Sterilizing Mars Sample Return (MSR): Implication on Finding Life

This image shows a photo montage of each sample tube deposited by NASA’s Perseverance rover as viewed by the Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) camera. Credit: NASA/JPL-Caltech/MSSS.

One of the primary objectives of the Mars Sample Return (MSR) campaign is to determine whether life on Mars exists or existed in the past. Addressing this key question would require assessing the presence of any life forms, organic and pre-biotic carbon, or preserved biosignatures in samples from sites with habitable environments and evidence of significant aqueous activity at some point in martian history. However, to protect our planet’s biological integrity, NASA’s Planetary Protection policies prevent the release of returned martian samples to non-Biosafety Level-4 terrestrial laboratories, which includes most labs outside of highly secure national labs, without a sterilization process. The NASA and ESA Planetary Protection Officers (PPOs) determined that the sterilization should include dry heat in two temperature-time regimes (180ยฐC for 3 hours; 250ยฐC for 30 minutes) and ฮณ-irradiation (1 MGy).

Members of the MSR Campaign Science Group, Michael Velbel and team, conducted a study that determined that sterilization-sensitive evidence about ancient life on Mars and its relationship to its ancient environment would be severely compromised if the samples collected by the Mars 2020 Perseverance rover cannot be analyzed in an unsterilized condition. They predict that dry heat and ฮณ-irradiation will result in the loss of volatiles and evidence of any living microorganisms and organic complex structures by breaking bonds, changing oxidation states, and altering isotope abundances. The team concluded that contingency instruments, in addition to those required for curation, time-sensitive science, and sample safety assessment protocol, should be included within the Sample Receiving Facility (SRF) to take sterilization-sensitive measurements before the sterilization required to distribute subsamples for scientific investigations outside the SRF. READ MORE