We didn’t know, but along with Curiosity rover, NASA also sent bacteria to Mars. According to the tests before the launch, 377 strains of 65 bacteria species were detected.
Before the launch NASA scientist submitted the machinery to a rigorous cleaning, but despite that they found that many bacteria were still alive. The result, they are now on Mars, alive.
The scrubbing, scientist admit, could have been better, but the contamination is almost inevitable.
The problem with that is, in case of bacteria detection in future missions, scientist won’t be able to tell for sure if they are originated from earth or not.
As Nature News describes: “Most were related to the genus Bacillus. In the lab, scientists exposed the microbes to desiccation, UV exposure, cold and pH extremes. Nearly 11 percent 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.”
This study was presented for the first time to the American Society for Microbiology meeting in Boston.
But there is a problem, as Popular Cience describes :
“Scientists don’t want to contaminate other planets with Earth life forms. They also don’t want contamination in their own instruments, which could make it appear that they have detected alien life when they’re really only os ciêntistas vão usar esta informação futuramente para evitar contaminação measuring Earth-origin hitchhikers.”
Besides all this, scientists will use this new study to prevent future contamination in future missions.