Just before going off on paternity leave (see previous post) my eye was caught by a "Cross-talk" column in the Lancet Infectious Diseases, in which Bernard Dixon talks around this. He refers to work that was done looking for microbes in the clean rooms at the Jet Propulsion Laboratory in California and at the Johnson Space Center in Houston. Samples were examined for evidence of Archaea, and evidence was found.
Dixon suggests that the question had been raised before of whether microbes from Earth could hitch a lift into space, and that there are protocols to try and prevent them doing so. But if Archaea can survive in clean rooms, should instruments and so on on spacecraft bound for Mars be screened for them? If microbes are found on Mars, how will we know that they didn't come originally from Earth?
The Lancet Infectious Diseases article is:
Dixon B. Spacebugs. Lancet Infectious Diseases. 2008; 8(8): 466. DOI: 10.1016/S1473-3099(08)70165-8
I've been following the Mars Phoenix Lander via Twitter - http://twitter.com/MarsPhoenix