Meteors Might Add Methane to Exoplanet Atmospheres

Meteoroids slamming against the atmospheres of alien worlds could add organic gases that make them look inhabited by life even if they are not, researchers say.

In recent years, astronomers have detected hundreds of extrasolar planets. Many of these exoplanets lie within habitable zones, the zones around their stars warm enough for liquid water to persist on a planet's surface, raising hopes that life as we know it might live on these distant worlds.

Ground-based observatories and proposed-but-cancelled spacecraft such as the European Space Agency's Darwin project or NASA's Terrestrial Planet Finder could scan the atmospheres of exoplanets for signs of extraterrestrial life. Molecules each absorb specific types of light, resulting in patterns known as spectra that allow scientists to identify what the molecules are. Some chemicals or combinations of chemicals might be unique to life as we know it, and could thus serve as strong evidence of aliens.

One key gas astrobiologists looking for extraterrestrial life would concentrate on would be oxygen, since researchers often think this molecule is too chemically reactive to remain for long in the atmosphere of a rocky planet like Earth without organisms to continuously produce it. Another possibility would be methane, a colorless, odorless, flammable organic gas that microbes on Earth produce. Seeing both together in an exoplanet's atmosphere might be an especially significant sign of life, since they would both ordinarily remove each other from the atmosphere without something like life to constantly replenish them.