Keeping Mars clean.

C. P. Mckay (“Biologically Reversible Exploration,” Policy Forum, 6 February, p. [718][1]) recommends that “COSPAR [the international Committee on Space Research] … set a policy that all Mars exploration be biologically reversible.” I agree; it allows rigorous scientific study of past and current life there without presupposing that it will be easily recognizable or accessible. However, several assertions may not go far enough to enable remediation, which could make cleanup politically or fiscally impossible. Key are clear statements as to the purpose and urgency of exploration that may contaminate; biological discovery and mining may not be compatible. McKay asserts that “hitchhiking organisms” exposed to the martian environment are killed quickly by ultraviolet (UV) solar radiation but that bacteria inside spacecraft may survive and remain dormant because of the dry conditions. This theory does not account for the environments beneath the surface. Biological contamination from a crashed vehicle could be buried by the impact or deposited by Mars'winds in UV-shielded crevasses far from the crash site. A nighttime introduction would not expose bacteria to UV, allowing them time to work into cracks or other protected niches. Second, the surface may be dry, but the Phoenix Mars Lander found water ice at 5 cm below the surface. Should bacteria reach subsurface liquid water, they could propagate rapidly. Third, the Policy Forum states that contaminants “will remain local and static and can be removed without requiring an effort vastly larger than the missions that carried the contamination.” Such conclusions don't account for wind dispersal of contaminants not exposed to UV or possible burial by meteor strikes or landslides. “Biologically reversible exploration” (putting off cleaning up) may be impossible given experiences on Earth. Remediation is often extremely expensive, requiring political resolve. In Hawaii, for example, there is no effective control that is affordable and politically feasible for scores of alien species. If an invasive weed cannot be controlled in Hawaii [as in the case of Miconia calvescens , an invasive tree ([ 1 ][2])], what are the probabilities that a microbe on Mars can be contained and eradicated? How would costs be apportioned among space-faring nations? Lastly, McKay posits that discovering martian life “may open discussions of warming Mars to help that alien life to flourish.” Although it is true that warming generally speeds metabolism, it may be prudent to complete noninvasive studies of martian life processes and its evolutionary path and critique our motives for intervention first. While human-initiated warming of the planet may help humans, it would not necessarily “help” endemic life that has adapted to the present martian environment. If a goal of exploration is mineral extraction, early contamination, and plenty of it, would best justify a later conclusion that Mars is too contaminated to clean; exploitation with decreased regard for contamination would be facilitated. As industries gain a foothold on Mars, their influence on governance there will strengthen. If COSPAR requires clean Mars vehicles, the astrobiological value of a more pristine Mars would be enhanced. Now is the time for caution, while it is still an option. 1. [↵][3] 1. L. L. Loope , “Harmful non-indigenous species report: Report for Miconia calvescens” (Haleakala National Park Field Station, USGS/BRD, 1997). [1]: /lookup/doi/10.1126/science.1167987 [2]: #ref-1 [3]: #xref-ref-1-1 "View reference 1 in text"