Mars Sample Return backwardcontamination – Strategic adviceand requirements - Report from the ESF-ESSC Study Group on MSR PlanetaryProtection Requirements.

As planetary protection regulations have a signifi- 3 cant impact on mission design, engineering and overall cost, it is critical that the guidelines are implemented with proper justification and are reevaluated on a regular basis. In June 2011, the European Space Agency asked the European Science Foundation (ESF) in coordination with its European Space Sciences Committee (ESSC) to perform a study regarding planetary protection regulations for a Mars Sample Return (MSR) mission. Specifically, ESF was asked to perform a study on the level of assurance of preventing an unintended release of Martial particles into the Earth’s biosphere in the frame of an MSR mission. ESF commissioned a study group of 12 high-level, international and multidisciplinary experts (see Annex 1 for Study Group composition) to evaluate the current requirements, and to provide new insights and recommendations where applicable. The Study Group was formed following a call for nominations addressed to several research organisations in Europe and beyond as well as to the ESF standing committees on Life, Earth and Environmental Sciences (LESC), Medical Research (EMRC), Physical and Engineering Sciences (PESC) as well as Social Sciences (SCSS) and Humanities (SCH). The mandate of the Study Group was to: “Recommend the level of assurance for the exclusion of an unintended release of a potential Mars life form into the Earth’s biosphere for a Mars Sample Return mission”. The starting point of this activity was the requirement used since the late 1990s specifying that: ‘the probability that a single unsterilised particle of 0.2 micron diameter or greater is released into the Earth environment shall be less than 106’. The value for the maximum particle size was derived from the NRC-SSB 1999 report ‘Size Limits of Very Small Microorganisms: Proceedings of a Workshop’, which declared that 0.25 ± 0,05 μm was the lower size limit for life as we know it (NRC, 1999). However, the past decade has shown enormous advances in microbiology, and microbes in the 0.10–0,15 μm range have been discovered in various environments. Therefore, the value for the maximum particle size that could be released into the Earth’s biosphere is revisited and re-evaluated in this report. Also, the current level of assurance of preventing the release of a Mars particle is reconsidered. To complete its mandate, the Study Group met on three occasions between June and November 2011 and commissioned the organisation of a workshop dedicated to risk perception held in January 2012. The outcome and recommendations from the risk perception workshop (see Annex 2 for details) were used as direct inputs in the formulation of the advice contained in this report.