Mars 2020 Mission Biological Return Sample Contamination Control Approach and Verification

The Mars 2020 Perseverance rover is equipped with a Sample Caching System (SCS) designed to collect and cache Martian core and regolith samples for potential return to Earth. To ensure the integrity of these samples, the mission requirements for each encapsulated sample for return is less than one Earth-sourced viable organism (VO) and more than a 99.9% probability of being free of any Earth-sourced VO. To satisfy the stringent biological contamination requirements in support of return sample science (RSS) investigations, special bioburden mitigation and reduction approaches were developed and implemented for SCS hardware that would directly contact or be in close proximity to the Martian samples. Here, we describe the implemented approaches for microbiological contamination reduction and mitigation, detail the processes of the SCS aseptic assembly, and report the estimated VO for each returned sample. We found that our conservative estimate (CE) of the computed probability of a single VO in the returned sample is more than one order of magnitude lower than the biological contamination requirement while the best estimate (BE) exceeds two orders of magnitude.