A shootoff from my other question, has there ever been a deep space probe that was not sterilized to prevent micro-organism contamination of the celestial body?

I'm thinking early space age history, starting with the Lunas and Pioneers attempting to hit the Moon in 1958. I consider myself well-read on Soviet space efforts (and American efforts too), but have never heard a peep about sterilization for either side.


1 Answer 1


The only spacecraft that I'm aware of that were fully sterilized were the Viking 1 and Viking 2 landers. They went through dry heat microbial reduction.

That page notes that some parts of the Beagle 2 lander were sterilized.

The MSL (Curiosity) drill bits and other components were sterilized, though the drill bits were later exposed to a clean-room environment without being re-sterilized. That turned out to be ok though, due to the nature of the selected landing site.

All other US Mars landers were simply cleaned and assayed to verify the bioburden limits (which are not zero).

Parts of the early Rangers (1-5) were sterilized and had gaseous treatments. They all failed, blamed in part on those processes. The direction was changed in 1962 to not apply either dry heat or gaseous sterilization to lunar probes.

It is difficult to know what exactly the Soviets did to Moon and Mars vehicles. This book describes some attempts to find out.

Gause assured Sagan that mission staff had sterilized Luna II’s instrument package and its third stage carrier rocket, both of which had impacted the Moon. But when pressed for details, Gause said some curious things, claiming “that his knowledge of the sterilization did not exceed that published in Izvestia." He said that the sterilization methods were those known to every graduate student in microbiology at the University of Chicago, and to every manufacturer of canned food, but he would not be more specific than that.

For Soviet Mars spacecraft:

Vashkov claimed that individual parts of landers were sterilized by heat (although he did not give the temperature or duration of the procedure) or by a radiation dose of 2.5 millirads, depending on the characteristics of the part. The landers were assembled in cleanrooms, and individual parts were carefully cleaned, probably with hydrogen peroxide. UV light was applied during assembly as an additional sterilant. Finally, before launch, Soviet mission personnel exposed the entire lander to a methyl bromide–ethylene oxide gas mixture for 6 hours at 50°C.

  • $\begingroup$ Thanks but this does not address, for example, the early Moon and Venera probes. $\endgroup$
    – DrZ214
    Commented Aug 18, 2015 at 20:36
  • $\begingroup$ You may have missed the use of the word "only" (in italics). There are no other spacecraft that were sterilized. $\endgroup$
    – Mark Adler
    Commented Aug 18, 2015 at 20:41
  • 1
    $\begingroup$ I didn't miss is, just as I didn't miss "that I'm aware of". Do you have a source saying all previous probes (lunas, veneras, rangers, etc) were not sterilized? $\endgroup$
    – DrZ214
    Commented Aug 18, 2015 at 20:46
  • 4
    $\begingroup$ Parts of the Rangers were sterilized (see update). Veneras certainly not. Venus does a far better job sterilizing our spacecraft than anything we puny humans might attempt. $\endgroup$
    – Mark Adler
    Commented Aug 18, 2015 at 21:44

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