‘Evaluation of Bioburden Requirements for Mars Missions’ report identifies new approach for NASA to prevent contaminating Mars with Earth-based microbes
A new report from the National Academies of Sciences, Engineering, and Medicine identifies criteria that could allow robotic missions to certain locations on Mars to be carried out with less restrictive “bioburden” requirements, which are designed to prevent the unintentional transport of Earth-based microbes to Mars.
Mars—with its significant amount of water ice, evidence of past liquid water, and close proximity to Earth—is a critically important destination in the search for past or present extraterrestrial life. In order to preserve the integrity of experiments searching for life, missions to the surface of Mars are required to meet strict planetary protection requirements to reduce the amount of biological contamination brought from Earth (also called the “bioburden”).
Since the 1980s, national and international planetary protection policies have sought to avoid contamination by terrestrial organisms that could compromise future investigations regarding the origin or presence of Martian life. Over the last decade, the number of national space agencies planning, participating in, and undertaking missions to Mars has increased, and private-sector enterprises are engaged in activities designed to enable commercial missions to Mars. The nature of missions to Mars is also evolving to feature more diversity in purposes and technologies. As missions to Mars increase and diversify, national and international processes for developing planetary protection measures recognize the need to consider the interests of scientific discovery, commercial activity, and human exploration. The implications of these changes for planetary protection should be considered in the context of how much science has learned about Mars, and about terrestrial life, in recent years.
“Changes to planetary protection policies should be considered in the context of how much science has learned in recent years about Mars,” said Amanda Hendrix, a senior scientist at the Planetary Science Institute and co-chair of the committee that wrote the report. “Because of this increased knowledge, NASA now has an opportunity to take a more nuanced and, in some cases, more permissive approach to reducing bioburden requirements for certain missions. However, caution is still warranted because we have a lot to learn about Mars, and about terrestrial life’s survivability.”
Harsh conditions on much of the surface of Mars, including high levels of ultraviolet (UV) radiation, the paucity of persistent liquid water, and extreme humidity and temperature cycles, make the survival, growth, and proliferation of terrestrial organisms unlikely, the report says. In addition, portions of the Martian subsurface, down to a depth of approximately 1 meter, where no ice is present, are also not environments where terrestrial organisms could proliferate.
However, Earth-based microbes could conceivably thrive in subsurface locations on Mars such as cave systems. For robotic missions that do not enter such locations or “buffer zones” around subsurface access points, and that do not go below 1 meter of the planet’s subsurface, relaxed bioburden requirements could be appropriate, the report says. Buffer zones would need to be determined based on wind conditions and estimates of microbial survival time in the landing environment.
Continued pre-launch cleanliness provisions would help mitigate risk, as could decontamination of equipment such as drill bits after landing, and the careful design of missions so as to take advantage of the effects of naturally sterilizing UV and cosmic radiation. The effectiveness of such in situ methods to reduce terrestrial contamination should be validated before they are relied upon, the report says, and better estimates of habitat connectivity and of subsurface brine and ice, as well as improved knowledge of subsurface access points, are needed to evaluate risks of harmful contamination.
For any missions that are performed with reduced bioburden requirements, NASA should consider adopting established risk management practices, which could provide more benefits in an increasingly complex planetary protection context.
The committee’s findings apply specifically to missions for which NASA has responsibility for planetary protection. For commercial missions in which NASA has no role or connection, the U.S. government still needs to designate a regulatory agency to authorize and continually supervise space activities in accordance with the Outer Space Treaty, the report says.
Evaluation of Bioburden Requirements for Mars Missions, National Academies of Sciences, Engineering, and Medicine; Division on Engineering and Physical Sciences; Division on Earth and Life Studies; Space Studies Board; Board on Life Sciences; Committee on Planetary Protection, October 2021
Incorporation of Planetary Protection Knowledge Gaps into Agency Capability Development Planning Dec 2020 COSPAR and ESA/NASA Virtual Meeting on Planetary Protection for Human Missions to Mars