Samples returned from Mars would be placed under quarantine at a Sample Receiving Facility (SRF) until they are considered safe to release to other laboratories for further study. The process of determining whether samples are safe for release, which may involve detailed analysis and/or sterilization, is expected to take several months. However, the process of breaking the sample tube seal and extracting the headspace gas will perturb local equilibrium conditions between gas and rock and set in motion irreversible processes that proceed as a function of time. Unless these time-sensitive processes are understood, planned for, and/or monitored during the quarantine period, scientific information expected from further analysis may be lost forever. At least four processes underpin the time-sensitivity of Mars returned sample science: (1) degradation of organic material of potential biological origin, (2) modification of sample headspace gas composition, (3) mineral-volatile exchange, and (4) oxidation/reduction of redox-sensitive materials. Available constraints on the timescales associated with these processes supports the conclusion that an SRF must have the capability to characterize attributes such as sample tube headspace gas composition, organic material of potential biological origin, as well as volatiles and their solid-phase hosts. Because most time-sensitive investigations are also sensitive to sterilization, these must be completed inside the SRF and on timescales of several months or less. To that end, we detail recommendations for how sample preparation and analysis could complete these investigations as efficiently as possible within an SRF. Finally, because constraints on characteristic timescales that define time-sensitivity for some processes are uncertain, future work should focus on: (1) quantifying the timescales of volatile exchange for core material physically and mineralogically similar to samples expected to be returned from Mars, and (2) identifying and developing stabilization or temporary storage strategies that mitigate volatile exchange until analysis can be completed.
We would like to thank the entire MSPG-2 committee for their input and discussions during our bi-weekly meetings, especially Kim Tait and Michael Velbel and for their input on this document. We are grateful for the generous input from subject matter experts Paul Niles (NASA-JSC) and Matthew Brady (University of Cambridge) on evolved gas analysis of volatile-bearing minerals, and to Lisa Mayhew, Karim Benzerara, and Ralph Milliken for comments and feedback which improved the clarity of the report. The decision to implement Mars Sample Return will not be finalized until NASA’s completion of the National Environmental Policy Act (NEPA) process. This document is being made available for planning and information purposes only.
A portion of this work was funded by the National Aeronautics and Space
Administration (NASA) and the European Space Agency (ESA). A portion 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 (80NM0018D0004). This work has partly (H. B.) been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation. M.A.V.’s participation in MSPG2 was supported in part by a sabbatical leave-of-absence from Michigan State University. M.-P.Z. was supported by projects PID2019-104205GB-C21 of Ministry of Science and Innovation and MDM-2017-0737 Unidad de Excelencia ‘Maria de Maeztu’–Centro de Astrobiología (CSIC-INTA) (Spain).