very important, the ND-SAG team
    did not attempt to evaluate the optimal combination of mini-core
    length and diameter.[Sampling splitting strategy required for PP in
    the SRF]{.underline}. In order to plan for acquiring samples of the
    correct size, we must understand how the different types of samples
    (e.g., igneous or sedimentary rocks, regolith, etc.) would be split
    within the Sample Receiving Facility, and how much sample material
    would be needed for destructive hazard assessment testing.[Landing
    site targeting precision and its relationship to minimum roving
    distance capability and time on the surface]{.underline}.
    TBD.[Instruments/observations---including relationship to
    MSL/ExoMars cache]{.underline}. TBD.[Number of samples and overall
    mass]{.underline}. TBD[Preparation of a Design Reference
    Mission]{.underline}. We need to prepare a Design Reference Mission
    that would summarize how we would collect samples and characterize
    the site, address the key questions that this exploration was
    designed to answer, and respond to the new discoveries.  We suggest
    that we do such a study for the Columbia Hills.  Such an analysis
    would tell us how much documentation we have to do to understand the
    context of a site, how much sample we have to take to characterize a
    specific type of rock (or process) in the Columbia Hills, and how
    far we have to go to \"fill the box\" for MSR, addressing the
    questions that we know to be important there. 

# 

[]{#__RefHeading___Toc191123538 .anchor}ACKNOWLEDGEMENTS In addition to
the 30 members of the ND-SAG team, the following additional scientists
contributed to the breadth of ideas in Appendix II:

MEPAG Goal I. Anderson, Marion (Monash U., Australia), Carr, Mike
(USGS-retired), Conrad, Pamela (JPL), Glavine, Danny (GSFC), Hoehler,
Tori (NASA/ARC), Jahnke, Linda (NASA/ARC), Mahaffy, Paul (GSFC),
Schaefer, Bruce (Monash U., Australia), Tomkins, Andy (Monash U.,
Australia), Zent, Aaron (ARC)

MEPAG Goal II. Bougher, Steve (Univ. Michigan), Byrne, Shane (Univ.
Arizona), Dahl-Jensen, Dorthe (Univ. of Copenhagen), Eiler, John
(Caltech), Engelund, Walt (LaRC), Farquahar, James (Univ. Maryland),
Fernandez-Remolar, David (CAB, Spain), Fishbaugh, Kate (Smithsonian),
Fisher, David (Geol. Surv. Canada), Heber, Veronika (Switzerland),
Hecht, Mike (JPL), Hurowitz, Joel (JPL), Hvidberg, Christine (Univ. of
Copenhagen), Jakosky, Bruce (Univ. Colorado), Levine, Joel (LaRC),
Manning, Rob(JPL), Marti, Kurt (U.C. San Diego), Tosca, Nick (Harvard
University)

MEPAG Goal III. Banerdt, Bruce (JPL), Barlow, Nadine (Northern Ariz.
Univ.), Clifford, Steve (LPI), Connerney, Jack (GSFC), Grimm, Bob
(SwRI), Kirschvink, Joe (Caltech), Leshin, Laurie (GSFC), Newsom,
Horton, (Univ. New Mexico), Weiss, Ben (MIT)

MEPAG Goal IV. McKay, David (JSC), Allen, Carl ((JSC), Jolliff, Brad
(Washington University), Carpenter, Paul (Washington University),
Eppler, Dean (JSC), James, John (JSC), Jones, Jeff (JSC), Kerschman,
Russ (NASA/ARC), Metzger, Phil (KSC)

Part of this work was carried out at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration. The contribution to this work
performed by Lars Borg was done under the auspices of the U.S. DOE by
Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
D. J. Des Marais and Lisa Pratt acknowledge support from the NASA
Astrobiology Institute.

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51. 167 -- 175

**APPENDIX 1 (ND-SAG CHARTER)**

**Science Issues and Priorities for a Next Decade MSR**

**Science Analysis Group (ND-SAG)**

[Introduction]{.underline}

On July 10, 2007, Dr. Alan Stern, AA-SMD, described to the participants
in the 7^th^ International Conference on Mars his vision of achieving
MSR no later than the 2020 launch opportunity. He requested that the
details of this vision be analyzed over approximately the next year for
financial attributes, for scientific options/issues/concerns, and for
technology development planning/budgeting.

