Q. Are any microbes hardy enough to survive in outer space?

A. Experiments have found that many microbes survive and even thrive in a space-vessel environment. But most do much worse when exposed to some of the actual conditions of outer space, either in the laboratory or in space, according to an extensive review of space microbiology, published in 2010 in the journal Microbiology and Molecular Biology Reviews.

Of all the organisms tested, only some lichens, Rhizocarpon geographicum and Xanthoria elegans, were fully viable after two weeks in outer space, with its radiation, vacuum, temperature extremes and low gravity. The most harmful factor, the reviewed studies concluded, was the high level of solar ultraviolet radiation found beyond the ozone layer.

However, if spores of Bacillus subtilis, a common bacterium, were shielded against the radiation, they did survive in space for up to six years, especially if they were embedded in clay or in artificial meteorites made of meteorite powder.

These findings support the possibility of interplanetary transfer of microorganisms within meteorites, the review concluded.