Read more: Click here to read the original, longer version of this story. THERE’S more to Mimas than meets the eye. The wobbles of one of Saturn’s smallest moons hint at something unusual beneath the surface – perhaps an ocean. Mimas isn’t the first of Saturn’s moons to show signs of being soggy, but no one expected to find fluids there. “People thought that this was a boring moon,” says Radwan Tajeddine at Cornell University in Ithaca, New York. That picture changed when Tajeddine and his team took a closer look at images from NASA’s Cassini spacecraft. By comparing the position of Mimas’s craters from one image to the next, they found that its rotation was slightly irregular: it was wobbling about twice as much as expected (Science, doi.org/wdw). An ocean some 30 kilometres below the entire surface could explain the swaying. To see why, think of spinning a raw egg and a hard-boiled egg on a table, says Tajeddine. The raw egg will spin more slowly and unevenly as its liquid insides slosh around. Or perhaps Mimas rotates the way it does because its core is shaped more like a rugby ball than a sphere. If Mimas formed out of rocks in Saturn’s rings clumping together, rather than condensing from the same material as the planet, then it could have an odd-shaped core preserved within. An ocean would be an exciting find, but a bumpy interior is more likely, says Francis Nimmo at the University of California, Santa Cruz. “It’s really hard to understand how an ocean could survive for billions of years inside something as small as Mimas.” This article appeared in print under the headline “Saturn’s moon Mimas might host subterranean ocean”More on these topics: