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Carnegie Institution for Science/Roberto Molar Candanosa

Ten new moons—including one ‘oddball’—discovered around Jupiter

Jupiter’s orbital family has just rapidly expanded, with scientists today announcing the discovery of 10 new miniature moons around the gas giant. That brings its total known satellites to 79, the most in the solar system.

The new moons, pictured as circles above, were discovered last year by a team of astronomers. After verification, they are being reported today by the International Astronomical Union, based in Paris. At the time, the researchers were searching for a theorized massive planet far beyond Pluto, known as Planet X or Planet Nine, which is thought to be tugging on the orbits of distant solar system objects. Although the scientists’ planet hunt has so far come up dry, the team, using the recently upgraded Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile, also had Jupiter in view, leading to the discovery. Additional observations over a year confirmed the orbits of the moons, all of which are 3 kilometers or less in diameter.

The moonlets mostly follow Jupiter’s known patterns: Located far beyond the planet’s large primary moons (purple), two of the new moonlets belong to a grouping (blue) that spins in the same direction as the planet, all of which are believed to be the fragments of one large shattered moon. Seven fall in a farther out “retrograde” cluster (red) rotating against the planet’s spin, their opposing path kick-started when ancient moons collided with comets, asteroids, or other moons.

But one moon, tentatively dubbed “Valetudo” (green), is an oddball, orbiting with Jupiter’s spin but within the retrograde cluster. The satellite, named for Jupiter’s great-granddaughter, could be a bit of unfinished business, the last remnant of the ancient moons that provided the grist for the retrograde cluster, the team theorizes. Its path weaving within the retrograde moons is unstable, they add; a collision, at some point, is likely. 

*Correction, 17 July, 10:30 a.m: An earlier version of this article misstated the number of new moons discovered. Although the team did discover 12 new moons, two were announced last year.