Time-Sensitive Aspects of Mars Sample Return (MSR) Science

Abstract

List of Findings 1. Introduction 1.1 Scope of the report 2. Time-Sensitivity of MSR Investigations: Background 3. Time-Sensitivity of MSR Investigations: Rationale 4. Time-Sensitive Processes and Their Characteristic Timescales 4.1 Degradation of organic material (including volatile compounds) 4.2 Modification of sample headspace gas composition 4.3 Mineral-volatile exchange 4.3.1 Hydrous sulfate minerals 4.3.2 Poorly crystalline and X-ray amorphous materials 4.3.3 Phyllosilicate minerals 4.3.4 Hydrous carbonate minerals 4.4 Oxidation/reduction of redox-sensitive minerals 5. Estimating the Loss of Scientific Information as a Function of Time: Implications for Sample Handling and Curation Workflow within an SRF 6. Recommendations for SRF Sample Processing and Analytical Capabilities 6.1 Goal 1: Characterize sample tube headspace gas composition

Planning Implications Related to Sterilization-Sensitive Science Investigations Associated with Mars Sample Return (MSR)

“…Furthermore, as noted above, all indications to date of carbonate minerals on Mars from orbital spectroscopy correspond to Mg-carbonate; the orbital spectra are consistent with the presence of the hydrous Mg-carbonate hydromagnesite (Calvin et al, 1994;Ehlmann et al, 2008b;Horgan et al, 2020). Hydrous carbonates contain H and O as molecular water, and some also contain hydroxyl (Jull et al, 1988;Velbel et al, 1991;El-Shenawy et al, 2020;Tosca et al, 2021). Water from these minerals is evolved (these minerals are "dehydrated") at temperatures (T D ) less than proposed sterilization temperatures (T S ).…”

“…No matter whether this is absorbed or structural water (H 2 O(-) or H 2 O(+)) or the hydroxyl group (OH), the original mineral has been changed. Tosca et al (2021) provide additional examples of devolatilization of H and O from these minerals. All hydrated (or hydrous) and hydroxylated minerals are sensitive to sterilization by dry heat if they lose water at temperatures below the proposed T S (Figure 10a).…”

“…Implications for the SRF are then discussed (Section 7). One answer to the question posed above is explored in Section 7-to add contingency instruments to contained laboratories to the SRF specifically for sterilization-sensitive science that is not enabled by instruments present in the SRF to support Curation, SSAP, and time-sensitive science (Carrier et al, 2021;Tait et al, 2021;Tosca et al, 2021).…”

“…Therefore, to minimize chemical alteration of the returned samples and maximize their scientific integrity, the temperature and duration of heating of the samples post-collection on Mars should be kept as low as possible. Refrigeration of subsamples in the SRF is recommended for samples with attributes (including extant or recently deceased microorganisms) that would deteriorate on short (minutes to months) timescales if maintained at laboratory ambient temperature (Tosca et al, 2021).…”

“…The EGA heating sequence could then either be terminated, with the sterilized solid sample released to a laboratory outside containment for analysis (including normal TC/EGA at temperatures higher than the sterilization temperature), or (if the subsample is specifically for EGA) continued to complete the TC/EGA sequence for the subsample in a single analytical session on the same instrument. An IRMS dedicated and optimized for simple low molecular weight volatiles and their light stable isotopes is expected to be in the SRF to support time-sensitive science in containment, for identification, concentration and light stable isotope ratios of major and minor gaseous species in complex evolved-gas mixtures of volatile compounds; and compound-specific C-, N-, S-, O-, and H-isotope ratios (Tosca et al, 2021). Using the TC step of TC/EGA as the implementation of dry heat sterilization can be considered sterilization by science, science by sterilization, an(other) alternative to, or novel implementation of, dry heat sterilization, and another specific pathway to dry heat sterilization.…”