MEPAG has been asked to contribute to this effort by preparing an
analysis of the science components of MSR and its programmatic context.
To this end, MEPAG hereby charters the Next Decade MSR Science Analysis
Group (NDMSR-SAG). The output of this team will constitute input to a
Mars program architecture trade analysis.\
 \
[Starting assumptions]{.underline}

1.  Assume that the sample return mission would begin in either 2018 or
    2020.

2.  Assume that MSL will launch in 2009, and will prepare a simple cache
    of samples that is recoverable by the MSR rover. Assume that ExoMars
    may carry a similar cache.

3.  Assume that a post-MSL sample acquisition functionality would be
    associated with MSR. This functionality may either be landed at the
    same time as the sample return element of MSR, or it may be
    separated into a precursor mission.

4.  Assume a stable program budget, about \$625M/year, growing at
    2%/year.

Requested Tasks

1.  Evaluate the science priorities associated with the design of the
    sample collection to be returned by a next decade MSR mission.

    a.  [Returned sample characteristics]{.underline}. Based on the 2006
        version of the MEPAG Goals Document, which scientific objectives
        could be achieved/supported by sample return, and for each
        objective identified, what kind of samples would be necessary to
        answer the questions that have been posed?

        i.  Estimated number of samples

        ii. Physical condition of the samples

        iii. Contamination limits

             -   Earth-sourced organic contamination

             -   Inorganic contamination by sampling hardware and/or
                 sample containers

             -   Cross contamination between Martian samples

             -   Contamination by Martian airborne dust

        iv. Environmental controls needed for storage on the surface and
            during return to Earth

    b.  [Samples acquirable at a single operational site]{.underline}.
        Assuming that it is not possible to acquire all of the samples
        of interest at one landed operational site, prepare models for
        different kinds of geologic terrain showing how large a fraction
        of the samples of interest could reasonably be acquired at each,
        and by derivation, the kinds of scientific objectives that would
        be realistically achievable in a single sample return mission.

2.  What are the dependencies of the achievable scientific objectives on
    the following:

    a.  The sample acquisition functionality of the post-MSL
        MSR-affiliated sample acquisition functionality?

    b.  The instrument complement of the post-MSL MSR-affiliated sample
        acquisition functionality to provide information to support
        sample collection decisions consider ideal and minimal
        instrumentation sets.

    c.  Mobility and lifetime of surface operations for the post-MSL
        MSR-affiliated sample acquisition functionality

3.  Analyze what critical Mars science could be accomplished in
    conjunction with and complementing MSR.

4.  In planning Mars Sample Return to launch in 2020, it is expected
    that at least one launch opportunity would need to be skipped for
    the Mars Exploration Program to remain within its financial
    resources.  Given the launch opportunities of 2013 and 2016 (2018
    being skipped), what would be the first and second priorities for
    strategic missions in the next decade?

5.  As necessary, support MSR science planning as requested by the IMEWG
    MSR study.

Timing

The SAG should begin its discussions as soon as possible.

Results are requested in two phases, which will have different levels of
fidelity. An interim report is requested in early November, 2007, and a
draft report by Dec. 15, 2007.

Assume that this report will be discussed in detail by MEPAG at its next
full meeting, tentatively February 20-21, 2008, and that the final
report will consider feedback received in this exchange.

Report Format

The results of this SAG should be presented in the form of both a
Powerpoint presentation and a text white paper. Additional supporting
documents can be prepared as needed. After the report has been accepted,
it will be posted on a publicly accessible website.

The report may not contain any proprietary information or material that
is ITAR-sensitive.

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

David Beaty, Mars Exploration Directorate Chief Scientist, Mars Program
Office, JPL

Rich Zurek, Mars Exploration Program Chief Scientist, Mars Program
Office, JPL

Jack Mustard, Brown University, MEPAG Chair

July 24, 2007

**APPENDIX II Analysis of the use of returned** **Martian samples to
support the investigations described in the MEPAG Goals Document**

THIS APPENDIX IS APPROXIMATELY 100 PAGES IN LENGTH, AND IS PRESENTED AS
A SEPARATE DOCUMENT.

