Abstract
The Perseverance rover is meant to collect samples of the martian surface for eventual return to Earth. The headspace gas present over the solid samples within the sample tubes will be of significant scientific interest for what it reveals about the interactions of the solid samples with the trapped atmosphere and for what it will reveal about the martian atmosphere itself. However, establishing the composition of the martian atmosphere will require other dedicated samples. The headspace gas as the sole atmospheric sample is problematic for many reasons. The quantity of gas present within the sample tube volume is insufficient for many investigations, and there will be exchange between solid samples, headspace gas, and tube walls. Importantly, the sample tube materials and preparation were not designed for optimal Mars atmospheric gas collection and storage as they were not sent to Mars in a degassed evacuated state and have been exposed to both Earth's and Mars' atmospheres. Additionally, there is a risk of unconstrained seal leakage in transit back to Earth, which would allow fractionation of the sample (leak-out) and contamination (leak-in). The science return can be improved significantly (and, in some cases, dramatically) by adding one or more of several strategies listed here in increasing order of effectiveness and difficulty of implementation: (1) Having Perseverance collect a gas sample in an empty sample tube, (2) Collecting gas in a newly-designed, valved, sample-tube-sized vessel that is flown on either the Sample Fetch Rover (SFR) or the Sample Retrieval Lander (SRL), (3) Adding a larger (50-100 cc) dedicated gas sampling volume to the Orbiting Sample container (OS), (4) Adding a larger (50-100 cc) dedicated gas sampling volume to the OS that can be filled with compressed martian atmosphere.
Highlights
The Mars Sample Return (MSR) Program has as a current draft Level 1 Requirement: “The MSR Campaign shall be capable of delivering to Earth at least one dedicated atmospheric gas sample of at least 1.9 × 10-5 mole of martian atmospheric gas molecules that is collected and stored in a clean and sealed volume.”
This team has been tasked with studying the scientific implications of returning, instead, one or more sample tubes from Perseverance, which would be sealed on Mars in the presence of martian atmosphere
We address two specific issues: (1) An individual sample tube on Perseverance would collect approximately 20% of the amount in the current draft Level 1 requirement, so we address the minimum amount of atmospheric sample needed to constrain high-priority scientific questions
Summary
The Mars Sample Return (MSR) Program has as a current draft Level 1 Requirement: “The MSR Campaign shall be capable of delivering to Earth at least one dedicated atmospheric gas sample of at least 1.9 × 10-5 mole of martian atmospheric gas molecules that is collected and stored in a clean and sealed volume.” This team has been tasked with studying the scientific implications of returning, instead, one or more sample tubes from Perseverance, which would be sealed on Mars in the presence of martian atmosphere. O If NASA and ESA decide to remove the draft Level 1 Requirement, we would strongly recommend that M2020 collects at least one gas sample using an empty sample tube Such a collected sample would meet some of the draft Level 1 Requirement objectives but would provide a critically important control (and standard) for gas geochemistry investigations involving sealed tubes that contain Mars samples and head space gas. Such a vessel would not require additional space to return it compared to a typical sealed empty sample tube, it would require development efforts. 6 return), and while it would not meet the draft Level 1 requirement for volume, the inevitable advances in detection technology that will occur before the return of the samples would mitigate this
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