Our Best Bet to Find Alien Life May Be 'Biosignature' Gases
Finding alien life isn't an exact science yet—unless we stumble upon microbes on Mars or get a visit from a real-life Klaatu and Gort, astronomers are left staring at planets and saying "Well, there's a better than average chance there's life on that rock, maybe." We've already found two exoplanets that might be havens for life (at least one may have an ocean of liquid water!), but scientists have come up with a new tool to find alien life that may narrow it down.
Researchers from the University of Washington have looked back in Earth's 4.5-billion-year history and found that there were a handful of gases—known as "biosignature gases"—that were vital to the development of microbial life. Oxygen, of course, is the major one, but it's not essential. Instead, the researchers found that "methane, carbon dioxide and a lack of carbon monoxide" may be the right cocktail of gases to cultivate life:
"Methane can be produced by asteroid impacts, emissions from the inside a planet itself and reactions of rocks and water. However, the team think it is unlikely an Earth-like planet could produce large amounts of methane without life as well. Processes such as volcanic eruptions spew out carbon monoxide as well as carbon dioxide and methane. Microbes love to munch on carbon monoxide, so—if they exist on a planet—there shouldn't be much of the gas left at all."
The cool part about using these gases to identify life-harboring planets is that it's feasible (it doesn't require huge leaps in technology to start using the method) and that it can combine with what we already know about habitable exoplanets: the check-list used to be "is this planet the same distance from its star as the Earth is from the sun?" but now we have a whole host of criteria based on temperature, planet composition, orbit, and now atmospheres.
Even if we don't find a planet that already harbors alien life, we might be able to start finding planets that will one day harbor human colonies. And we won't even have to nuke the planets to terraform them.