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Before a rover or other exploration vehicle is launched, it undergoes rigorous cleaning and disinfection, such as a bath in UV rays to kill off bacteria.

The official reasoning on this seems to be that the bacteria on the vehicle (deposited by people touching it, spiders on the ceiling, whatever), may cause a false positive for life on the other planet by "riding" the vehicle to space and leaving the vehicle for the other planet. There, it would colonize. We would later detect it and say that it's a sign that life exists there.

However, my understanding of this answer is that cosmic radiation will take care of it on its long journey:

It appears that most of the true sterilization actually takes place after launch. The harsh conditions of the trip there and the landing should be enough to kill off a majority of the microbes.

The Mars rover projects all receive multiple sterilization treatments here on Earth before launch, typically UV treatment, but what really kills off the bacteria is the exposure to cosmic radiation on the trip over and the intense UV radiation on Mars' surface.

If cosmic radiation will kill it all off anyway, what is the real risk to leaving life on a spacecraft headed for another planet?

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  • $\begingroup$ It looks like NASA goes to town then it comes to this process of disinfecting before hand. planetaryprotection.nasa.gov/methods $\endgroup$ – John Riselvato Jul 21 '13 at 8:07
  • $\begingroup$ @Undo: The statement that the harsh conditions in space will do is just not true. I gave another answer to the very same question, you are referring to. There are a few links in this answer. I would advice you to read them (this includes the sources of the wikipedia articles, btw). $\endgroup$ – s-m-e Jul 21 '13 at 14:54
  • $\begingroup$ @ernestopheles Neat! Learned a lot from that answer $\endgroup$ – Undo Jul 21 '13 at 14:57
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I do know that the Deinococcus has the ability survive in high energy levels of radiation which is an earth bacteria. Chances are they are just trying to limit chances of something going into space alive. Anything is possible and it also would just seem careless to send earth life into space. This is especially true knowing that thermal adaptation in bacteria is possible.

The Deinococcus radiodurans seems like the perfect bacteria to ensure you're not taking with you to space:

radiodurans is a gram-positive, red-pigmented bacterium that typically grows in a tetrad structure. It is a nonsporulating and strictly aerobic bacterium, but it has been known to survive in vacuum conditions. D. radiodurans is a chemoorganotroph with an optimal growth temperature of 25º – 35º C; however, it is very resistant to extreme temperatures. The bacterium has been isolated from numerous locations, including elephant dung and the granite of Antarctica’s dry valleys. The natural habitat has not been determined.

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  • $\begingroup$ "Anything is possible and it also would just seem careless to send earth life into space." That's the point!!! $\endgroup$ – s-m-e Jul 21 '13 at 14:50
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Currently the majority of interplanetary travel is funded by government, government is maintained by politics, politics are governed by politicians, politicians are governed by... (well I am not sure, but in any case that would be out of scope for this site)

Obviously a purely scientific mission searching for life would want to observe good hygiene, and ensuring your vehicle is clean before it leaves ensures that anything it finds is new.

Filling your vehicle with all the known bacteria of the world and seeing how it survives when exposed to cosmic radiation is a test that I don't believe has actually be conducted yet.

But lastly, even if you transfer dead organisms to Mars, when you find a dead organism on Mars there is no way to know its origin. If you can find dead organisms on mars that did not have terrestrial origins that you have proven extraterrestrial life does or has existed. As we don't have proof of extraterrestrial life, nor a method for categorizing life as clearly terrestrial in origin, these questions remain important so the precautions remain necessary, from a scientific perspective.

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