Formulating Mitigation Approaches for Protection from Organic and Biological Contamination of Permanently Shadowed Regions
Chapter 2 of this report discusses the scientific value and importance of studies of the lunar polar regions, including permanently shadowed regions (PSRs). Studies in the PSRs, in particular, have the potential to advance understanding of the impact history of the inner solar system and prebiotic chemistry in the solar system and on Earth, which set the stage for the emergence of life. However, no ground-truth chemical analyses of the lunar materials and volatiles at the PSRs currently exist, either on the surface or at depth. As a 2018 LEAG report indicated, “landed missions [are needed to] provide information about the physical properties of the regolith; vertical and lateral distribution of volatiles; in-situ measurements of chemical, isotopic, and mineralogic characteristics of polar deposits [to provide] details on the origin and complexity of lunar volatiles.”1
The substantial increase in planned near-term missions to the lunar surface, along with an expanding stakeholder community, places new urgency on assessing what is known and what is still needed from scientific exploration of the lunar poles and the PSRs. This challenge raises questions: Has the scientific exploration of the Moon already advanced enough that the contemplated high level of activity on the Moon (including human presence) will not jeopardize the ability to answer critical, outstanding scientific questions? Should certain areas on the Moon be preserved against confounding contamination to protect future astrobiologically oriented scientific studies?
Although there is potential for deleterious impact on volatiles-science from human and robotic activities in the lunar polar regions, science objectives relating to volatiles are just one important component of a broad continuum of fundamental scientific advances that are envisioned for a sustained human lunar presence, which also include objectives of advancing astrophysics, heliophysics, fundamental physics, geophysics, geology, and economic geology.
Even leaving aside plans for in situ resource utilization on the Moon, the intensive exploration of the Moon, as contemplated in NASA’s plans, will entail many propulsive landings and maneuverings on and near the lunar surface and involve deploying substantial aggregate amounts of volatile materials likely to condense out in the PSR cold traps. Accordingly, minimizing and mitigating the potential confounding impact on those regions is important, so as to avoid obscuring an important scientific record preserved in the volatile deposits. Chapter 3 provides order-of-magnitude models of the likely composition and concentrations of potential lander plume contaminants.
Current exploration plans involve rapidly advancing from small robotic landers to large robotic landers and to human landers. The planned advent of human landers and human habitats, accompanied by substantial life support systems that will vent, can widely distribute a large variety of condensable volatiles into the environment. The studies by Prem et al. 20202 described in Chapter 3 show that exhaust material from landers may be distributed over a wide surface area. Chapter 3 also discusses how, as landed systems become bigger, more propellant will be required for landing, which will produce vastly
1 Lunar Exploration Analysis Group, 2017, Advancing Science of the Moon: Report of the Specific Action Team, August 7-8, 2017, Houston, Tex.
2 P. Prem, D.M. Hurley, D.B. Goldstein, and P.L. Varghese, 2020, The evolution of a spacecraft-generated lunar exosphere, Journal of Geophysical Research (Planets) 125: e06464, doi:10.1029/2020JE006464.
larger quantities of condensable exhaust-gas volatiles. Although the vast majority of combustion products are not organic molecules, volatiles need not be organic to be relevant to prebiotic investigations.
There are three general categories for creating contamination, as follows:
- Organismal biological contamination, which is considered the least concerning for lunar science (see Chapter 2). Any biological organisms or substances definitively attributable to organisms detected on the Moon are highly likely to be extra-lunar and brought from Earth by robotic or human missions.
- Contamination by volatiles that result from the breakdown of solid organics on spacecraft or lunar structures, which will happen slowly and be distributed only locally in the region of the landed source.
- Organic volatile and condensable gasses, released during propulsive landings or maneuvers or vented from human landers and habitats, are the most likely potential contaminants for confounding scientific investigation of lunar volatiles that have been and will be deposited naturally at the PSRs. However, modelling by the committee suggests that concentrations of deposited material may be very low (see Chapter 3). Furthermore, to the extent that scientific investigations involve retrieving buried samples from depth, that confounding potential is likely to be minimal, because most contaminants are not expected to penetrate more than a few centimeters below the surface (see Chapters 2).
