Saturn’s satellite Mimas./Nature
Analysis has shown that an ocean exists on Mimas, one of Saturn’s 146 moons. Analysis based on orbital observations of Mimas showed that in order for the center to be composed of only solids, it would have to be shaped like a ‘pancake’, but this is not the case.
The research team of Valery Lainey, an astronomical scientist at the Paris Observatory of PSL Research University in France, published research results in the international academic journal Nature on the 8th showing that an ocean may exist inside Saturn’s satellite Mimas.
Mimas is a small moon of Saturn, discovered by British astronomer William Herschel in 1789. Mimas has an average diameter of 396.4 km, which is about the distance from Seoul to Busan, and has the smallest mass among the solar system bodies with an ellipsoid shape. Mimas is characterized by having a ‘Herschel Crater’ with a diameter of 139 km, which is one-third the size of its diameter.
Another characteristic of Mimas is that it has a slightly elongated oval shape. This is because Mimas has the same rotation period as Saturn, making it a synchronous satellite with one side constantly facing the parent planet. Depending on the shape of Mimas, two possibilities have been proposed in the astronomical community. The hypothesis is that there is a solid rocky core inside Mimas and that there is liquid inside like Earth.
Until now, the prevailing theory about Mimas was that its center was made of rock. The only moons in the solar system that have an internal ocean are Jupiter’s Europa and Saturn’s Enceladus. In particular, Mimas was not expected to have an ocean inside the satellite because the conditions for maintaining oceans and the way they indicated the presence of oceans were different. Europa and Enceladus sometimes emit water vapor into space through cracks on their surfaces.
Graphics = Seohee Jeong
The research team analyzed observation data from NASA’s Cassini spacecraft, which explored the vicinity of Saturn, to look into Mimas. In particular, we focused on the satellite’s movements, such as Mimas’ orbit and rotation speed. As a result of the analysis, the elliptical egg-shaped Mimas did not follow the same orbit, but was constantly changing its orbit depending on the counter-rotating force.
The research team believed that a unique inertia that resisted the satellite’s rotational acceleration was at work and simulated the case where the center of Mimas was solid and when it was liquid. According to the research team’s simulation, the results showed that if the interior of Mimas was made only of solids, the shape of the satellite should be flat like a pancake. Rather, it was concluded that if the area between the surface and the center were made of liquid, it would be closer to the current form of Mimas.
The ocean in Mimas appears to have been formed relatively more recently than other oceanic moons. The research team explained that Mimas, unlike other ocean satellites, has a thickness of 20 to 30 km between the surface and the sea, so no water vapor is spewed out. The external impact created a huge Herschel crater, but the lack of a gap for water vapor to escape was also presented as evidence for a ‘young sea’. The research team determined that the sea of Mimas was formed between 25 and 2 million years ago.
“(This study) suggests that Mimas’ recent processes may have been common in the early stages of the formation of other moons with oceans,” Alyssa Rhoden, a senior scientist at the Southwest Research Institute, told Nature. a) The idea of having a relatively young ocean is encouraging, as is the possibility that transformative processes may have occurred on Mimas as well.”
“Intuition is excellent for generating hypotheses, but it is not sufficient for drawing conclusions,” he said, adding, “Researchers must be sufficiently open to new ideas and unexpected possibilities.”
References
Nature, DOI: https://doi.org/10.1038/s41586-023-06975-9
