5
Planetary Protection and Human Missions to Mars
The committee’s statement of task calls for a brief commentary on whether locations on Mars that are potentially suitable for robotic missions with higher bioburdens than permitted by Category IV might also be suitable for human missions without causing large-scale biological contamination. To begin, the committee recalls reports on planetary protection published in 2018, 2019, and 2020 (see Chapter 1) that identified the lack of a more developed policy for human missions.
The 2002 report Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface (NRC 2002b) focused on the precursor measurements necessary prior to the advent of human operations on the Martian surface. One particularly relevant recommendation from that report is:
The committee recommends that NASA establish zones of minimal biologic risk (ZMBRs) with respect to the possible presence of Martian life during human missions to Mars. In order to do so, NASA should conduct a precursor in situ experiment at a location as reasonably close to the human mission landing sites as possible to determine if organic carbon is present. The measurement should be on materials from the surface and down to a depth to which astronauts may be exposed. If no organic carbon is detected at or above the life-detection threshold, the landing site may be considered a ZMBR. If no measurement technique can be used to determine if organic carbon is present above the life-detection threshold, or if organic carbon is detected above that threshold, a contained sample should be returned to Earth for characterization prior to sending humans to Mars (NRC 2002b).
Since 2002, the science from two NASA landers, four NASA rovers, three NASA orbiters, and several international missions has greatly advanced our understanding of Mars. Curiosity has detected the presence of ancient organic molecules at Gale Crater and has detected methane in the atmosphere.
While scientists have learned a great deal in the two decades since the Safe on Mars report, it remains essential that any proposed human landing site be evaluated and characterized in advance of human presence through both remote sensing and in situ experiments, to establish the zones of minimal biological risk.
NASA adopted an interim directive on planetary protection for human missions to Mars in July 2020. The interim directive does not contain a planetary protection strategy for such missions but instead provides that:
NASA will develop risk-informed decision making implementation strategies for human missions to Mars, which account for and balance the needs of human space exploration, science, commercial activities, and safety. Specifically, NASA will develop guidelines and utilize data and experience gained via ground-based tests, the International Space Station (ISS), Artemis, and other missions.1
Given the underdeveloped nature of planetary protection policy for human missions to Mars, caution is necessary in addressing, even briefly, the suitability of applying guidelines for planetary
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1 NASA, “Biological Planetary Protection for Human Missions to Mars,” NASA Interim Directive (NID) 8715.129, Effective Date July 9, 2020, https://nodis3.gsfc.nasa.gov/OPD_docs/NID_8715_129_.pdf.
protection for robotic missions to human missions. Robotic missions launch with fixed and limited bioburdens that environmental conditions in flight and on the Martian surface contain, reduce, and destroy over time. By contrast, the presence, movement, and activities of microbially diverse humans have the potential to increase biological contamination on and beneath the Martian surface over time. This difference counsels against relying on less restrictive bioburden standards for robotic missions as criteria for setting planetary protection policy for human missions.
In addition, subsurface areas are the most interesting locations for scientific exploration of extant or extinct life on Mars and constitute the most important to protect from harmful forward contamination. As Chapter 3 discussed, lowering bioburden requirements on robotic missions involving these areas and resources proves more challenging for planetary protection policy. Further, sustained access to, and in situ use of, subsurface water ice and possibly caves are considered critical for human missions. Meeting this need may expose such resources and areas to sustained contamination from astronauts and bioburdens of robotic, non-scientific activities (e.g., in situ resource utilization) that support human missions.
This reality underscores the need to accelerate and expand scientific work on subsurface areas and resources and develop a planetary protection strategy to avoid contamination from human missions becoming harmful to scientific exploration for life on Mars. In its interim directive on human missions to Mars, NASA indicated that it would undertake activities to close knowledge or capability gaps identified in developing planetary protection policy for human missions to Mars, including on:
- Capabilities to monitor biological processes associated with the human presence in space exploration and to evaluate changes over time;
- Technologies for mitigating contamination release or intrusion, potentially including closed-loop systems; cleaning/re-cleaning capabilities; quarantine, support systems, and biological waste disposal that minimize impact of humans on the environment of Mars; and
- An understanding of environmental processes on Mars that would contribute to transport and sterilization of terrestrial organisms released by human activity.2
As recent planetary protection reports have suggested (NASEM 2018), potential approaches to designing a planetary protection strategy for human missions include appropriate buffer zones between areas of human activity and locations of astrobiological significance, as well as continued scientific exploration and scientific understanding for life on Mars by humans and robotic technologies. Beyond that, the committee learned in briefings about the potential to use, where appropriate, in situ techniques to reduce contamination from activities undertaken by, and needed to sustain, humans. The need for developing a strategy for human missions through more scientific study, assessment of scientific evidence, multi-stakeholder participation, and international cooperation and harmonization remains pressing.
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2 Ibid.
