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Saturn unseats Jupiter as planet with the most moons in our solar system

Astronomers discovered 20 new moons around Saturn, bringing its total to 82.

ByKatherine J. WuNOVA NextNOVA Next
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The latest view of Saturn from NASA's Hubble Space Telescope. Not pictured: 82 moons, 20 of which are newly discovered. Image Credit: NASA, ESA, A. Simon (GSFC), M.H. Wong (University of California, Berkeley) and the OPAL Team

When it comes to amassing moons, there’s no beating Jupiter’s veritable cosmic cavalry of 79. Until now.

According to an announcement made by the International Astronomical Union’s Minor Planet Center on Monday, researchers have discovered an additional 20 moons orbiting Saturn, bringing its grand total to a whopping 82. The numbers are close, but for now, it’s official: In our solar system, the planet with the most extensive ring system also boasts the largest lunar load.

The findings are the newest notches in the belt of astronomer and lunar enthusiast Scott Sheppard of the Carnegie Institution for Science, who also took part in unveiling Jupiter’s 12 newest moons last year. But even for someone who’s helped pinpoint dozens of these distant orbs, Sheppard stresses that his job is tough. Far-off moons are dim and tough to spot, he told George Dvorsky at Gizmodo, especially when they’re less than three miles across—a criterion that all 20 of Saturn’s new additions meet.

The latest discoveries were made possible by Hawaii’s Subaru telescope. After scanning the skies from year to year, the researchers used a computer algorithm to link the data through time and confirm that the moons were indeed reliably orbiting Saturn.

Three of the new moons orbit in the same direction as Saturn’s rotation, while the other 17 move the other way—something that likely reflects how the space rocks were first snared by the planet. All of them circle the planet from relatively far away. One takes about 5.3 years to make the full trip around the gas giant, earning it the title of Saturn’s farthest known moon.

There’s a lot left to learn, but for now the researchers have placed the moons into three broad families based on their orbits. The members of each cluster probably originated from the same source—perhaps a big parent body that fragmented from a collision during Saturn’s early days, Sheppard told Michael Greshko at National Geographic.

Similar groupings appear to be true of Jupiter’s moons as well, Sheppard said in a press release. “We think these moons are basically showing us how chaotic the solar system was in the very distant past,” he told Greshko.

That means learning more about these moons could reveal some crucial intel about the solar system’s youth, and how the planets originally came together.

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With Jupiter and Saturn neck and neck, this cosmic contest isn’t over yet. Sheppard suspects there are still more moons out there around these planets and their more-distant neighbors, Uranus and Neptune, that are too small to be detected by available telescopes, Dvorsky reports.

Those neglected moons may yet have their day in the sun, thanks to some of the ultra-sensitive “next-generation” telescopes in the works, Greshko reports. In the meantime, Sheppard has invited the public to suggest names for the new moons in a contest. Not everything is fair game, though, according to the press release: The moons must be named after giants from Norse, Gallic, or Inuit mythology.

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