Science Focus - the home of BBC Science Focus Magazine
New moons discovered orbiting Saturn takes total to 82 © Nasa/PA

New moons discovered orbiting Saturn takes total to 82

Published: 08th October, 2019 at 11:00
Subscribe to BBC Science Focus Magazine and get 6 issues for just £9.99

Saturn’s 20 new moons are minuscule, each barely 3 miles in diameter.

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. That beats Jupiter and its 79 moons.

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

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 three miles in diameter.

Mr Sheppard and his team used a telescope in Hawaii to spot Saturn’s 20 new moons over the summer.

About 100 even tinier moons may be orbiting Saturn, still waiting to be found, he said.

Read more about the Solar System:

Astronomers have pretty much completed the inventory of moons as small as three miles around Saturn and one mile around Jupiter, according to Mr Sheppard.

Future larger telescopes will be needed to see anything smaller.

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

“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 email.

These baby moons may 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.

Reader Q&A: Why does Saturn have rings?

Asked by Richard O’Neill, Glasgow

It is not entirely clear why Saturn possesses rings. Astronomers have developed three theories of their formation. They could have formed from material left over from the formation of the planet itself – material that was unable to form a moon. Or, they could have formed from the debris of a moon that was destroyed by a large impact, perhaps by a comet or asteroid. Finally, they may have formed from a moon that broke apart due to the tidal forces from Saturn itself.

If the rings were formed along with the planet, then they will have had about four billion years to gather a large amount of ‘dirt’ from micrometeorite impacts. However, Saturn’s rings (composed mostly of water ice) are almost completely devoid of such ‘dirt’, implying they are actually quite young. This may suggest the impacted moon hypothesis is more likely. However, the jury is still out on this question.

Read more:

“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,” Mr Sheppard wrote.

Just last year, Mr 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.

Monday’s announcement came from the International Astronomical Union’s Minor Planet Centre.


Follow Science Focus on Twitter, Facebook, Instagram and Flipboard


Alexander McNamaraOnline Editor, BBC Science Focus

Alexander is the former Online Editor at BBC Science Focus.


Sponsored content