The fact that a planet – like the Earth – has only one single companion, is rather unusual in our Solar System. With 79 moons, the giant planet Jupiter previously had the most moons. Now, it’s been surpassed by Saturn, which changed from having 62 to 82 moons in one fell swoop. The new moons around the ringed planet were discovered using the Subaru telescope on Mauna Kea in Hawaii.
Each of the newcomers has a diameter of about 5 km (3 miles). Seventeen of the twenty are orbiting Saturn in the wrong direction, in what is called a retrograde orbit, that is, in the direction opposite the rotation of the planet. The other three complete their circuit around Saturn the proper way, that is, they have prograde orbits. The fact that the moons were only just discovered is due not only to their small sizes, but also to their wide orbits. Only two of the prograde moons are relatively close to Saturn and need about two years to complete one orbit (the Earth’s moon takes one month). The other 18, in contrast, need more than three Earth years to complete their orbits.