The big Mimas’ mountain seen by the Cassini space probe

Mimas (Photo NASA/JPL-Caltech/Space Science Institute)
Mimas (Photo NASA/JPL-Caltech/Space Science Institute)

NASA has published a new photo taken by the Cassini space probe of Mimas, one of Saturn’s moons, which provides an excellent perspective view of the mountain in the center of Herschel crater, which is not huge in absolute terms but has a diameter which is almost a third of that of Mimas. The mountain is high even by Earth standards with at least 6 kilometers (4 miles) above the crater’s floor and stands out even more on the small moon.

Mimas was discovered in 1789 by astronomer William Herschel and with its 396 kilometers (246 miles) of average diameter is the smallest known celestial body that has a more or less spherical shape caused by its gravity. In fact, it’s a spheroid because Mimas is noticeably deformed by the Saturn force of gravity. The consequence is that its longest axis is about 10% longer than its shortest one.

Herschel crater, named after astronomer William Herschel, was discovered in 1980 and according to a research is about 4.1 billion years old. If that’s the case it means that it’s the consequence of one of the impacts that were common in the first phase of the solar system’s history, when inside it there were many giant asteroids and planetoids that collided. Fractures visible on the opposite side of Mimas could be traces of the shock waves that followed that impact and almost destroyed this moon.

The dynamics of that kind of impact often lead to the formation of a peak at their centers and that also happened in Herschel crater with the big mountain at its center, which however has estimated depth of at least 10 kilometers (6 miles). The consequence is that the peak doesn’t reach the height of the crater’s edges and for that reason it’s visible in photos taken by the Cassini space probe only when it’s in a favorable position with respect to the mountain.

This photo was taken on October 22, 2016 using a combination of filters that favors wavelengths at ultraviolets around 338 nanometers. The Cassini space probe was at a distance of about 185,000 kilometers (115,000 miles) from Mimas and from that position it was able to get an excellent picture of the mountain at the center of Herschel crater.

The ratio of the diameter of Mimas and that of 139 km (86 miles) of Herschel crater are curiously similar to that of Star Wars’ Death Star and its planet-destroying superlaser weapon. The first move of the saga was released three years before the discovery of the crater so the similarity is a coincidence but NASA mentioned it in some official communications.

From this point of view, Mimas is similar to Tethys, another moon of Saturn with a giant impact crater called Odysseus that made it similar to the Death Star. For this reason, these two moons have become quite famous among the public. In the case of Mimas, the crater is definitely smaller as the Tethys one is larger than the whole Mimas but inside it there’s this big mountain and this new view from an ideal angle will allow to study it better.

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