False Signs of Life?

Well… chalk this one up as a bummer. It turns out that a method that was being used to determine whether an exoplanet was habitable has been debunked. This method, which was shown by NdGT on a recent episode of Cosmos basically works the following way:

Life on planets orbiting other stars doesn’t have to literally broadcast its existence: Radio signals are just one way earthbound scientists might detect biological activity elsewhere in the universe, says Hanno Rein, a planetary scientist at the University of Toronto, Scarborough, in Canada. Signs of life are much more likely to be subtle, especially if the organisms are simple. One way to look for such clues is to search for chemical evidence, particularly in light passing through the atmospheres of the planets, Rein says. By comparing the spectrum of light passing through an exoplanet’s atmosphere with that of the unfiltered light emitted by its parent star, astronomers can identify substances present in the exoplanet’s air.

Thus far, Rein notes, scientists haven’t been able to agree upon a single chemical—oxygen, for example—that could be a conclusive sign of extraterrestrial life. But researchers generally agree that certain mixes of two or more chemicals in an exoplanet atmosphere could be a strong sign of life, Rein explains. Here’s the idea: A mixture of gases that would normally react until one is completely gone simply can’t exist over the long term, unless one or both of the gases is being constantly replenished—possibly by the biological activity of life forms. One easy-to-understand example, Rein says, is a mix of methane and oxygen. Left to themselves, those two substances react to form carbon dioxide. And if life on Earth weren’t continuously producing those two gases, chemical reactions between the two would eventually scrub the less prevalent one from the atmosphere, leaving only the other.

It, of course, sounds good in theory. Of course, my question was always, “but if there are multiple chemical compounds, how can you determine if it contains all of them? Wouldn’t it just look like one solid spectrum of light?” Obviously, they’d found a way around this, probably because they’re scientists and I’m just a guy who’s interested in science.

Well… they did and they didn’t apparently. Again, according to the article on Science:

Now, Rein and his colleagues propose a scenario that could easily lead researchers looking for extraterrestrial life astray. What if, they say, a distant exoplanet has a moon with an atmosphere of its own? And furthermore, what if that “exomoon’s” atmosphere contains large amounts of a gas that would typically react with one from the exoplanet’s atmosphere if given a chance? Even if neither body hosted life, the combined light from the two objects might easily be mistaken as having passed through a single atmosphere of a body that hosts life, the researchers report online today in the Proceedings of the National Academy of Sciences.

So… multiple chemical signatures is screwing up their detection technique? I would really be interested to know how scientists had thought they’d mitigated this problem to begin with.

And this is what’s so frustrating about being stuck here on Earth, without a way to actually get out there and verify the results our instruments are bringing in. Firstly, our instruments can only look for what we tell them to. And, secondly, unfortunately we’re left to interpret the results based on our limited (but ever expanding!) knowledge of the world and universe around us.

I have crazy respect for the people that are analyzing this data and leveraging everything science knows about identification of planets based on their wobbles and makeup based on their light spectrums. It’s a daunting task. And we know way more about exoplanets now than when we did when I sat down and first started coming up with the URS. I also have crazy respect for the scientific community taking a step back and asking, “are we seeing what we’re actually seeing?”

What I’ll be curious to see is how they overcome this setback.

If anyone has any additional information on this method of planet observations, I’d love to hear about it. Maybe even as a guest post?