Hubble finds methane on exoplanet; later, methane==life

Tomorrow Nature will publish an article where Mark R. Swain, Gautam Vasisht, and Giovanna Tinetti explain how they were able to tease out a discovery of methane in the atmosphere of HD 189733b using Hubble. In and of itself, the discovery is great, but what the discover portends is much more fantastic.

When I talk to people about my work in astronomy, often the subject of life on other planets comes up, and I am quick to tell them that evidence of life will be discovered on another planet in our lifetime, and probably in the next couple of decades. They are both intrigued and disappointed when I explain that we will find chemical signatures of life, and not intelligent aliens waving back at us (that, unfortunately, won't happen before my time is up on this pale blue dot.)

This discovery gets us that much closer to finding this chemical evidence of life. Methane specifically is interesting, because in an oxygen rich atmosphere, methane along with sunlight breaks down in millions of years. That might seem like a long time, but for the lifetime of planets, it is pretty small. So, when we find methane in an oxygen rich atmosphere, we know that it is being replenished at least every few million of years. One of the big, regular sources of methane on the Earth are animals and decomposing plant matter. This particular planet, HD 189733b, is a gas giant and much too hot for any type of familiar life, but if we can detect methane on this planet, we can eventually detect methane on smaller, more hospitable planets.

In an article in the New York Times on the discovery, Sara Seager, one of my Ph.D. supervisors, suggests that Hubble, though quite remarkable, wasn't built with exoplanets in mind, and that the next generation of space telescopes will add exponentially to our understanding of these extrasolar planets, and specifically Earth sized planets. She really hit the nail on the head. An entire generation of astronomers is currently searching for planets, mainly because of the possibility of finding an Earth analogue. Sure, many astronomers are searching for Hot Jupiters now, but I think all of them would admit that what really interests them is finding Earth-type planets, and specifically life on other planets. This discovery of methane brings us one step closer towards that ultimate goal of finding life.