NASA’s Cassini probe has detected a thin layer of oxygen in the atmosphere of Dione, one of Saturn’s moons. Since scientist believe there to be no life on Dione, the presence of oxygen is perhaps even more interesting. Oxygen is highly reactive, enough to rust metal, for example, meaning that it bonds quickly to other elements. For this reason, scientists had thought that its sustained presence must be supported by living organisms, as on Earth, where plants continuously replenish the oxygen supplies in our atmosphere.
What’s the Big Idea?
Oxygen is one of the elements on the checklist for life on Earth, along with exposure to sunlight, access to water and manageable acidity levels. But even on Earth, there are animal species that stand radically outside this norm, such as microbes that survive on nutrients from deep ocean vents or the Bold Traveler bug, discovered in 2008, which survives without sun or oxygen in a gold mine a mile below the surface. It goes to show that further out in space, chemistry might change, allowing life to take on strange and wonderful forms.