Wednesday, August 4, 2021

Chariklo, the little lord of the rings

We all know Saturn because of the impressive ring system located around it. However, Saturn is not the only object in the Solar System to present this characteristic: all the other gas giants are in fact surrounded by rings.

But that's not all: surprisingly in orbit between Saturn and Uranus there is an asteroid which is also surrounded by a system of rings! This asteroid, which is called Chariklo, has an average diameter of only 250 km.

The rings were discovered in 2013 during a stellar occultation. Passing in front of a star Chariklo was expected to obscure its light only once, but observations unexpectedly showed several dips in the star's brightness. By studying the data obtained, it was discovered that around the asteroid there were two rings, the first located at a distance of 390 km and 7 km wide and the second 3 km wide and on an orbit with a 405 km semimajor axis.

To date, the mechanisms that keep Chariklo's rings stable are not known. Systems like these orbiting small bodies should in fact disintegrate within a few million years. It has been assumed that the rings are held together by the gravitational action of some shepherd moons, but they have not yet been discovered. Alternatively, it has been supposed that the elongated shape and the fast rotation of the asteroid may contribute to the stability of the rings.

Credit: ESO, L. Calcada.

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