Mini-moons discovered in never-ending birth and death cycle around Saturn

The ultimate in cosmic recycling appears to be happening in our local solar neighbourhood, within the rings of Saturn, according to a new study in the journal Icarus.

Tiny moons, called moonlets, strewn throughout the complex system of rings that grace the gas giant appear to be continually born and destroyed over the course of just hours and days.

In terms of astronomical events, this is almost unheard of; most kinds of cosmic drama we know about in the universe occur over timescales measured in decades if not eons. This makes the discovery of birth and death occurring so rapidly over such a brief cosmological interval really surprising.

Scientists looked at snapshots of the rings sent back 30 years ago by the Voyager probes that swung by Saturn and compared it to those just beamed back by NASA’s Cassini spacecraft now orbiting the ringed world.

They discovered that in one particular ring - known as the F-ring - there were dramatic changes in its appearance in just the last three decades.

“The F-ring is a narrow, lumpy feature made entirely of water ice that lies just outside the broad, luminous rings A, B, and C,” said the co-author Robert French, an astronomer at the SETI Institute in Mountain View, California, in a news press statement.

“It has bright spots. But it has fundamentally changed its appearance since the time of Voyager. Today, there are fewer of the very bright lumps.”

And when the investigators looked closely at the latest Cassini images being beamed back to Earth from over a billion kilometres away, they noticed mysterious bright spots within the rings that were coming and going over the course of hours and days.

"We believe the most luminous knots occur when tiny moons, no bigger than a large mountain, collide with the densest part of the ring," said French in a recent release.

"These moons are small enough to coalesce and then break apart in short order.”

Researchers believe these collisions occur at a special distance around Saturn called the Roche limit, where moons can be pulled apart due to the strong gravitational tugs caused by the large mass of Saturn.

"These newborn moonlets will repeatedly crash through the F ring, like bumper cars, producing bright clumps as they careen through lanes of material," added SETI’s Mark Showalter. "But this is self-destructive behavior, and the moons - being just at the Roche limit - are barely stable and quickly fragmented."

The genesis of these majestic rings themselves have been a great mystery for generations of astronomers. Made up of countless ice boulders, the rings stretch more than 220,000 kilometers across, barely fitting in between the space separating the Earth and our moon. Current leading theory suggests that a collision between an ancient moon and a wayward asteroid or comet may have blasted that giant moon into smithereens, sending the rubble into orbit around Saturn - which we still see today.

By studying these weird demolition events going around our neighbouring planets, astronomers are getting a better grasp on understanding the secrets behind the recipe for making and forming worlds, even like our own.

“The sort of processes going on around Saturn are very similar to those that took place here 4.6 billion years ago, when the Earth and the other large planets were formed,” explained French. “It’s an important process to understand.”