Saturn Is Making (And Destroying) Mini-Moons All The Time

Saturn’s F ring is a little moon factory

Cassini Imaging Team, SSI, JPL, ESA, NASA

Back in April we introduced you to Peggy, a small moon that was either being born, or torn to bits, in orbit around Saturn. Peggy showed up in the images captured by NASA's Cassini orbiter as a small bright spot, little more than a distortion in Saturn's prominent A ring.

Peggy seemed like a rarity. But now it looks like Peggy—far from a lonely wanderer struggling to hold itself together in chaos—has siblings. Lots of them. Not just the dozens of moons known to orbit the ringed planet, but swarms of mini-moons that are constantly being born and dying in Saturn's rings. According to Deborah Netburn writing for the Los Angeles Times, there's a Saturnian moon born every minute. Or close enough, anyway.

“While most processes in the universe happen on the order of millions and billions of years, the small moons of Saturn's F ring coalesce and disperse in the matter of weeks to months,” says Netburn.

Birthed in the wispy outer F ring, a region of the Saturnian ring system that is barely visible on the outskirts of the more prominent inner rings, these mini-moons grow as small particles of dust and ice glom together “to form small moonlets about the size of a mountain,” says Netburn. “Because they are essentially giant snowballs, they are not inherently stable and can easily be torn apart when something like the 50-mile-wide, potato-shaped moon Prometheus comes nearby.”

Saturn's tale is a lot like that of Jupiter, the gas giant that is constantly capturing, shedding and swallowing potential moons. Or even the Earth, with its ever-shifting roster of moons. It's a reminder that in a place as chaotic as the universe, nothing ever stays the same.

QI's history of "How many moons does the Earth have?"

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