Reports of Streptococcus mitis on the moon

It is widely claimed that a common bacterium from the human mouth, Streptococcus mitis, survived for two and a half years on the Moon inside the Surveyor 3 camera, to be detected when the camera was returned to Earth on board the Apollo 12 capsule. However, this claim cannot be sustained in the light of several lines of evidence:

• Streptococcus mitis lives in the mouth; there is no evidence that it can survive for long even in terrestrial environments outside the human body.
• Streptococcus mitis, like other oral streptococci, is a mesophile; it cannot survive outside of a narrow temperature range centered on human body temperature. It is not an extremophile nor does it produce endospores. It could not survive on the moon.
• Even extremophiles are unlikely to survive the extremes of temperature on the surface of the Moon (mean surface temperature day 107°C; mean surface temperature night -153°). Surveyor 3 would have gone through over thirty day-night cycles on the Moon, each one provoking freeze-thawing of bacteria. Applying multiple cycles of freeze-thawing is a commonly used technique for breaking open bacterial cells.
• There is evidence to suggest that the camera was contaminated after return to Earth [1]. Leonard D. Jaffe, who was Surveyor program scientist and custodian of the Surveyor 3 parts brought back from the Moon, wrote to the Planetary Society stating that somebody on his staff, who had witnessed the biological test which gave positive results, reported that a "breach of sterile procedure" took place at just the right time to produce a false positive result. One of the implements being used to scrape samples off the Surveyor parts was laid down on a non-sterile laboratory bench, and then was used to collect surface samples for culturing. It was that sample set which showed the presence of Streptococcus mitis. To quote Jaffe, 'It is, therefore, quite possible that the microorganisms were transferred to the camera after its return to Earth, and that they had never been to the Moon."
• The Surveyor 3 camera was returned from the Moon in a nylon duffel bag, and was not in the type of sealed airtight metal container used to return lunar samples in the early Apollo missions. It is therefore possible that it was contaminated by the astronauts in the Apollo 12 capsule itself.
• The test for recovery of bacteria could only be performed once, and the parts were subsequently taken out of quarantine and fully re-exposed to terrestrial conditions (the Surveyor 3 camera is now on display in the Smithsonian Air and Space Museum in Washington, D.C.).

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On the above evidence, the most parsimonious explanation for the reported recovery of Streptococcus mitis from the Surveyor 3 camera is contamination after its recovery from the Moon. Survival of this bacterium on the surface of the Moon would be very unlikely. This claim has never been documented in any peer-reviewed scientific publication and remains a telling example of the phenomenon of urban myth.

NASA is funding an archival study in 2007 that will try to locate the film of the camera-body microbial sampling to confirm the report of a breach in sterile technique.