What might life on Europa look like?

Why do scientists think there might be life on Europa? And would it look the same as it does here on Earth? Here’s Adam Frank, a physicist and astronomer; and he should know, because he’s also the author of The Little Book of Aliens…

Adam - By aliens, we mean any life that has formed someplace else other than Earth. So, you know, microbes on Mars, the possibilities of animal life being evolved on alien planets, you know, distant exoplanets or the possibility of life forming in the ocean moons that orbit Jupiter and Saturn, which is what Europa is one of.

Chris - Why does Europa matter?

Adam - Well, so the important thing about Europa is it's a moon of Jupiter. It's a little bit smaller than our moon, but here's the amazing thing about it. When we sent space probes past Europa, what we found was there were virtually no craters on it, and there were no craters because it was ice. The entire planet was covered in a 10-mile thick layer of ice. And below that was a 100-mile thick ocean. So, Europa is a water world essentially, with a thick covering of ice in it. And there's more water on Europa than there is on earth by a factor of two, actually. So what that means is because we believe that water is essential, liquid water, for forming life, there may be other ways that it happens without water, but we really believe water is, you know, probably one of the best ways we can think of for life to form in that Europa is a great candidate for the possibilities of life in the subsurface ocean. And we can talk more about how that can happen, but that is really what it is. There's so much water that why this seems like a really great place for us to think about alien life forming.

Chris - Given it's millions of miles from the sun and most of the other entities around there are very, very cold. Why is there liquid water there at all?

Adam - Yeah, this is a really fascinating idea. It's because of what we call tidal forces, which really, you know, it's the same thing that's happening with the moon and the earth. Jupiter is huge and it exerts gravitational forces on the inside of Europa that heat it up. The gravity is constantly tugging and pulling and squeezing the inside of Europa, like silly putty, like just taking silly putty and squishing it back or clay and squishing it back and forth. It heats up and that heat is radiating out into the ocean, keeping the water from freezing. So it is this heat flow driven by Jupiter's gravity that's coming from the interior of Europa radiating out into its surrounding water that keeps the water liquid. And more than that, what we expect is there could be vents, places where molten rock is spewing up to the surface of the ocean. You know, the boundary between the rocky part of Europa and the liquid ocean and those deep sea vents are exactly the place where we think life could start. It's been hypothesised, that's how life started on earth, at deep sea vents in the earth's ocean. So that's really why we think life could have started on Europa. You know, billions of years ago, and maybe now Florida has evolved into a complex ecosystem.

Chris - Essentially that's like Darwin's warm little pools, isn't it? These hot springs. If that is the kind of environment with all the chemicals and raw materials arriving that might facilitate life, what's gonna power it though? What would life rely on for its energy source, if not that heat?

Adam - It would be the heat and the chemistry that is possible, in that heat. So, you know, you've got this upwelling of molten rock, which has all kinds of compounds in it already, sulphur and metals. And when they hit the water, all kinds of chemistry, as I like to call it, chemical shenanigans goes on. And that is a beautiful place to start powering biochemistry. And so you get biochemistry at these deep sea thermal vents, and then from that you can start evolving larger and more complex creatures. When we send deep sea probes down to these deep sea vents on earth, we find these amazing, crazy ecosystems of creatures we've never seen anywhere before, all living in the surroundings of those deep sea events. So they themselves can power rich ecosystems.

Chris - How are we going to investigate this though? Because given the scale that you've outlined for us, the amount of ice that's there, the huge volume of water that's there, and if all this is going on underneath all that, how are we going to see it?

Adam - Yeah, that's a great question. I mean, what you really want, the cool thing would be to land a nuclear powered heater that would just melt its way, through the 10 miles of ocean. But that's not going to happen any time soon because we don't know how to do it. So what we're going to do right now, at least how we're going to get started, is we're going to send a probe that's going to do flybys, multiple flybys around Europa, getting very close to its surface, and then turning a bunch of instruments at the surface. And what we can already see, is that the surface is a bunch of cracked plates of ice that are grinding up against each other. And on those cracks, those cracks actually have different colours than the surrounding ice because what we think is happening is at those cracks, you're getting liquid water from the ocean 10 miles below upwelling and making it all the way to the surface and refreezing.

Adam - And so that is new ice basically, that carries compounds from the water or from the, you know, from deeper in, you know, below the ice. And so by investigating the compounds we're going to find on the surface, we'll be able to tell whether those are the kinds of things we expect from life? Maybe we'll be even able to tell that there's stuff in those ridges that actually, you know, is life. I don't think we're going to be able to get there, but we're definitely going to be able to investigate these places where we think we're indirectly seeing water from the ocean.

Chris - What would be the hallmark then of life if you find particular traces or chemicals? What would be the ones that unequivocally say to a scientist that's a life process that produced that?

Adam - Yeah, that's a really interesting question, which people are going to argue about. I mean, to the first order, you kind of would love to find -proteins or something, you know, you would like to find large complex molecules that you think were indicative of being assembled, you know, by life. But even before that, you might just want to find, you know, even the building blocks of amino acids and things that are, because that would indicate that there were biochemical processes going on there. But you know, even as we've gone on, as we've become more sophisticated in our thinking about this, we're also thinking about things that life could be totally different. We shouldn't expect it's going to look like earth life. So people have been thinking about, like Sarah Walker and collaborators about the idea of agnostic signatures of life. Like just looking for molecules that are big enough and complex enough that we don't think nature without life could have produced them. So we are thinking about the possibility of how you would identify a molecule that looked very that came from a very different kind of life, but still something about its structure told you like only life could build something that big.