We’ve sent these germs to Mars.

And now, Nature says, we know the names of the interplanetary stowaways:

Swabs of Curiosity’s surfaces before it was launched, including its heat shield and flight system, revealed 65 species of bacteria. Most were related to the genus Bacillus. In the lab, scientists exposed the microbes to desiccation, UV exposure, cold and pH extremes. Nearly 11% of the 377 strains survived more than one of these severe conditions. Thirty-one per cent of the resistant bacteria did not form tough, protective spore coats; the researchers suspect that they used other biochemical means of protection, such as metabolic changes.

The data presented by [University of Idaho microbiologist Stephanie] Smith and her team may help mission scientists to evaluate cleaning procedures. The data also indicate a need for more research on planetary protection, according to Smith. Knowing which species might stow away on space missions could be critical for a planned 2020 NASA mission that will use a rover almost identical to Curiosity to bring samples of Martian soil and rock back to Earth.

“This can keep us from identifying dead bugs from a sample return mission as something that originated on Mars,” says Rummel. “We could be sure that they’re not Martians.”