The most unusual satellites in the solar system that are constantly changing places

Of the variety of satellites available on the planets of the solar system, Janus and Epimetheus stand out for their unusual behavior in orbit. Orbiting Saturn, this couple once in 4 years makes "orbital castling": Janus is in the orbit of Epimetheus, and he, in turn, takes the place of a neighbor. The proximity of their orbits and the unusual game of catching up led to the fact that astronomers did not immediately realize that they were observing two different celestial bodies, and only more detailed studies revealed the existence of two unusual satellites of the gas giant.

Janus and Epimetheus do not differ in large sizes, and therefore are less known to the general public than, for example, Titan or Ray. Janus has an average diameter of 178 kilometers and is presumably composed of ice, having high porosity and low density. His partner with a diameter of 119 kilometers, most likely, is identical to him in composition and structure, while the distance between their orbits is only 50 kilometers. Both satellites revolve around Saturn at a distance of about 90,000 kilometers at an incredible speed: they complete a complete revolution around the planet in just 16.7 Earth hours. But this is not the most surprising in the behavior of these celestial bodies.

It turned out that Janus and Epimetheus periodically change places, and during the observation of them they have done this already several times, each time avoiding collisions and safely occupying a place in orbit, which until recently belonged to a partner. When a satellite in lower orbit approaches a neighbor, they exert a gravitational effect on each other and at some point begin to rotate around a common center of mass. This short rotation ends with the lower satellite moving into the upper orbit, and the upper one taking its place, and this situation repeats every 4 years.