Science Priorities for Mars Sample Return


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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return, 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:

MEPAG Goal I. Anderson Science Priorities for Mars Sample Return, 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 Science Priorities for Mars Sample Return, 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 Science Priorities for Mars Sample Return), 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 Science Priorities for Mars Sample Return (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 Science Priorities for Mars Sample Return (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 Science Priorities for Mars Sample Return University), Eppler, Dean (JSC), James, John (JSC), Jones, Jeff (JSC), Kerschman, Russ (NASA/ARC), Metzger, Phil (KSC)


^ DRAFT-- OPEN FOR COMMENTS

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


Recommended Science Priorities for Mars Sample Return bibliographic citation:

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 Science Priorities for Mars Sample Return/reports/index.html.


Correspondence authors:

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 Science Priorities for Mars Sample Return OF CONTENTS

I. EXECUTIVE SUMMARY 1

II. INTRODUCTION 5

III. EVALUATION PROCESS 6

IV. SCIENTIFIC OBJECTIVES OF MSR 7

V. SAMPLES REQUIRED TO ACHIEVE THE SCIENTIFIC OBJECTIVES 14

^ VI. FACTORS THAT WOULD AFFECT THE SCIENTIFIC VALUE OF THE RETURNED Science Priorities for Mars Sample Return SAMPLES 27

VII. Program Context, and Planning for the First MSR 52

VIII. SUMMARY OF FINDINGS AND RECOMMENDED FOLLOW-UP STUDIES 54

IX. ACKNOWLEDGEMENTS 56

X. REFERENCES 57


^ LIST OF TABLES

Table 1: Scientific Objectives, ‘03/’05 MSR Science Priorities for Mars Sample Return, 2009 MSL, and 2013 ExoMars (order listed as in the originals) 8

Table 2 Planning aspects related to a returned gas sample. 23

Table 3 Summary of Sample Types Needed to Achieve Proposed Scientific Objectives. 27

Table 4 Subdivision history of Martian Science Priorities for Mars Sample Return meteorite QUE 94201 29

Table 5: Generic plan for mass allocation of individual rock samples 33

Table 6 Summary of number, type, and mass of returned samples. 36

Table 7 Science Priorities Related to the Acquisition System for Different Science Priorities for Mars Sample Return Sample Types. 38

Table 8 Rover-based Measurements to Guide Sample Selection. 40

Table 9 Effect of Maximum Sample Temperature on the Ability to Achieve the Candidate Science Objectives. 42

Table 10 Relationship of the MSL cache to Science Priorities for Mars Sample Return planning for MSR. 49

Table 11 Science priority of attributes of the first MSR. 53

Table 1: Scientific Objectives, ‘03/’05 MSR, 2009 MSL, and 2013 ExoMars (order listed as in the originals) 8

Table 2 Planning aspects related to a Science Priorities for Mars Sample Return returned gas sample. 23

Table 3 Summary of Sample Types Needed to Achieve Proposed Scientific Objectives. 27

Table 4 Subdivision history of Martian meteorite QUE 94201 29

Table 5: Generic plan for mass allocation of individual rock samples 33

Table 6 Summary of Science Priorities for Mars Sample Return number, type, and mass of returned samples. 36

Table 7 Science Priorities Related to the Acquisition System for Different Sample Types. 38

Table 8 Rover-based Measurements to Guide Sample Selection. 40

Table 9 Effect Science Priorities for Mars Sample Return of Maximum Sample Temperature on the Ability to Achieve the Candidate Science Objectives. 42

Table 10 Relationship of the MSL cache to planning for MSR. 49

Table 11 Science priority of attributes of the first MSR. 53
^ I.EXECUTIVE Science Priorities for Mars Sample Return SUMMARY
The return of Martian samples to Earth has long been recognized to be an essential component of a cycle of exploration that began with orbital reconnaissance and in situ Science Priorities for Mars Sample Return surface investigations. Major questions about life, climate and geology would require answers from state-of-the-art laboratories on Earth. Spacecraft instrumentation could not perform critical measurements such as precise radiometric age Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return. 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 Science Priorities for Mars Sample Return 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. Determine the chemical, mineralogical, and isotopic composition Science Priorities for Mars Sample Return of the crustal reservoirs of C, N, S and other elements with which they have interacted, and characterize C-, N-, and S-bearing phases down to submicron spatial scales in Science Priorities for Mars Sample Return order to document processes that could sustain habitable environments on Mars, both today and in the past.

  2. Assess the evidence for pre-biotic processes and/or life on Mars by characterizing the signatures of Science Priorities for Mars Sample Return these phenomena in the form of structure/morphology, biominerals, organic molecular isotopic compositions, and their geologic contexts.

  3. Interpret the conditions of Martian water-rock interactions through the study of their mineral products.

  4. Constrain Science Priorities for Mars Sample Return the absolute ages of major Martian crustal geologic processes, including sedimentation, diagenesis, volcanism/plutonism, regolith formation, hydrothermal alteration, weathering, and cratering.

