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Carnegie discovery of 20 new moons puts Saturn ahead of Jupiter, with 82


The planet Saturn, as seen from the Cassini spacecraft on July 23, 2008.

Photo: NASA / JPL / Space Science Institute via AP

The solar system has a new winner in the moon department.

Twenty new moons have been found around Saturn, giving the ringed planet a total of 82, scientists said on Monday. That beats Jupiter and its 79 moons.

“It was fun to find that Saturn is the true moon king,” Carnegie Institution for Science astronomer Scott Sheppard said.

If it is any consolation to the Jupiter crowd, our solar system’s biggest planet — Jupiter — still has the biggest moon. Jupiter’s Ganymede is almost half the size of Earth. By contrast, Saturn’s 20 new moons are minuscule, each barely 5km in diameter.

Sheppard and his team used a telescope in Hawaii to spot Saturn’s 20 new moons over the summer. About 100 even tinier moons could be orbiting Saturn, still waiting to be found, he said.


Astronomers have pretty much completed the inventory of moons as small as 5km around Saturn and 1.6km around Jupiter, Sheppard said.

Future larger telescopes would be needed to see anything smaller.

It is harder spotting mini moons around Saturn than Jupiter, given how much farther away Saturn is, Sheppard said.

“So seeing that Saturn has more moons even though it is harder to find them, shows just how many moons Saturn has collected over time,” he wrote in an e-mail.

These baby moons might have come from larger parent moons that broke apart right after Saturn formed.

Seventeen of Saturn’s new moons orbit the planet in the opposite, or retrograde, direction.

The other three circle in the same direction that Saturn rotates. They are so far from Saturn that it takes two to three years to complete a single orbit.

“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,” Sheppard wrote.

Just last year, Sheppard found 12 new moons around Jupiter. The Carnegie Institution had a moon-naming contest for them; another is planned now for Saturn’s new moons .

The jury is still out on whether any planets beyond our solar system have even more moons. For now, Saturn has the most known moons.

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