AILSA CHANG, HOST:
Almost 20 years ago, a school bus-sized spacecraft called Cassini was sent from Earth to Saturn. Its journey ends tomorrow when it plunges on a suicide mission of sorts directly into Saturn itself. Cassini is going out in such a dramatic fashion because we now know that two moons of Saturn might contain life. And if Cassini were allowed to become floating space junk, it could crash into one of those moons one day and possibly jeopardize that life if it exists.
To talk about what we know now about these moons thanks to the Cassini mission is Jonathan Lunine. He's a member of the Cassini science team and director of the Cornell Center for Astrophysics and Planetary Science. Welcome.
JONATHAN LUNINE: Thank you, Ailsa. It's a pleasure to be here.
CHANG: Thanks for joining us. So you were at the very first meeting about the Cassini mission, right? We're talking almost 30 years ago, right?
LUNINE: That's right.
CHANG: And back then was there any inkling that there could be life on these two moons, Titan and Enceladus?
LUNINE: No, there wasn't. All we knew about Enceladus was that it was very bright and icy and perhaps had some kind of geologic activity. And Titan we knew very, very little about.
CHANG: So what did Cassini see? I mean, what do these two moons look like?
LUNINE: At Enceladus, Cassini saw these very, very long fractures that cut through the South Pole. And at close examination, those fractures have other fractures branching out from them with gas and ice pouring out of all of these. So it's very, very active. Titan, if you look at it with the eye, just looks like an orange ball. It's covered in a haze that's caused by the chemistry involving methane in the atmosphere. But in the equator there's a belt of dunes. And then near the poles - at the north polar region, there's this complex of lakes and seas. So it's quite a complex and intricate surface.
CHANG: It sounds almost idyllic.
LUNINE: Except it's so cold.
LUNINE: Minus 290 Fahrenheit is not all that idyllic.
CHANG: No, that doesn't sound very comfortable at all. And when we say life, can you help me picture what we're talking about here? Like, this isn't little green men, right (laughter)?
LUNINE: This is almost certainly not little green men or, in the case of Titan, little orange men.
CHANG: Uh-huh (ph).
LUNINE: In both cases, if there is life, it's primitive life, single-celled life - what a biologist would call microbes.
CHANG: But is there a possibility that these microbes - if they exist, could they evolve and develop into advanced forms of life eons from now, like creatures with eyeballs and language?
LUNINE: So the limiting factor here is really sunlight. In the case of Enceladus, life would be in the ocean underneath the icy crust where it doesn't have any access to sunlight.
LUNINE: And it's really sunlight and photosynthesis that made it possible for complex life to evolve on the Earth.
CHANG: And why do we think Titan might also have life on it?
LUNINE: So Titan is a different story. It also has an ocean detected by Cassini. But of even more interest is that on the surface of Titan are lakes and seas of liquid methane.
LUNINE: And one of them is as large as the Caspian Sea on the Earth and - now, we don't know if a form of life can exist in liquid methane. Of course, we depend on liquid water. So if there is life in those seas, it's something that's very, very exotic.
CHANG: This mission has been part of your life for almost 30 years. How does it feel to see it coming to an end now?
LUNINE: It's very difficult. Up until yesterday, actually, my response was, well, we've had such a tremendous success with this mission and the science that it's generated will carry us forward for years to come. But I have to say that today I feel very sad because we're on the threshold of a tomorrow when there will not be a Cassini mission to make new discoveries. And while I know there will be future missions, this one has been just an extraordinary odyssey of exploration. And just to be on the day that you have to say goodbye to it, that is a day that for me is very sad.
CHANG: Jonathan Lunine has been a member of the team behind the Cassini spacecraft mission to Saturn. Thank you for speaking with us.
LUNINE: Thank you, Ailsa.
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