The third point above reinforces a major implication of Finding 2 (Chapter 2) that studies to identify those high-priority investigations that are susceptible to confoundment by contamination at the top surface layer of lunar geology, especially organic volatiles released during propulsive landings or vented from human landers and habitats, would help to formulate a robust policy and potential mitigation approaches. However, until those studies are performed, securing a credible answer to the final item in the committee’s charge—that is, an assessment of regions of the Moon’s surface and subsurface that warrant protection from organic and biological contamination because of their scientific value—is not feasible.
Finding 6: A clear articulation of prioritized science objectives to frame a strategy for exploration of the lunar PSRs lunar PSRs does not exist and is required for an effective planetary protection policy for the Moon.
Finally, in the chapters above, the committee has outlined other contamination mitigation steps that merit attention. These include the following:
- Using spacecraft emissions modeling in combination with laboratory, remote sensing, and in situ data to tailor individual mission planetary protection approaches (see Chapter 3);
- Characterizing the signature of exhaust volatiles (see Chapter 3);
- Use of spacecraft witness plates as recommended in the LEAG report to COSPAR3; and
- Implementing contamination mitigation protocols during sampling (e.g., building on experience with sampling in subsurface lakes in Antarctica as noted in Chapter 2).
One guiding principle of planetary protection policy has been to take a conservative approach to protection against forward contamination and relax the standards only when sufficient new scientific understanding and consensus supports the change. Planetary protection for the Moon was conservative during the early Apollo missions, relaxed during the later missions, and minimal (Category I) until new scientific discoveries indicated the likelihood of stored volatile deposits at the lunar poles. The new
3 Lunar Exploration Analysis Group, 2017.
scientific information led COSPAR to revise its planetary protection policy in 2008 to recommend that lunar orbital and lander missions be shifted from Category I to Category II—an approach NASA supported. Although there have been no subsequent missions to the lunar polar regions or the PSRs to provide ground truth about these areas, NASA’s new Lunar NID4 does not require Category II spacecraft organic inventories for any landed lunar mission.
A conservative approach to planetary protection for near-term missions is to continue adhering to COSPAR’s current guidance until pertinent, initial, in situ science missions can be conducted to better understand the nature of both the surficial and buried volatiles at the poles. The COSPAR guidelines do not distinguish between combustion byproducts that recent studies indicate can be globally dispersed within hours of landing and solid organic materials that are expected to release volatiles only locally and over much longer timescales. However, in briefings to the committee, COSPAR representatives suggested that in the future “there might be a rationale to reduce the organic inventory documentation to volatile products of the propulsion and life support system.”5 Categorization has always been subject to tailoring, given the nature of each mission’s requirements and objectives.
It is important to keep in mind that Category II only requires documentation. Appendix C presents NASA’s template for the documentation of an organics inventory for a Category II mission, and the organics inventory prepared for the GRAIL mission. This kind of documentation has been standard for NASA missions.
The committee heard competing views as to whether such a requirement is financially or technically prohibitive for non-NASA missions to meet, especially for small missions operating with constrained budgets. The 2020 NASEM report indicated that the committee “could not verify whether planetary protection requirements impose a minimum [potentially prohibitive] cost” on small entrepreneurial missions. The 2020 report Assessment of the Report of NASA’s Planetary Protection Independent Review Board suggested that NASA “undertake a study to see if such a [irreducible base] cost exists.”6
However, NASA’s planetary protection officer indicated to the committee that inventories of organic materials produced for planetary protection purposes are not organized or curated in ways that facilitate accessible, effective use of such inventories for planning space missions. The committee was not able to examine how inventories are managed or curated in the timeframe allotted for this report.
4 NASA, 2020, “NASA Interim Directive on Planetary Protection Categorization for Robotic and Crewed Missions to the Earth’s Moon,” NID 8715.128, July 9.
5 Briefing to the committee by COSPAR Planetary Protection Panel vice chair, Gerhard Kminek, September 23, 2020.
6 National Academies of Sciences, Engineering, and Medicine, 2020, Assessment of the Report of NASA’s Planetary Protection Independent Review Board, The National Academies Press, Washington, DC, pp. 27-28.
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