MICHELLE THALLER: So, Stephanie, you ask a great question: How likely is it that we're going to find life on a planet outside the Earth in your lifetime, say in the next 40 or 50 years? And, of course, this is something that nobody can answer exactly. "We don't know," that's the answer. But I think it's very likely indeed. Now, when I say life, there's a lot of ways you can take that word. I'm not really talking about civilizations or spaceships or things like that; I think it's much more likely that we're going to find microbes, simple life—but to me, that would be really, really exciting. There are several places in our own solar system right now that we think might be good environments for life. And, as I said before, we haven't found proof of life yet, but we found some very, very interesting things. For example, on Mars—Mars has an atmosphere that's much thinner than the Earth's, but it is still there; we think there might even be water underneath the surface of Mars. And recently we've detected organic molecules, which are sort of the building blocks of our chemistry, on Mars as well. It's possible that the surface of Mars itself is not a very good place for life, but maybe underneath, meters under the soil in the rock you could find bacteria. And there a lot of analogs to this on Earth, similar things on Earth. We find bacteria that can exist a mile under the Earth, we find these things in gold mines very, very deep under the Earth. You break open the rocks and there's actually bacteria living in the rocks very far down into the Earth.

There are other places in the outer solar system that we think are great environments for life, too. There are moons of Jupiter and Saturn that we know have liquid water oceans. For example, Europa is a moon of Jupiter and we know that Europa has vast reservoirs of liquid water that are protected by a shell of ice. In fact, this one moon of Jupiter, Europa, actually has far more liquid water on it than Earth does. And there are some suggestions that there might be interesting chemistry as well. There's also a moon of Saturn called Enceladus. And the same thing applies: There's liquid water under ice. And in the case of Enceladus, you actually have cracks in the ice that the water is flying out of and turning into ice crystals. We actually flew our Cassini spacecraft through these jets coming out of Enceladus and we detected organic molecules, so we know that there is warm salt water, there's interesting chemistry—it's a great place to go looking for life. And there's another moon of Saturn too, called Titan, which is very different from that; it has an atmosphere. We actually think that there are lakes of methane, not water but actually liquid methane on the surface. And below that, there's probably liquid water underneath. So you have liquid water, you have organics, you have an atmosphere—maybe that would be a great place to go looking for some microbes.

So some people say that's not very exciting; we're not going to find aliens in the sense of spaceships and Klingons and any science fiction you want. I, for one, though, I'm going to be very excited when we find any evidence of life outside the Earth. I actually have a bottle of champagne chilling because I think it could happen almost any day when some of our rovers or some of our satellites around other planets come back with really interesting data. Think about the questions we can answer: Does life, even if it's at a bacterial level, even if it's just a tiny little bit of life, does it have DNA? Is it similar to us? Is it different from us? We finally have the next example of how life can form and how life can evolve, and our view of the universe will never be the same again. And my bet is that's going to happen in the next 50 years.