A new report by the Committee on Planetary Protection of the National Academies, co-chaired by Amanda Hendrix of the Planetary Science Institute and science policy consultant Joseph Alexander, recommends that rules regarding planetary protection—strict procedures to ensure that Earth microbes don’t contaminate other worlds and vice versa—could be relaxed for certain missions to Mars.
The committee considered the natural sterilizing effects of the Martian environment and came to the conclusion that the constraints on bioburden, or the amount of microbial “hitchhikers” allowed on Mars-bound spacecraft, could be lowered for missions working at or near the surface. Only basic sterilization would be necessary for rovers digging or drilling less than a meter underground, unless they’re near a cave entry, or if remote sensing data show that water ice might be present in the shallow subsurface. The panel also said that planetary protection for Mars missions could be addressed using a risk management approach rather than rigid sterilization requirements, which often drive up a project’s cost.
An important thing to remember about NASA planetary protection guidelines is that they only apply to the agency’s own missions. For commercial missions, the U.S. government has yet to designate a regulatory agency that could guarantee compliance with the Outer Space Treaty, which governs all nations’ activities in space. Right now, commercial space missions can avoid planetary protection if they choose, which the report acknowledges as a major shortcoming.
The Academy panel’s conclusions are consistent with what I, along with my colleague Alberto Fairén of the Center of Astrobiology in Madrid, called for in a 2013 commentary titled “The Overprotection of Mars.” We felt that unneeded and expensive sterilization measures hindered the future exploration of Mars, and that strict requirements should only be applied in cases where we could reasonably expect to encounter Martian life.
But on other matters I disagree with the committee’s conclusions. One is that indigenous life on Mars, if it exists, can’t be distinguished from terrestrial contamination. In a 2017 paper a large scientific team, including Fairén and myself, made the argument that we should in fact be able to make such a distinction. Either Martian life would be biochemically distinct from Earth life, in which case the differences should be apparent, or it’s very similar, in which case it could likely be pinned on the lower branches of the tree of life, having diverged from a common ancestor long ago. The committee does have a point, though. Terrestrial contamination would make it harder to identify and characterize putative Martian life, and so should be avoided.
The other finding I disagree with is that there could not be any life in the ice-free upper meter of the Martian surface. The possibilities of life existing in the shallow underground, particularly in salt rocks, was discussed intensively at the 2019 Mars Extant Life Conference in Carlsbad, New Mexico. There are plenty of salt rocks on Mars, especially in the Southern Highlands, where salt-loving, photosynthesizing microbes could make a living near the surface. Microbes in salt can obtain life-sustaining water directly from the atmosphere, as many salts, including common sodium chloride, are able to draw moisture from the air. So Martian life may not need water from the soil at all.
On questions like this, I feel, we tend to exhibit a certain Earth arrogance in our assumptions about life on Mars. If indigenous Martian life does exist, it would most likely be much better adapted to its home planet than late arrivals from Earth would be. It would have had billions of years to figure out evolutionary adaptations for the Red Planet, unlike Earth organisms accustomed to much warmer and wetter conditions, and generally not used to dealing with a combination of dryness, ultraviolet light, and harsh chemicals. For that reason, the threat of us contaminating Martian life might be less than we fear.