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Southwest Research Institute scientist uncovers evidence of sub-surface ocean on one of Saturn's moons

Mimas, a small moon of Saturn

TPR's Jerry Clayton recently spoke with Dr. Alyssa Rhoden, who has uncovered evidence of a sub-surface ocean on one of Saturn's moons

Jerry Clayton: Based on data from the Cassini spacecraft mission, a Southwest Research Institute scientist has uncovered evidence of a liquid internal ocean on a tiny moon of Saturn called Mimas. Here to talk about her discovery is Dr. Alyssa Rhoden. Thanks for being here today.

Alyssa Rhoden: Sure.

Clayton: First of all, tell me about your research and how it led to this discovery

Rhoden: Several years ago there was a measurement made by the Cassini mission that led to a surprising paper where they said that Mimas, this tiny moon of Saturn, which looks like the Death Star, may have an ocean underneath its ice shell. And as someone who has studied ocean worlds for many years, I took one look at the images and I said, There ain't no way that that's an ocean world. And if you look at the surface, you'll see that it is not similar to the worlds like Europa and Enceladus that have young surfaces and many fractures. And so since then, I've been on a little bit of a crusade to dispute the Mimas ocean hypothesis and to prove that it could not be true. And eventually, I realized that that's not really the way scientists are supposed to work. We're supposed to come up with hypotheses and then test them. And so I made a list of all the ways, the things that must be true in order for us to have an ocean. And I started testing them one by one. And so this is the first results of those tests. So I tried to understand whether the amount of heat that would be generated in an ocean bearing Mimas was compatible with the thick ice shell that these Cassini measurements indicated.

Clayton: What is the possibility of these oceans containing some sort of life?

Rhoden: Well, that's always the big question, and one of the reasons that we're so fascinated with ocean worlds, we don't know yet because we haven't been able to explore the subsurface oceans on any of these worlds. So we're really limited in how we can explore. Luckily, NASA is investing in technologies and research to try to to access those oceans directly. And Enceladus, which is another moon of Saturn, Enceladus is erupting plumes of water that generate are generated in the ocean. And so there are mission concepts to fly through the plumes and collect that material to look for indications of life.

Clayton: How many worlds in our solar system have these subsurface oceans?

Rhoden: Ooh, that's a good question. And actually, we don't know the answer to that question. We don't have enough data. Many of the icy moons in the Outer Solar System. So as of today, I would say that we have three confirmed ocean worlds around Jupiter, and we have one confirmed ocean world, maybe two around Saturn. But there are many potential ocean worlds, places where we have small data sets or certain kinds of measurements that are consistent with an ocean. But we haven't been able to prove it yet. And when we go as far out as Uranus, Uranus has many icy moons and we simply have no data to really tell us whether those news are ocean bearing or not. And that's one of the reasons why Mimas is such an important target, because if a world that looks like Venus could be harboring this stealth ocean, then there are many other worlds that we've seen could also be ocean worlds.

Clayton: So what's next for the exploration of Mimas?

Rhoden: Well, you know, not many people have suggested we go explore Mimas because it looks like like a boring place or nothing really interesting is going on. But as we've learned more about the Saturn system, we've come to realize that Mimas may be formed fundamentally differently than other moons around other planets. So I think that it is an important target for me. I'm going to be thinking about its craters and its other surface features to try to understand this ocean a bit better. But a mission would definitely help if we could get new spacecraft data. There are more things that we could test.

Clayton: Dr. Alyssa Rhoden, congratulations on your discovery, and thanks so much for talking to us today.  

Rhoden: Of course. Thank you so much for having me.

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Jerry Clayton can be reached at jerry@tpr.org or on Twitter at @jerryclayton.