Which planets and moons have we accidentally (or purposely) seeded with life? I would expect this to be any planet or moon we have sent an unsterilized (or not fully sterilized) lander to, or crashed anything into.

I am speaking largely of bacteria and other microorganisms that might have hitched a ride on our spacecraft, or any life that was deliberately taken to and left on another world (which I am not aware). I know we went to the moon, we at the very least "seeded the moon" temporarily with life (humans) and probably bacteria on the space suits / lander / equipment we sent.

I wondering where we have "seeded" / brought life (even if it doesn't / didn't survive there).

  • 1
    $\begingroup$ The question would seem to imply that "seeding" is sufficient, even if the body in question contains no medium in which any terrestrial life could possibly grow. Or am I missing something? $\endgroup$
    – Donald.McLean
    Mar 2 '16 at 19:02
  • $\begingroup$ Yes, that is what I am asking about, where we have actually sent life (not whether or not it will actually grow there). $\endgroup$
    – Jonathan
    Mar 2 '16 at 19:40
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    $\begingroup$ As I understand it, it's very difficult to completely sterilize (as in, kill every last microbe), on a spacecraft, though NASA and most nations that launch space craft have made an effort to address this concern. en.wikipedia.org/wiki/Planetary_protection $\endgroup$
    – userLTK
    Mar 2 '16 at 20:13
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    $\begingroup$ Space craft are not the only possible vectors for biological contamination of other bodies within the Solar System. For some idea of transfer of surface material between terrestrial planets see this abstract $\endgroup$ Mar 3 '16 at 11:19

This would seem to be constrained to planets and moons earth has landed on or impacted at all, as we have no way of telling after the fact whether a lander was perfectly sterilized. That list is as follows:


  • Mercury: USA's MESSENGER in 2015 de-orbited and crashed upon completion of mission. Contamination is unlikely because of high impact and temperatures.

  • Venus: 13 missions by the USSR and 1 by the USA (1966-1985). Contamination unlikely due to harsh environment.

  • Mars: 12 missions, multi-national origins. Contamination plausible.

  • Jupiter: The Galileo missions (2), by the USA Contamination unlikely, because of pressure.


  • Earth's moon: Far too many to count, myriad landings. Contamination plausible.

  • Saturn's moon Titan: Huygens probe, landed by the ESA (2005) Contamination Plausible.



My best guess (though I don't know about every mission) is that we have at least seeded our moon with life when we visited it. We have also likely seeded Venus, Mars, and Jupiter with the various probes we have sent to each. As far as I know, we have only done flybys or put probes in orbit for the other planets and moons, so they have likely not been seeded yet. I would like clarification / confirmation, and other possible locations. I know we now generally sterilize our probes, but the procedure could be incomplete, and I don't believe we have always sterilized them in the past.

  • 2
    $\begingroup$ "sterilize" is not a single thing. Depending on the level of risk that contamination would have, craft would be cleaned to a greater or lesser degree. $\endgroup$
    – BowlOfRed
    Mar 2 '16 at 21:30
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    $\begingroup$ You may be able to refine your answer by studying NASA's planetary protection website: planetaryprotection.nasa.gov/missions $\endgroup$
    – Gerald
    Mar 2 '16 at 22:13

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