Cassini reveals 10 million tiny satellites around Saturn

As many as 10 million of tiny satellites, some up to 100 meters in diameter, are orbiting Saturn within its rings, scientists with NASA's Cassini mission reported on Wednesday.

The findings were published in the March 30 issue of the journal Nature. Cassini took high-resolution images as it slipped into Saturn orbit on July 1, 2004, the researchers said.

Careful analysis of these pictures revealed four faint, propeller-shaped double streaks in an otherwise bland part of the mid-A Ring, a bright section in Saturn's main rings.

The researchers believe the "propellers" provide the first direct observation of how moonlets of 100 meters in diameter affect nearby particles.

From the number of moonlets spotted in the very small fraction of the A ring seen in the images, the researchers estimated the total number of moonlets to be about 10 million.

Previous measurements, including those made by NASA's Voyager spacecraft in the early 1980s, have shown that Saturn's rings contain mostly small water-ice particles ranging from less than 1 centimeter across to the size of a small house.

Scientists knew about two larger embedded ring moons, 30-kilometer-wide Pan and 7-kilometer-wide Daphnis. The latest findings mark the first evidence of objects of about 100 meters in diameter.

"The discovery of these intermediate-sized bodies tells us that Pan and Daphnis are probably just the largest members of the ring population, rather than interlopers from somewhere else," said Matthew Tiscareno, lead author of the study.

Moons as large as Pan and Daphnis clear large gaps in the ring particles as they orbit Saturn. In contrast, smaller moonlets are not strong enough to clear out the ring, resulting in a partial gap centered on the moonlet and shaped like an airplane propeller.

Such features created by moonlets were predicted by computer models, which gave scientists confidence in their latest findings.

The existence of this new class of small moonlets, the researchers said, could help answer the question: whether Saturn's rings were formed through the break-up of a larger body, or are the remnants of the disk of material from which Saturn and its moons formed?

"This will open up a new dimension in our exploration of Saturn's rings and moons, their origin and evolution," said Carolyn Porco, lead scientist of the Cassini imaging team.

These moonlets are likely to be chunks of the ancient body whose break-up produced Saturn's glorious rings, according to Joseph Burns, a co-author of the Nature paper.

Or, the formation of such moonlets in small particles could resemble the birth of planets in dust disks around young stars, including our own early solar system, other scientists imagined.

"Cassini is giving us a unique insight into the origin of planets," said co-author Carl Murray, also a Cassini imaging scientist.

"The structures we observe with Cassini are strikingly similar to those seen in many numerical models of the early stages of planetary formation, even though the scales are dramatically different," he noted in a statement.

Source: Xinhua