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The space missions that aim to explore distant moons


Are we alone? It is one of the universe's biggest questions. And as my co-host, Mary Louise Kelly, found out, the answer could be in our own cosmic backyard.

MARY LOUISE KELLY, BYLINE: Saturn's largest moon, Titan, has long intrigued scientists with its rich stew of organic compounds, the building blocks of life. The moon has also captivated science-fiction writers.


KELLY: You can see its thick, orange atmosphere rolling off the USS Enterprise in "Star Trek."


KELLY: And Titan is the home world of Marvel supervillain Thanos.


JOSH BROLIN: (As Thanos) Titan was like most planets - too many mouths, not enough to go around.

KELLY: OK, but Titan is not the only moon that scientists are eager to explore. They also have their sights on the underground oceans of Jupiter's moon, Europa, and NASA has upcoming missions to both moons. Here to talk more about them are Catherine Neish, professor at Western University in Canada - she is on the team for NASA's Dragonfly mission; it's going to head to Titan in 2028 - and Kevin Hand, who directs the Ocean Worlds Lab at NASA's Jet Propulsion Laboratory in Pasadena. He is also working on Dragonfly and the Europa Clipper spacecraft, which is blasting off in October. Welcome to you both.

CATHERINE NEISH: Hi. Great to be here.

KEVIN HAND: Thank you.

KELLY: Kevin, I'm going to let you kick us off with this mission to Europa since that is coming right up in the fall. This moon has a salty ocean that is locked under a shell of ice. Describe it. What else can you tell me about it?

HAND: Yeah. That's right, Mary Louise. Europa has this ocean of salty liquid water beneath this ice shell that's about maybe 10 or so kilometers in thickness. We really don't know. And if we've learned anything from life on Earth, it's that, where you find the liquid water, you generally find life. And so worlds like Europa and that harbor liquid water oceans out there in our solar system today - these worlds are incredibly compelling from the standpoint of our search for life beyond Earth.

KELLY: Even if they're under - you just described kilometers of ice on top. That's a lot of ice.

HAND: That's right. These are dark oceans, and so photosynthesis as we know it here on the surface of the Earth is probably not really a viable energy pathway. Instead, if there is life in these oceans, it's probably sustained through chemical reactions that can power life - similar, perhaps, to what we see in the deep, dark depths of our own ocean - places like hydrothermal vents where microbes and other organisms just chew away night and day without any knowledge of the sun above.

KELLY: And one more to you, Kevin, because I'm told engineers have just finished loading the scientific instruments onto the Europa Clipper in preparation to launch. What, specifically, are y'all going to be looking for? You get there in 2030 - is that right?

HAND: Yeah, about that time frame. It launches - knock on wood - in October. And once the spacecraft is there, the payload is designed to assess the habitability of Europa. It'll have cameras that can take images of the surface, spectrometers to tell us about the chemistry of the surface and any materials coming off of the moon. And then we've also got an ice-penetrating radar that will allow us to see within the ice and potentially even to the ocean below.

KELLY: OK, Catherine, jump in here because I want to turn to this other really intriguing moon. This is Titan, Saturn's moon. It might also have a subsurface water ocean like Europa, but I'm told it also has seas of liquid hydrocarbons - things like methane on the surface. Help me picture that.

NEISH: That's right. Titan is unlike any icy world in the outer solar system because, unlike most icy worlds, it has an atmosphere - an atmosphere that's not dissimilar to Earth's, made primarily of nitrogen, but it also has methane. And at the low temperatures that we find on Titan, that methane can actually act as a liquid. So we see lakes. We see streams. We see all the same erosional patterns we see on Earth. It's just the materials are all different.

KELLY: Hmm. So the Dragonfly mission, which, I gather, if all goes well, will arrive and start hopscotching around the surface of Titan in the mid-2030s - what are you hoping specifically to learn?

NEISH: One thing we think is happening on Titan is that the organics that are formed in its atmosphere because of the presence of nitrogen and methane rain down on the surface. And then once they're on the surface, they can mix with these transient liquid water environments we think are there in the bottom of impact craters. And if you mix those two ingredients - carbon-containing compounds and water - that's very similar to what we think the origins of life looked like on Earth. So we're really hoping to see maybe the starting point of life happening on the surface of Titan, which we can then sample with Dragonfly.

KELLY: So this prompts a question to both of you because you've both been describing on two different moons conditions that possibly could support life, but it sounds like very different conditions - totally different than we have here on Earth. Does that mean there's the possibility that these seas would support life as we don't know it - life that looks nothing like what we would recognize as life here on Earth?

NEISH: So that's certainly true for the methane oceans on Titan. If there is any life there, it is going to be completely different than what we see on Earth because, unlike life on Earth, which uses water as a solvent, if there was life in the oceans on Titan, that would use methane as a solvent - so completely different. And I'm not even sure we're clever enough to search for that life. It would be so alien to us.

KELLY: That's the thing. Like, would we even know if we found it if it looks so different?

NEISH: That is a concern of mine, for sure.

KELLY: Kevin, what do you think? Life as we know it, life as we don't know it - would we even know it if we find it?

HAND: Yeah. Well, part of the way that these spacecraft and the instrument payloads are designed is to have the opportunity for discovery-driven science - finding things that we can't really predict are out there. And Titan is just such a wonderful world in this context because, like Catherine said, it's a great place for life unlike life as we know it.

KELLY: I mean, I suppose this prompts me to ask how hopeful either of you are. My editor's here reminding me that we've been hunting for life elsewhere in the solar system for decades. They were reminding me back in the 1970s - the Viking 1 and 2 missions landing on Mars. Has - have all of the intervening years tempered your expectations at all about our ability to find life elsewhere in the solar system? Kevin, you first.

HAND: Well, I guess, first, I'll say this business is not for the faint of heart. It's a generational endeavor. And while we have been exploring the solar system for roughly 60 years or so, we really have not sent that many spacecraft beyond the asteroid belt. And so this type of exploration is really just beginning.

KELLY: Catherine?

NEISH: I think if we're going to find life anywhere, it's going to be within our own solar system, and this is the whole reason I became a planetary scientist. However, in the 20 years I've been in this field, I think I've become a little bit more pessimistic about our options here. And that's because, in addition to water, which Kevin has brought up, life also needs carbon. And in so many places in the solar system, we find one or the other, but not both. So we really need to focus on those areas where we have all the ingredients you need for life together in the same environment. And I'm hopeful we can find those environments, but I think they're not as numerous as I originally hoped.

KELLY: We'll leave it there, on a note of cautious optimism. That is Catherine Neish of Western University in Canada and Kevin Hand, director of JPL's Ocean Worlds Lab. Thanks so much to you both.

NEISH: Thank you so much.

HAND: Thank you.

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Kai McNamee
[Copyright 2024 NPR]
Christopher Intagliata is an editor at All Things Considered, where he writes news and edits interviews with politicians, musicians, restaurant owners, scientists and many of the other voices heard on the air.
Mary Louise Kelly is a co-host of All Things Considered, NPR's award-winning afternoon newsmagazine.