**APPENDIX III The first Mars Surface-Sample Return mission: revised
science considerations in light of the 2004 MER results**

Unpublished report, 62 pages in length.

[Authorship]{.underline}: Mars Sample Return Science Steering Group II
(Glenn MacPherson, Chair)

[Report Date]{.underline}: February 16, 2005

THIS APPENDIX IS PRESENTED AS A SEPARATE DOCUMENT.

**APPENDIX IV Science traceability from MEPAG Goals (2006 version) to
candidate MSR science objectives.**

The MEPAG science Investigations (left) are color coded into the flowing
4 areas:

1)  Gold -- Has been significantly addressed by missions to date, but
    MSR would still contribute

2)  Green -- High priority for MSR with significant MSR contribution

3)  Blue -- MSR would contribute

4)  Grey -- would not significantly addressed by MSR.

The candidate MSR science objectives (right) are color-coded purple for
high priority and pink for medium priority.

The arrows trace the linkage from the MEPAG science Objectives and
Investigations to the candidate MSR science objectives. Green areas
indicate linkages from MEPAG high priority Investigations for MSR to
candidate objectives. Blue arrows indicate lower priority MSR
contributions.

Note that the arrows originate both at the MEPAG Investigation and
Objective levels. Where they originate at the Investigation level, they
link the specific Investigation to the MSR candidate objective. Where
they originate at the MEPAG Objective level, they indicate that several
of the Investigations in that Objective address the MSR candidate
objective.

![](media/image13.wmf){width="6.281944444444444in"
height="8.302083333333334in"}

**APPENDIX V Comparison of the analysis of the** **Martian atmosphere by
MSL and in a returned sample on Earth.**

[Krypton and Xenon]{.underline}.  

The major questions to be addressed are the starting isotopic
compositions and to what extent those have been mass fractionated.  
Other questions involve the amounts of added nuclear components, which
include ^129^Xe from decay of extinct ^129^I, ^80^Kr and ^82^Kr from
neutron capture on Br, heavy Xe (e.g., ^136^Xe) from fission of extinct
^244^Pu, and possibly light Xe (e.g., ^124^Xe) from cosmic ray-induced
spallation.   Within our present knowledge, Kr isotopes appear
fractionated by \<7% and possibly much less across the 78-86 amu mass
range. Xe isotopes appear to be mass fractionation about 40% across the
^124^Xe-^136^Xe mass range, or \~4% per a.m.u.. In the analysis here, we
assume [each]{.underline} Xe and Kr isotopic ratio can be measured by
MSL to at least 1%, but possibly 0.1% on Earth. 

For Xe, MSL's 1% precision in ^124^Xe/^136^Xe or ^126^Xe/^136^Xe could
answer the question of the Xe starting composition. Also, a 1% precision
in ^129^Xe/^132^Xe would give the ^129^I decay component to satisfactory
precision. However, characterizing the smaller anticipated Xe isotopic
effects arising from GCR spallation and fission of Pu and U require a
precision better than 1%, and their characterization could yield better
data for the initial Xe composition than that likely to be determined by
MSL.

For Kr, the issue of starting composition may not be made clear by MSL
analyses, especially considering that mass 78 is often contaminated and
mass 80 and 82 will likely have an added component from neutron capture
on ^79^Br and ^81^Br. If we must determine the starting composition from
the ^83^Kr/^86^Kr ratio, and given this ratio only varies in Martian
meteorites by 2-3%, then a 1% precision on MSL measurement is not
sufficient to answer the question of Kr starting composition. Also,
knowledge of the exact neutron component of Kr is not obtained from a 1%
precision. Measuring these Kr isotopes on Earth to 0.1% precision would
give much more information. Thus a returned Xe sample is of at least
modest additional benefit, whereas a returned Kr sample is required to
answer the fundamental science questions.

