The newly plotted moons of Jupiter include one “oddball” that orbits in the wrong direction and may be the remnant of a head-on collision.

Jupiter’s tally of moons just got a little bit larger. A team of astronomers announced today the discovery of 10 additional moons orbiting the largest planet in our solar system, raising Jupiter’s moon total to 79.

The same survey that discovered these 10 also resurveyed two other moons previously discovered by the researchers, who verified the moons’ orbital paths. Of the 12 newly surveyed moons, 11 have orbits that fall neatly in line with previously discovered satellites. Two of those are part of Jupiter’s group of inner prograde moons, meaning that they orbit in the same direction as the planet rotates. Nine others orbit with Jupiter’s outer retrograde moons in the opposite direction.

The twelfth moon, however, is rather peculiar.

“Our other discovery is a real oddball and has an orbit like no other known Jovian moon,” said Scott Sheppard, lead scientist on the project and a staff scientist at the Department of Terrestrial Magnetism in Washington, D. C.

This twelfth moon has a wide, 1.5-Earth-year orbit around Jupiter and travels among the retrograde moons. What makes it odd, however, is its maverick orbit: it is the only prograde Jovian satellite discovered to date to orbit at the same distances as the retrograde moons. The moon, tentatively named Valetudo, also has a more inclined orbit than other prograde moons and is one of the smallest moons of Jupiter discovered to date, measuring less than 1 kilometer in diameter.

The team first observed the new moons in 2017 with the 4-meter Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. They then used telescopes in Chile, Arizona, and Hawaii to confirm the existence of the moons and their orbits around Jupiter, a process that required many follow-up observations over the past year.

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