Planetary Protection for the Study of Lunar Volatiles: A National Academies Space Studies Board Report

This paper summarizes findings by the Committee on Planetary Protection of the National Academies of Sciences, Engineering, and Medicine in response to NASA's request for "a short report on the impact of human activities on lunar polar volatiles [e.g., water, carbon dioxide, and methane] and the scientific value of protecting the surface and subsurface regions of the Earth's Moon from organic and biological contamination." The committee focused on rocket exhaust from landers as the most significant, and most readily modelled, potential source of organic contamination. The committee considered direct and indirect contamination of the surface and subsurface of PSRs because these regions: (1) are of most interest for scientific investigations of how lunar volatiles inform the processes of prebiotic chemistry; and (2) act as "cold traps" that can capture and preserve scientifically important volatiles from natural and anthropogenic sources. Surface contamination of all lunar regions from human activities, such as rocket exhaust, is likely, but the risk of contaminating subsurface deposits in PSRs from vertical transport through natural processes is low. Potential contamination mitigation steps that merit further attention include using spacecraft emissions modeling in combination with laboratory, remote sensing, and in-situ data, to tailor individual mission planetary protection approaches; characterizing the signature of exhaust volatiles; use of spacecraft witness plates; and implementing contamination mitigation protocols during sampling. The committee's specific findings are as follows: Finding 1: The scientific potential of the Moon's poles and PSRs is significant, including for studies of prebiotic chemical evolution that have long been within the scope of national and international planetary protection policy. Finding 2: Understanding of the lunar poles and PSRs has advanced but remains incomplete concerning many scientific questions, including how cold traps on the lunar surface function with respect to volatile and organic chemicals, the nature and composition of water and other volatile deposits in PSRs, and how the water and other ice deposits inform the scientific understanding of prebiotic chemical evolution in the solar system. Finding 3: Tapping the scientific potential of the lunar poles and PSRs requires accelerating lunar science across orbital and in-situ missions and building "ground truth" about these regions to inform planning for planetary protection approaches for future scientific, exploration, and commercial activities on the Moon. Finding 4: Inventories of biological materials for spacecraft and other lunar equipment are unimportant for planetary protection purposes because (1) the Moon's surface does not support indigenous forms of life or the proliferation of terrestrial organisms brought to the Moon; (2) biological contamination of the lunar surface will not contaminate the lunar subsurface through the operation of natural processes on the Moon; and (3) any biological material identified in samples from the lunar surface or subsurface can be tested against terrestrial organisms to determine its source. Finding 5: There is a lack of, and need for, studies to characterize the chemical composition, transport, and the level of contamination of volatiles that would be harmful to future investigations of prebiotic chemical evolution to be pursued at PSRs. This information is necessary to determine whether to establish planetary protection requirements for missions to these areas of the Moon, such as a requirement for reporting the inventory of propellants, combustion products, and potential off-gassing volatiles from spacecraft. Finding 6: A clear articulation of prioritized science objectives to frame a strategy for exploration of the lunar PSRs does not exist and is required for an effective planetary protection policy for the Moon.