Biological safety in the context of backward planetary protection and Mars Sample Return: conclusions from the Sterilization Working Group

Abstract

The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) are studying how samples might be brought back to Earth from Mars safely. Backward planetary protection is key in this complex endeavour, as it is required to prevent potential adverse effects from returning materials to Earth's biosphere. As the question of whether or not life exists on Mars today or whether it ever did in the past is still unanswered, the effort to return samples from Mars is expected to be categorized as a ‘Restricted Earth Return’ mission, for which NASA policy requires the containment of any unsterilized material returned to Earth. NASA is investigating several solutions to contain Mars samples and sterilize any uncontained Martian particles. This effort has significant implications for both NASA's scientific mission, and the Earth's environment; and so special care and vigilance are needed in planning and execution in order to assure acceptance of safety to Earth's biosphere. To generate a technically acceptable sterilization process across a wide array of scientific and other stakeholders, on 30–31 January 2019, 10–11 June 2019 and 19–20 February 2020, NASA informally convened a Sterilization Working Group (SWG) composed of experts from industry, academia and government to assess methods for sterilization and inactivation, to identify future work needed to verify these methods against biological challenges, and to determine their feasibility for implementation on robotic spacecraft in deep space. The goals of the SWG were: (1)Understand what it means to sterilize and/or inactivate Martian materials and how that understanding can be applied to the Mars Sample Return (MSR) mission.(2)Assess methods for sterilization and inactivation, and identify future work needed to verify these methods.(3)Provide an effective plan for communicating with other agencies and the public.This paper provides a summary of the discussions and conclusions of the SWG over these three workshops. It reflects a consensus position based on qualitative discussion of how agencies might approach the problem of sterilization of Mars material. The SWG reached a consensus that sterilization options can be considered on the basis of biology as we know it, and that sterilization modalities that are effective on terrestrial materials and organisms should be part of the MSR planetary protection strategy. Conclusions pointed to several industry standards for sterilization to include heat, chemical, UV radiation and low-heat plasma. Technical trade-offs for each sterilization modality were discussed while simultaneously considering the engineering challenges and limitations for spaceflight. Future work includes more in-depth discussions on technical trade-offs of sterilization modalities, identifying and testing Earth analogue challenge organisms and proteinaceous molecules against chosen modalities, and executing collaborative agreements between NASA and external working group partners to help close data gaps, and to establish strong, scientifically grounded sterilization and inactivation standards for MSR.

Mars: new insights and unresolved questions

“…Planetary protection was established and needs to continue in effective implementation, to prevent space exploration causing this sort of pandemic scenario. A thorough assessment of various modes of inactivation and containment of martian sampling is ongoing (Craven et al, 2021).…”

Chirality in Organic and Mineral Systems: A Review of Reactivity and Alteration Processes Relevant to Prebiotic Chemistry and Life Detection Missions

“…When determining chirality in organic compounds during life detection missions, contamination could arise from malfunctioning instrumentation [515], sampling [365], or terrestrial contamination [516]. Strategies employed for dealing with contamination include the use of sterilization procedures, e.g., decontamination heaters, UV radiation, chemical, and low-heat plasma ( [517] and references therein) and limiting the use of solvents and/or derivatization agents [500].…”

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

“…More recently, conclusions from NASA's Sterilization Working Group (Craven et al, 2021), with input from sterilization experts across industry, government, and academia, indicated that terrestrial sterilization technologies should be extremely effective at inactivating all martian biology, because they likely share fundamental chemistries of chemical bonds. These proven modalities act by directly impacting chemical bonds in essential structures for life including nucleic acid, proteins, and lipid structures.…”