Astronomers Discover 12 New Moons Around Jupiter, One Of Which Is An 'Oddball'

Jupiter has dozens and dozens of moons in its orbit, but another 12 has just been discovered — including an "oddball" with a precarious orbit.

The gas giant now has a total of 79 known moons, by far the most of any planet in the solar system.

The Regular Moons

Carnegie Institution for Science reports that out of the 12 newly discovered moons, 11 appear totally normal.

Nine moons are part of the planet's outer swarm of moons, orbiting in retrograde or in the opposite direction of Jupiter's spin rotation. These take two years to orbit the planet. Two are part of the inner moons, orbiting in the prograde or with the planet's rotational direction. This pair of moons take less than a year to orbit Jupiter.

The Odd One Out

Of course, the star of the discovery, presented during the International Astronomical Union on Tuesday, July 17, is the so-called oddball planet. This runt is Jupiter's smallest known moon with a diameter of only 1 kilometer or a little over half a mile.

It orbits in the prograde and takes about a year and a half to circle Jupiter, but it doesn't behave quite like the rest of the group. The oddball is farther and more inclined than the other prograde moons, and its journey takes it through the orbits of the retrograde moons. This strange orbit makes it prone to collisions with the retrograde moons that are moving in the opposite direction.

"This is an unstable situation," Scott Sheppard of Carnegie says in a statement. "Head-on collisions would quickly break apart and grind the objects down to dust."

In fact, scientists suggest that this tiny moon could be the final remnant of a bigger oddball prograde moon that has been ground down to a smaller size after previous collisions. This hypothetical large prograde moon may also have formed some retrograde moon groupings.

The oddball moon is named Valetudo, after the great-granddaughter of the Roman god Jupiter.

An Accidental Discovery

Led by Sheppard, a team of scientists were looking at the outer fringes of the solar system for distant objects, and the gigantic planet was simply in their line of sight.

"Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant Solar System objects, so we were serendipitously able to look for new moons around Jupiter while at the same time looking for planets at the fringes of our Solar System," Sheppard says.

According to Wired, astronomers have already searched this region of Jupiter before, but their instrument DECam was able to detect smaller, darker objects that are easy to miss using older equipment.