  5. Understand paleoenvironments and the history of near-surface water on Science Priorities for Mars Sample Return Mars by characterizing the clastic and chemical components, depositional processes, and post-depositional histories of sedimentary sequences.

  6. Constrain the mechanisms of early planetary differentiation and the subsequent evolution of the Martian core, mantle Science Priorities for Mars Sample Return, and crust.

  7. Determine how the Martian regolith is formed and modified and how and why it differs from place to place.

  8. Characterize the risks to future human explorers in Science Priorities for Mars Sample Return 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.

  9. For the present-day Science Priorities for Mars Sample Return Martian surface and accessible shallow subsurface environments, determine the state of oxidation as a function of depth, permeability, and other factors in order to interpret the rates and pathways of chemical weathering Science Priorities for Mars Sample Return, and the potential to preserve the chemical signatures of extant life and pre-biotic chemistry.

  10. Interpret the initial composition of the Martian atmosphere, the rates and processes of atmospheric loss/gain over Science Priorities for Mars Sample Return geologic time, and the rates and processes of atmospheric exchange with surface condensed species.

  11. For Martian climate-modulated polar deposits, determine their age, geochemistry, conditions of formation, and evolution through the detailed examination of Science Priorities for Mars Sample Return the composition of water, CO2, and dust constituents, isotopic ratios, and detailed stratigraphy of the upper layers of the surface.

MSR would have its greatest value if rock samples would be collected Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return, and phyllosilicates. Sediment samples would be 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return. Igneous rocks are expected to be primarily lavas and shallow intrusive rocks of basaltic composition. They would be critical for investigations of the geologic evolution of the Martian surface and interior Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return atmosphere, the nature of rock fragments, dust and sand particles that have been moved over the surface, H2O and CO2 migration between ice and atmosphere, and processes involving fluids and sublimation. Regolith Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 105 to 106 years. Atmospheric gas samples Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return potential Martian biosphere. Samples of Ne, Kr, CO2, CH4 and C2H6 would confer major scientific benefits. Chemical and mineralogical analyses of Martian dust would help to elucidate the weathering and alteration Science Priorities for Mars Sample Return history of Mars. Given the global homogeneity of Martian dust, a single sample would likely be representative of the planet. A depth-resolved suite of samples should be obtained from depths Science Priorities for Mars Sample Return of cm to several m within regolith or from rock outcrop in order to investigate trends in the abundance of oxidants (e.g., OH, HO2, H2O2 and peroxy radicals) and the Science Priorities for Mars Sample Return preservation of organic matter. Other sample suites would include rock breccias that might sample rock types that would otherwise not be available, volcanic tephra consisting of fine-grained regolith material or layers and Science Priorities for Mars Sample Return beds possibly delivered from beyond the landing site, and meteorites whose alteration history could be determined and thereby provide insights into Martian climatic history.

The following factors would be key Science Priorities for Mars Sample Return 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 would require an Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return minimum number of samples needed to address the scientific objectives of MSR would be 26 (20 rock, 3 regolith, 1 dust, 2 gas), in the case of recovery of the MSL cache. These samples would be expected Science Priorities for Mars Sample Return to have a mass of about 350 g, and with sample packaging, the total returned mass would be expected to be about 650 g.

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

5. Degree of selectivity of samples and documentation of field context. The scientific value of MSR would depend critically upon the ability to Science Priorities for Mars Sample Return select wisely the relatively few returned samples from the vast array of materials it would encounter. MSR objectives would require at least three kinds of in situ observations (color Science Priorities for Mars Sample Return imaging, microscopic imaging, and mineralogy measurement), and possibly as many as five (also elemental analysis and reduced carbon analysis). No significant difference would exist in the observations needed for sample selection vs sample documentation Science Priorities for Mars Sample Return. Revisiting a previously occupied site might 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 Science Priorities for Mars Sample Return include organic material, sulfates, chlorides, clays, ice, and liquid water. MSR’s objectives could most confidently be met if the samples would be kept below -20oC, and with less confidence if they would Science Priorities for Mars Sample Return be kept below +20oC. Significant damage, particularly to biological studies, would occur if the samples reach +50oC for 3 hours. Temperature monitoring during return would allow any changes to be evaluated Science Priorities for Mars Sample Return.

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 Science Priorities for Mars Sample Return protocols. It would be 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 Science Priorities for Mars Sample Return operations. In order to collect the suites of rocks that would be required by the MSR objectives, the lander must have significant surface mobility, the capability to assess the diversity of surface Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return, 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 Science Priorities for Mars Sample Return 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 Science Priorities for Mars Sample Return 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), it is unlikely that MSR Science Priorities for Mars Sample Return would 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 Science Priorities for Mars Sample Return-sampling returned samples for these analyses should be re-assessed.

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