20 new moons discovered around Saturn, now the solar system's 'moon king'

With 80 known moons, the ringed planet has more natural satellites than any other planet.
An artist's conception of the 20 newly discovered moons orbiting Saturn.
An artist's conception of the 20 newly discovered moons orbiting Saturn.NASA/JPL-Caltech/Space Science Institute; Paolo Sartorio/Shutterstock
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By David Freeman

With help from a big telescope and a little detective work, astronomers have discovered 20 new moons in orbit around Saturn.

The discoveries, announced Monday by the International Astronomical Union, bring to 82 the total number of natural satellites known to be circling the sixth planet from the sun.

A gas giant that's the second-largest planet in our solar system, Saturn now has more known moons than any other planet. Jupiter, the largest planet and the previous record holder, has 79 known moons.

“It was fun to find that Saturn is the true moon king for our solar system,” Scott Sheppard, a faculty member at the Carnegie Institution for Science in Washington, D.C., and the leader of the team of astronomers who discovered the moons, told NBC News MACH in an email. He called the moons “remnants of the objects that helped form the planets."

Sheppard is credited with last year's discovery of 12 previously unknown moons around Jupiter, a haul that brought that planet to its 79-moon total. The institution held a contest to name five of those Jovian moons and is holding a similar contest to name all 20 of Saturn's newfound moons. Entries must be submitted via Twitter by Dec. 6.

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The discovery images for one of the the newly found prograde moons of Saturn.Scott Sheppard / via Carnegie Science

Saturn's newfound moons are believed to have arisen after the formation of the planets billions of years ago was mostly complete. Each has a diameter of about 5 kilometers, or 3 miles. Seventeen are in so-called retrograde orbits, meaning their movement is opposite to Saturn’s rotation around its axis. Three are in prograde orbits, meaning they move in the same direction as the planet’s rotation.

The research caused a buzz in the astronomy world.

“I’m super-excited that it’s come out,” said Jackie Faherty, an astrophysicist at the American Museum of Natural History in New York City. The discoveries add to the “forensic evidence” relating to the formation of Saturn and the solar system overall, she added.

“We’ve been to Saturn. Cassini was there, Voyager was there, and we still missed these moons,” Faherty said, referring to NASA space probes that visited Saturn. “It’s a reminder that in astronomy, you can fly right by and right around and still miss things.”

Sheppard’s team discovered the moons by taking a fresh look at observations made more than a decade ago using the Subaru Telescope, an 8.2-meter telescope located atop Mauna Kea, a dormant volcano on the Big Island of Hawaii. “I went back through the old data searching by eye for very faint things our automatic program may have missed,” Sheppard said in the email, adding that it was “a very time-intensive process.”

More Saturnian moons may yet be found. Sheppard said about 100 moons with a diameter of at least one mile are believed to be orbiting the planet — but it will take bigger telescopes to find these tiny bodies, whose small size and extreme distance makes them very hard to observe.

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