Here’s an interesting question: Where will we find life outside Earth first? In our solar system, on worlds like Europa, Enceladus, Titan, or Mars; signs of it from an exoplanet; or possibly even signals from intelligent civilizations?
Science communicator Katrina Jackson sat down with two astrophysicists—my friends Michelle Thaller and Neil Gehrels—to talk about exoplanets and the search for life. It’s a short video but a very intriguing one.
(Note: This is one part of a longer conversation that covers more topics).
I wonder about this question as well (who doesn’t?). It’s a bit complicated, because we don’t know if life exists outside Earth in any of these ways. But for fun let’s assume it does. Which would happen first?
Right now, we’re not terribly well equipped to do a thorough search for life on worlds in our solar system. The rovers on Mars don’t have the right equipment to unequivocally detect signs of life. Anything they find short of macroscopic fossils would probably be indirect (say, chemicals in rocks indicative of biological processes). The evidence they find probably wouldn’t be conclusive either, so we’d be arguing for a long time over whether it was due to life or not. (This isn’t a guess; results from tests done by the Mars Viking landers are still argued over, and those tests were done in the 1970s.)
It’s the same problem for exoplanets. I’m excited about WFIRST, which is a proposed space telescope that can directly image exoplanets and get spectra of them (JWST will, too), which can detect the chemical signatures of elements and molecules in the atmospheres of the planets. If they find oxygen, that would be pretty spectacular! As Michelle says in the video, oxygen is highly reactive, and the best way we know to have it in an atmosphere at decent levels is through life. But as Neil points out, there may be things we don’t know, and the arguing will continue (and most likely justifiably so) even when the data are in hand.
As for SETI, they mention Seth Shostak, who has predicted that if intelligent life exists in the galaxy, and is broadcasting, we’ll find them in the next couple decades. It’s a bold prediction, based on current tech and our ability to improve our techniques. If we find a signal, what then? I wonder. If it’s a strong, clear signal (like in the movie Contact) then we’ll be pretty sure what’s what. But what if it’s weak, or noisy, or ambiguous in some way? We’ve had false hopes before (as Neil mentions in the video). It could very well be that what we find isn’t as clear as we hoped.
Because of all this, in the end, I’m not sure which way will produce the first, best results. And that’s assuming life is out there to begin with! The obvious solution is to keep looking in as many ways as we can. If life is out there, and it’s recognizable, it only makes sense to keep our eyes—and our minds—open.