Saturn's moon Enceladus has a warm ocean that's one of the most promising places to look for extraterrestrial life. Now it seems that ocean may stay warm thanks to a quirk in the moon's core.

Because Enceladus is so small, it doesn't have a solid core like Earth's, but rather a porous one. According to a study published today in Nature Astronomy by a team led by the University of Nantes, that core may be the key.

The Fire Inside

The scientists compiled various observations from the Cassini spacecraft, which studied Saturn and its moons for 13 years before falling into the planet forever this September. When it arrived in the Saturn system in 2004, the Cassini mission saw that Enceladus was shooting geysers out its south pole hundreds of miles into space. Something had to be creating liquid water below, and eventually a consensus built: there is a large liquid ocean on this little moon moon.

This new study say, Enceladus's small size (about 150 miles in diameter) means its core isn't rocky, but sort of mushy. It takes in water from the ocean, and that water comprises up to 20 percent of the core materials. "What we have in mind is not a sponge like porosity, it's more like a pile of sand or gravel," says Gael Choblet of Nantes, coauthor of the paper.

The rest of the core materials may experience radioactive decay and tidal forces to stay hot, which also heats up the water into super-hot jets moving toward the north and south pole. This affects the ice shell and keeps it fairly thin in those regions, which creates a geyser effect at the south pole.

Choblet says there's a preliminary indication of some kind of geologic activity at the moon's north pole, but that it's far less active. Partly, this owes to the thickness at the north pole — it's 7 miles deep, where other areas have a surface layer of ice about 15 to 20 miles above the ocean surface. The south pole, on the other hand, is cracked enough that water seeps through a thin ice layer out into interstellar space. "The motion of the porous floor of the liquid water produces very novel and very hot features at the poles," Choblet says.

Carly Howett, a senior research scientist at the Southwest Research Institute who was not involved with the paper, says this study takes modeling of Enceladus's core to a new level and goes a long way toward explaining the geyser activity.

"The difference between these results and previous models is not that surprising (porous cores would deform more until tidal stresses, and thus are heated more). But the magnitude of the heating is encouraging in explaining the high heat flows we see on the surface," she says. "Some of my work indicated it could be as high as 16 gigawatts across Enceladus' south polar terrain."

Hotspots for Life

Why does this all matter? On Earth, anywhere there's water, there's life. So if we're searching for aliens big or small, watery worlds are a good place to start, and Enceladus has a ton of it. Cassini evidence shows that the moon may have complex chemistry, including chemicals associated with earthly ocean floor features called hydrothermal vents, where life on our own planet may have started.

"In our view, these hotspots at the base of the ocean would create the vents that thin the ice above," Choblet says. And from there? With all the right ingredients, we might have the best place to find alien life in our own solar system and confirm that life isn't just exclusive to Earth.

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