This report from the Committee on Planetary Protection (CoPP) responds 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.”1 NASA specifically asked the committee to include in its report the following:
- An overview of the current scientific understanding, value, and potential threat of organic and biological contamination of permanently shadowed regions (PSRs), lunar research relevant to understanding prebiotic evolution and the origin of life, and the likelihood that spacecraft landing on the lunar surface will transfer volatiles to polar cold traps; and
- An assessment of how much and which regions of the Moon’s surface and subsurface warrant protection from organic and biological contamination because of their scientific value
In fulfilling this task, the committee applied the definition of planetary protection that NASA has used for decades, namely,
- The control of forward contamination, defined as the control of contamination from biological or organic materials that might interfere with the search for life in the solar system; and
- The control of back contamination, defined as the control of extraterrestrial materials collected from other solar system bodies and returned to Earth.2
Current scientific understanding is insufficient for the committee to issue clear findings on some aspects of its charge. However, minimizing and mitigating the potential confounding impact on PSRs is important, so as to avoid obscuring an important scientific record preserved in the volatile deposits. 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 considered different sources of organic and biological contamination of the lunar surface and subsurface from robotic and crewed missions, including rocket exhaust from landers, outgassing from vehicles and structures, and venting from spacesuits. Given the limited time available to the committee to complete its analyses, the committee focused on rocket exhaust from landers as the most significant, and most readily modelled, potential source of organic contamination. Given the scope of planetary protection policy, the committee focused on possible 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.
The existing science indicates that biological contamination of the lunar surface and subsurface is not a threat to scientific investigations of the Moon relevant for planetary protection purposes, such as studies of prebiotic chemical processes. In terms of volatiles, surface contamination of all lunar regions
1 See the statement of task to the committee, reprinted in Appendix A.
2 National Academies of Sciences, Engineering, and Medicine, 2018, Review and Assessment of Planetary Protection Policy Development Processes, The National Academies Press, Washington, DC, https://doi.org/10.17226/25172.
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. However, little is actually known about the composition, distribution, and transport of volatiles on the Moon, especially concerning surface and subsurface areas of PSRs. Scientific investigations are urgently needed to provide “ground truth” measurements about volatiles on and underneath PSRs in order to inform the development of appropriate and effective planetary protection strategies.
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.
In arriving at the findings above, the committee concludes that a critical issue is the absence of formally defined and accepted, prioritized, science objectives. While development of such a strategy is not the proper role of this committee, it does lead to the committee’s final, overarching finding.
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.