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Oceans May Lurk Inside Saturn’s ‘Death Star’ Moon

It’s a moon… and a submerged ice ball?

With a large crater carved into its surface, Mimas, Saturn’s 250-mile-wide moon, bears many similarities to the Death Star from “Star Wars”. (When the Millennium Falcon first encountered the Death Star, Obi-Wan Kenobi said ominously, “It’s not the moon. It’s a space station.”)

For eight years, scientists have considered that Mimas, seemingly a pockmarked ball of frozen ice, may be hiding a secret: an ocean that flows 14 to 20 miles below the surface .

In recent years, such ocean world – Europa at Jupiter and Enceladus at Saturn, name two – jumped to the top of the list for scientists looking at places in the solar system where life could arise. One NASA’s spacecraft, Juno, will pass through Europa for a closer look this year, and another mission, the Europa Clipper, will arrive on a dedicated mission there in 2030.

But unlike other icy moons known to possess subglacial oceans, Mimas has a surface with no cracks or melts that could suggest an internal glaciation. It also increases scientists’ confidence that the interior of a small moon like Mimas could be warm enough for the ocean to not freeze.

A planetary scientist who once thought the idea of ​​the Mimas ocean was impossible has now discovered thermodynamics to be plausible.

“I changed my mind recently,” said Alyssa Rhoden, a geophysicist of icy moons at the Southwest Research Institute in Boulder, Colo. is, letting Mimas have an ocean would really challenge our intuition about Mimas. And when I realized that, I thought, that’s not how scientists are supposed to work. We don’t draw conclusions without actually testing the hypothesis.”

Dr. Rhoden, along with Matthew Walker of the Planetary Science Institute, based in Tucson, Ariz., devised a computer simulation to explore the tidal forces of Saturn and Mimas. They found that the heat generated by the tides, which would press on the moon, could be enough to sustain the hypothesized ocean.

“It works beautifully,” Dr. Rhoden said this week.

One of the keys to explaining the lack of cracks is that the ocean, if it exists, formed relatively recently. It can also have a stable or larger size. When water freezes into ice, it expands in volume, and the increased pressure breaks the ice above.

Dr. Rhoden said: “Today’s ice crust cannot thicken. “So the Mimas has to warm up or it has to be stable.”

The hint of a Mimas ocean comes from measurements taken by NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017. Mimas’ orbit is tightly locked to Saturn: The back side of the moon always facing the ringed planet, just as we on Earth see only one Earth’s moon. But in 2014, scientists reported a larger-than-expected wobble in Mimas’ rotation. That suggests either the core of Mimas was stretched out in the direction of Saturn or there was an ocean.

Radwan Tajeddine, lead author of 2014 paper, published in the journal Science. “The amazing thing about this paper is that it actually shows that if you just use reasonable ice properties and apply a more complex model, you can actually have an ocean inside and survive. in.”

William McKinnon, professor of earth and planetary sciences at Washington University in St. Louis, still skeptical. “My short answer is this is unbelievable,” he said in an email. “There isn’t anything about the surface of Mimas that says ‘ocean’ or ‘high thermal current’, unlike Enceladus.”

The other possibility – an elongated solid inside – also remains plausible. The answers may have to wait for a future robotic probe to Saturn that can take more detailed measurements of Mimas.

“It’s another piece in the puzzle,” says Dr. Tajeddine. “This article says the ocean is not a crazy idea.”

https://www.nytimes.com/2022/01/21/science/mimas-ocean-death-star.html Oceans May Lurk Inside Saturn’s ‘Death Star’ Moon

Fry Electronics Team

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