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.
Since 1982, NASA has required varying levels of stringency for reducing a spacecraft’s bioburden, such as “clean room” assembly or partial sterilization of components. The new report is geared specifically toward preventing harmful terrestrial contamination that has the potential to proliferate on Mars and interfere with searches for indigenous life on the planet.

“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.”

“Planetary protection measures should be aimed at reducing risks while preserving, to the greatest extent reasonable, the prospect that important scientific goals can be realized,” added committee co-chair Joseph Alexander of Alexander Space Policy Consultants.

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 on the surface of Mars, 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.

The study — undertaken by the Committee on Planetary Protection — was sponsored by NASA.

The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.