Science Priorities for Mars Sample Return
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APPENDIX 1 (ND-SAG CHARTER) Science Issues and Priorities for a Next Decade MSR Science Analysis Group (ND-SAG) Introduction On July 10, 2007, Dr. Alan Stern, AA-SMD, described to the participants in the 7th 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
Requested Tasks
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.
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. TO VIEW, CLICK ON THE FOLLOWING LINK. Sci_Prior_MSR–App_II 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III The first Mars Surface-Sample Return mission: revised science considerations in light of the 2004 MER results Unpublished report, 62 pages in length.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: Mars Sample Return Science Steering Group II (Glenn MacPherson, Chair) Report Date: February 16, 2005 THIS APPENDIX IS PRESENTED AS A SEPARATE DOCUMENT. TO VIEW, CLICK ON THE FOLLOWING LINK. Sci_Prior_MSR–App_III 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:
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.  APPENDIX V Comparison of the analysis of the Martian atmosphere by MSL and in a returned sample on Earth. Krypton and Xenon. 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 129Xe from decay of extinct 129I, 80Kr and 82Kr from neutron capture on Br, heavy Xe (e.g., 136Xe) from fission of extinct 244Pu, and possibly light Xe (e.g., 124Xe) 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 124Xe-136Xe mass range, or ~4% per a.m.u.. In the analysis here, we assume each 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 124Xe/136Xe or 126Xe/136Xe could answer the question of the Xe starting composition. Also, a 1% precision in 129Xe/132Xe would give the 129I 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 79Br and 81Br. If we must determine the starting composition from the 83Kr/86Kr 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. There are two main science questions: to what extent has atmospheric loss fractionated 36Ar/38Ar, and how much 40Ar has been added from decay of 40K. These are interacting data sets. We believe the current 36Ar/38Ar 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 40Ar/36Ar (e.g., 1800 ±18) would be quite adequate in determining the amount of radiogenic 40Ar. Thus, there would be modest rationale for a returned Ar sample. Nitrogen. The main science question is the degree of 15N/14N 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. 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 20Ne will have a problem with interference from doubly ionized 40Ar. SAM will try to generate some information on 21Ne/20Ne 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. 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. C and O in CO2 and H2O. Viking reported 13C/12C and 18O/16O in CO2 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 CO2 probably would require their measurement to better than 0.1%. We conclude that sample return of CO2 would be highly desirable to answer both science questions posed. As for H2O, 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 H2O would be better done on Mars. D/H. 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. 2008 MEPAG ND-SAG report Page |