A spore is a bacterium's survival capsule: dried almost solid and wrapped in protein armor, with its chemical processes shut down. Bacteria enter this state of hibernation when environmental conditions are unfavorable. What's left is close to indestructible: It can survive boiling, desiccation, radiation and the vacuum of space. NASA once bolted Bacillus spores to the outside of a satellite and left them in orbit for nearly six years; the ones shielded from sunlight were able to come back to life upon returning to Earth.