Whoa, Astronomers Just Found 20 News Moons Around Saturn

Image: NASA/JPL-Caltech/Space Science Institute

A survey of Saturn’s outer reaches has resulted in the discovery of no less than 20 new moons. With its 82 natural satellites, Saturn now boasts the most moons of any planet in the solar system, surpassing Jupiter’s 82 moons.

It’s always special when astronomers spot new moons, but this is intense—20 new moons confirmed all at once, as announced earlier today by the International Astronomical Union’s Minor Planet Center.


The team credited with the discovery includes Scott Sheppard from the Carnegie Institution for Science, David Jewitt of UCLA, and Jan Kleyna from the University of Hawaii. The distant orbs were spotted with the Subaru telescope located on Hawaii’s Mauna Kea, according to a Carnegie press release.

As you might recall from last year, Sheppard was involved in the discovery of 12 new moons around Jupiter, bring the Jovian giant’s total to 79. The new discovery now brings Saturn’s total up from 62 to 82—the most in the solar system.

“Finding new moons of the planets is hard because they are generally very faint and thus hard to track year to year in order to get reliable orbits for them,” explained Sheppard in an email to Gizmodo. “I have been using some of the largest telescopes in the world to find the new moons and an updated computer algorithm to link the new discoveries year to year, allowing us to officially determine they are orbiting Saturn and thus are new moons of Saturn.”

Two of the new Saturnian moons, shown between the yellow crosshairs.
Image: Scott Sheppard

When asked why it took so long to find these new moons, Sheppard said it’s because they’re so dim. Currently, astronomers are “only able to find moons that are a a few miles in size around Saturn because the planet is so far away,” he said. Sheppard and his colleagues suspects there are around 100 moons around Saturn larger than one mile in size, “but future larger telescopes will be needed to find these smaller and thus fainter moons.”


Each of Saturn’s newly discovered moons measures between 3 to 4 kilometers (1.9 to 2.5 miles) in diameter, so yeah, they’re tiny. Of the 20 moons, 3 are in prograde orbit (moving in the same direction of Saturn’s rotation) and 17 are in retrograde orbit (you guessed it, moving in the opposite direction of Saturn’s rotation.

All of the new moons are relatively far from Saturn. Two of the prograde moons require around two years to make a complete orbit of the gas giant, while the remaining 18 moons (17 retrograde and 1 prograde) require more than three years to make a single orbit (our Moon requires 27 days to make a complete rotation around Earth). The most extreme of these new moons, designated S5613a2 m, requires 1,413 days to revolve around Saturn, or 3.87 years, making it the farthest known moon from the gas giant.

Artist’s conception of the 20 newly discovered moons orbiting Saturn, showing the three groupings and direction of orbit.
Image: Saturn image is courtesy of NASA/JPL-Caltech/Space Science Institute. Starry background courtesy of Paolo Sartorio/Shutterstock

The new moons were slotted into three distinct categories depending on the angles at which they orbit around Saturn.


Two of the prograde moons were assigned to the Inuit group (shown in blue in the graphic above), the moons of which are named after Inuit mythology. The Inuit moons are likely remnants of a large moon or object that disintegrated into smaller fragments a long time ago. The remaining prograde moon was placed in the Gallic group (shown in green), but it’s much further out than previously known Gallic moons, so this designation may or may not stick. All 17 of the retrograde moons have similar inclinations to the Norse group (shown in red), so that’s where they’ve been placed. The Norse group, like the Inuit group, is believed to have originated from a much larger object that broke up into smaller pieces, likely from a collision.

Saturn is further away from the Earth than Jupiter, so it’s tougher to find moons around Saturn. Seeing that Saturn “has more moons even though it is harder to find them, shows just how many moons Saturn has collected over time,” Sheppard told Gizmodo. “Because these new moons are on inclined orbits far from Saturn itself, we believe these new moons were captured by Saturn just after the planet formation process. These moons are the remnants of the objects that helped form the planets, so by studying them, we are learning about what the planets formed from.”

Excitingly, a contest has been created for the public to choose names for the 20 moons. Sorry, but Saturn McMoonyFace won’t be allowed, as the names have to conform to their mythological groupings, along with other naming conventions.


Welcome new moons! We look forward to learning your new names.

Correction: A previous version of this article stated that one of the new moons has an orbital period of 5.3 years. The correct figure is 3.87 years. We regret the error.


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About the author

George Dvorsky

George is a senior staff reporter at Gizmodo.