Abstract
The NASA/ESA Mars Sample Return (MSR) Campaign seeks to establish whether life on Mars existed where and when environmental conditions allowed. Laboratory measurements on the returned samples are useful if what is measured is evidence of phenomena on Mars rather than of the effects of sterilization conditions. This report establishes that there are categories of measurements that can be fruitful despite sample sterilization and other categories that cannot. Sterilization kills living microorganisms and inactivates complex biological structures by breaking chemical bonds. Sterilization has similar effects on chemical bonds in non-biological compounds, including abiotic or pre-biotic reduced carbon compounds, hydrous minerals, and hydrous amorphous solids. We considered the sterilization effects of applying dry heat under two specific temperature-time regimes and the effects of ?-irradiation. Many measurements of volatile-rich materials are sterilization sensitive?they will be compromised by either dehydration or radiolysis upon sterilization. Dry-heat sterilization and ?-irradiation differ somewhat in their effects but affect the same chemical elements. Sterilization-sensitive measurements include the abundances and oxidation-reduction (redox) states of redox-sensitive elements, and isotope abundances and ratios of most of them. All organic molecules, and most minerals and naturally occurring amorphous materials that formed under habitable conditions, contain at least one redox-sensitive element. Thus, sterilization-sensitive evidence about ancient life on Mars and its relationship to its ancient environment will be severely compromised if the samples collected by Mars 2020 rover Perseverance cannot be analyzed in an unsterilized condition.
To ensure that sterilization-sensitive measurements can be made even on samples deemed unsafe for unsterilized release from containment, contingency instruments in addition to those required for curation, time-sensitive science, and the Sample Safety Assessment Protocol would need to be added to the Sample Receiving Facility (SRF). Targeted investigations using analogs of MSR Campaign-relevant returned-sample types should be undertaken to fill knowledge gaps about sterilization effects on important scientific measurements, especially if the sterilization regimens eventually chosen are different from those considered in this report.
To ensure that sterilization-sensitive measurements can be made even on samples deemed unsafe for unsterilized release from containment, contingency instruments in addition to those required for curation, time-sensitive science, and the Sample Safety Assessment Protocol would need to be added to the Sample Receiving Facility (SRF). Targeted investigations using analogs of MSR Campaign-relevant returned-sample types should be undertaken to fill knowledge gaps about sterilization effects on important scientific measurements, especially if the sterilization regimens eventually chosen are different from those considered in this report.
Original language | English |
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Pages (from-to) | 112-164 |
Number of pages | 53 |
Journal | Astrobiology |
Volume | 22 |
Issue number | S1 |
Early online date | 19 May 2022 |
DOIs | |
Publication status | Published - 2 Jun 2022 |
Bibliographical note
AcknowledgmentsThe MSPG2 Sterilization Effects Focus Group would like to thank the entire MSPG2 committee for their input and discussions during and after our bi-weekly meetings; and external reviewers Brian Clement, Lydia Hallis, Elisabeth Hausrath, Karen Olsson-Francis, and Sandra Siljeström, Strategic Team reviewers Gerhard Kminek, Michael Meyer, Roger Summons, and Frances Westall, and All-Group reviewers Ernst Hauber, Aurore Hutzler, Francis McCubbin, Usui Tomohiro, and Arya Udry for their reviews. We thank editor exemplar Monica Grady and fellow Focus Group Leads Kimberly Tait and Nicholas Tosca for ongoing input on this document. We especially acknowledge the subject matter experts Carl Allen, Dan Barfod, Marc Caffee, Darby Dyar, Paul Niles, Alex Pavlov, Michael Plötze, and Susanne Schwenzer for their important input; and, finally, Dave Beaty and
Brandi Carrier for always being there.
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). 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. Funding Information
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).