Recently there’s been a load of exoplanet news talked about in various blogs. One thing that caught my eye though, was something about CO2 being discovered in the atmosphere of an exoplanet – HD 189733b. This planet’s atmosphere is full of it. Just like a glass of lemonade.
Needless to say, this is pretty exciting — if not for the chemical itself, but for the fact that we can now actually record a spectrum from an exoplanet’s atmosphere. In this case, they used the planet’s transit in front of it’s parent star — recording starlight passing directly through the planet’s atmosphere. Not an easy task, but an effective one.
Techniques like this definitely put us a step closer in the search for life, but… let’s not be getting ahead of ourselves here. What puzzles me is how they’ve decreed carbon dioxide as being a “potential fingerprint of life”. Carbon dioxide? Really?
It’s certainly true that most CO2 on Earth has a biological origin, but there seems little grounding for calling it a possible fingerprint of life. After all, the atmospheres of Venus and Mars are mainly composed of carbon dioxide and as far as we currently know, they aren’t exactly thriving oases. At least not in any manner we would immediately recognise. Titan too, has it’s fair share of carbon dioxide. Even Mercury has a trace amount of CO2. Water vapour too.
That said, it’s surprising seeing large amounts of CO2 in a giant planet’s atmosphere. HD 189733b is a hot Jupiter, but this discovery highlights the fact that it’s very different to our own Jupiter. One shouldn’t expect such planets to be too similar to the giants in our Solar System. This is, in every sense, an alien world. I’d be interested to know if they found any other molecules in it’s atmosphere too. I have a feeling these planets still have surprises in store for us.
Still, maybe CO2 shouldn’t be called a possible fingerprint of life. When someone finds some free molecular dioxygen, then I’ll be excited. O2 has only ever been seen in substantial quantities on Earth. It just too reactive to accumulate unless something’s creating it, and the thing that does that the best is life. If it were to be found anywhere else, it would be quite difficult to argue any cause other than life.
Thirst quenching image stolen from Kexi’s Photostream on Flickr.