Don’t bother to sterilize space craft

One of the reasons people are so interested in Mars is that it might once have harbored life. It’s even possible that life exists there today, somewhere under the surface. If we do ever find signs of life on Mars, we’ll want to know whether it originated on that planet, rather than being the result of contamination from Earth. To make that distinction, astrobiologists on Earth have been trying their best to sterilize everything we send into space. However, Alberto Fairén of Cornell University and Dirk Schulze-Makuch of Washington State University think we shouldn’t bother. In all likelihood, Mars has already been contaminated with Earth species.

We know that Earthly bacteria could survive the journey through space and land intact on Mars. This makes it seem to be critical to sanitize everything we send out that way, until you consider two things. First, it would be impractical, not to say impossible, to ensure that no Earth microbes found their way en route to Mars. Second, even if we did make that extra effort going forward, earlier Mars missions have already landed an assortment of completely unsterilized objects on the surface of Mars. And that doesn’t even count the nearly 4 billion year history of possible meteorite transfer of life forms from Earth to Mars. 

In short, if Earthly life can thrive on Mars, it’s there already.

The authors argue that either present day Earth species cannot survive on Mars, in which case there is no need for pre-flight sterilization, or Earth species can survive on Mars, in which case they’re already there so there’s still no need for sterilization. In the first scenario, decontamination is unnecessary and in the second it’s too late to do any good. 

Even if there is indigenous life on Mars that isn’t related at all to Earth species, these two scenarios still hold. Martian species won’t be affected by Earth species that die upon arrival, and Martian species must have already adapted to Earth species that can thrive on Mars.

According to Fairén and Schulze-Makuch, if there is a reason to sterilize outgoing space craft, it’s to make the job of distinguishing Earth from Martian species easier, a task we may never be faced with. They contend that, given the limited budget for Mars missions, the money be reallocated to more important tasks. 


Alberto Fairén, & Dirk Schulze-Makuch (2013). The overprotection of Mars Nature Geoscience DOI: 10.1038/ngeo1866.