It’s generally been believed living organisms can’t survive the cold vacuum of space. But recently, astronauts discovered living bacteria outside the International Space Station. Taken from swabs, the bacteria was absent during the launch of the module. It’s led some to claim it’s the first proof of alien life, but the astronauts think there’s a likelier explanation. Rising air currents can carry the bacteria up into Earth’s upper atmosphere, where it can cling to the spacecraft.