Astronomers find 12 more Jupiter moons, including an 'oddball'

The existence of the moons pushes Jupiter's total satellites to 79.

Eric Mack Contributing Editor
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Eric Mack
2 min read

Jupiter as seen from Hubble.

Space Telescope Science Institute

Jupiter's neighborhood was always crowded, but the discovery of 12 new moons around the giant planet makes it more intriguing.

A team of astronomers has been working since spring of 2017 to confirm the dozen new outer moons, bringing Jupiter's total number of satellites to 79.

"It takes several observations to confirm an object actually orbits around Jupiter," Gareth Williams at the International Astronomical Union's Minor Planet Center, said in a statement. "So, the whole process took a year."  

The discovery helps give astronomers a more complete picture of how the solar system formed and hints at a tumultuous time filled with massive collisions around the giant plant. One of the new moons even suggests we may still be in such a period.

The announcement of the new moons came out Tuesday in the International Astronomical Union Minor Planet Electronic Circular

Watch this: Twelve new Jupiter moons found, including one reckless one

All of the moons orbit much further out than the Galilean moons you may have heard of: Europa, Ganymede, Io and Callisto. Nine of the new satellites orbit in a distant swarm of outer moons that are thought to be leftover from a series of collisions that might have involved what were once three larger bodies. 

Enlarge Image

A look at Jupiter's new moons.

Carnegie Institution for Science

Two of the newly discovered satellites orbit with a group that are in between the outer group and the Galilean moons. This cosmic clique is thought to be fragments of a single larger moon that broke apart.   

Most of the moons are the size of large asteroids, measuring between one and three kilometers (about two-thirds of a mile to two miles) in diameter.

One of the new moons in the outer group is particularly unique, according to astronomer Scott Sheppard at the Carnegie Institution for Science, who led the team that first spotted the moons last year. 

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"Our other discovery is a real oddball and has an orbit like no other known Jovian moon," Sheppard said. "It's also likely Jupiter's smallest known moon, being less than one kilometer in diameter." 

The moon, which has the proposed name Valetudo, orbits in the same direction as Jupiter's rotation, unlike all the other moons in the outer group.

"This is an unstable situation," Sheppard said. "Head-on collisions would quickly break apart and grind the objects down to dust."  

Fortunately, the volatile traffic situation with those outer moons is far removed from the more stable orbit of Europa, which is quickly becoming a primary target in the search for life beyond Earth

First published July 17, 7 a.m. PT. 
Update 11:20 a.m. PT: Adds video. 

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