[Argon.]{.underline}

There are two main science questions:  to what extent has atmospheric
loss fractionated ^36^Ar/^38^Ar, and how much ^40^Ar has been added from
decay of ^40^K. These are interacting data sets. We believe the current
^36^Ar/^38^Ar ratio is \~4, fractionated from a starting ratio of \~5.4
(Bogard, 1997). A 1% MSL precision in measuring this ratio (i.e., 4.00
±0.04) would be quite adequate for modeling Ar loss processes. Also, a
1% MSL precision in ^40^Ar/^36^Ar (e.g., 1800 ±18) would be quite
adequate in determining the amount of radiogenic ^40^Ar. Thus, there
would be [minimal]{.mark} rationale for a returned Ar sample. [(Don, you
raised this degree of relevance in the table up to modest---can you
please explain here?)]{.mark}

[Nitrogen.]{.underline}

The main science question is the degree of ^15^N/^14^N fractionation due
to atmospheric loss over time. Viking found this ratio to be enriched
over Earth by a factor of 1.62 ±0.16 (Nier and McElroy, 1977). For
modeling atmospheric loss processes, a 1% precision is quite adequate,
and little would be added from a returned sample.

[Neon.]{.underline}

The Martian neon composition is very poorly known, as is the mixing
concentration. Because of its low molecular weight, we expect Ne
isotopes to have been strongly fractionated during atmospheric loss. For
MSL, the analysis of ^20^Ne will have a problem with interference from
doubly ionized ^40^Ar. SAM will try to generate some information on
^21^Ne/^20^Ne and they will certainly take a shot at Ne isotope
measurement with the GC separation of Ar from Ne, but it is difficult to
get a good isotope measurement on a rapidly changing signal. There is
very strong rationale for a returned sample.

[Methane, volatile hydrocarbon, and sulfur gases.]{.underline}

In low concentrations, some trace gases probably could not be returned
to Earth without serious alteration. They are better measured on Mars.
However, this may not be true of methane, which is relatively inert at
ambient and lower temperatures, particularly if the gas sample is
isolated from solid Martian materials. Methane would be an important
measurement target for understanding regional to sample scale isotopic
systematics and differentiating abiogenic and biogenic hydrocarbon gas
sources (Sherwood Lollar, et al. 2002). Also important to distinguishing
models of methane formation would be the methane/ethane ratio. Neither
of these measurements will be possible with MSL. [Note: Max Coleman will
help with this before it is finalized.]{.mark}

[C and O in CO~2~ and H~2~O.]{.underline}

Viking reported ^13^C/^12^C and ^18^O/^16^O in CO~2~ to only 5%
precision (Nier and McElroy, 1997; Owen et al., 1977). There are two
different science questions. First, could we measure mass fractionation
due to atmospheric loss? To do so would require precisely measuring not
only the atmospheric isotopics, but those of condensed phases as well,
in order to know starting compositions. The second science goal relates
to isotopic fractionations that occur when these atmospheric gases
achieve chemical equilibria (including reactions) with condensed phases.
Again this would require precisely measuring not only the atmospheric
isotopics, but those of condensed phases. Many of these isotopic
fractionations occur at 0.1-1%, some much less. Thus to fully utilize
the science potential inherent in the O and C isotopics in atmospheric
CO~2~ probably would require their measurement to better than 0.1%. We
conclude that sample return of CO~2~ would be highly desirable to answer
both science questions posed.

As for H~2~O, it occurs in low concentrations in Mars' atmosphere and
would likely be altered during sample return. Thus, we conclude that
measuring O isotopic ratio in H~2~O would be better done on Mars.

[D/H.]{.underline}

A very elevated ratio in Mars\' atmosphere (about 4.5 times Earth\'s)
has been measured from Earth (Owen et al., 1988).  Controversy remains
over the D/H in Martian meteorites.  Leshin and co-workers have
suggested that it is enriched perhaps by a factor of two over Earth, but
Boctor and co-workers have argued it is more like Earth\'s (Leshin et
al., 1996; Boctor et al., 2006).  It would be very useful to get the D/H
in various hydrated samples. Also, H is known to be rapidly lost from
the atmosphere, and this loss over billions of years should produce D/H
fractionation even larger than observed in the atmosphere.  Thus, the
D/H probably varies over time and could be a measure of variations in
climate and volcanic degassing. There exists the potential to use the
D/H ratio in samples of different ages to examine climatic and degassing
episodes on Mars. It would be very useful to get the D/H in various
hydrated samples, which should be of greater value in addressing these
issues than a more precise determination of the present atmospheric D/H.