Ask the Astronaut: Could an astronaut on Mars affect the planet’s evolution?

A Viking lander of the 1970s being prepared for sterilization in an oven.

Q: If an astronaut happens to bleed on the soil of Mars or other planets, will it affect the planet’s evolution? (Saman Ratna Buddhacharya, Kathmandu, Nepal)

Planetary scientists and mission design engineers planning for robotic and human missions to Mars must protect the Martian environment from Earthly contamination. That means we should not deliver Earth microbes and biological materials to Mars’ surface, lest they interfere with later searches for life there. Imagine announcing a finding of life on Mars, only to learn later your Mars bacterium was in fact a germ from Earth that hitched a ride on your own spacecraft, ruining a mission costing hundreds of millions of dollars.

To prevent such contamination, NASA has a planetary protection office, which sets stringent standards for spacecraft headed for Mars or other planets. The most stringent standards are applied to spacecraft searching for life, like the two 1970s-era Viking Mars landers. Those craft required a “full system sterilization”—the landers were packaged and put inside a bioshield and baked in an oven to kill all microorganisms. The landers were heat-treated for 30 hours at 125° C, long enough to reduce the bacterial count by a million-fold. The landers stayed within the bioshield container until they reached Mars orbit, preventing recontamination. Landers without life-detection instruments don’t require baking, but they are chemically sterilized, and the surfaces are sampled and analyzed to ensure few microorganisms will arrive on Mars (where the harsh environment will kill most of them).

Humans, of course, travel with their own zoo of microorganisms, and shed them everywhere they go. Whether it’s blood, germs, or viruses, contamination from a human expedition will be inevitable. The best searches for life will probably be done by sterile, human-controlled robots far from the astronaut habitat. Because the Mars surface is so hostile to life, though, astronaut contamination will probably not affect any genuine Mars life—which is likely to live below the surface in a warmer, wetter environment. If we can find it, we’ll try to study it with special care to avoid confusing it with Earth organisms.

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