[meteorite-list] Cassini Finds 'Missing Link' Moonlet Evidence in Saturn's Rings

[Ron Baalke]

March 29, 2006

Erica Hupp/Gray Hautaluoma 
Headquarters, Washington 
(202) 358-1237/0668

Carolina Martinez 
Jet Propulsion Laboratory, Pasadena, Calif.
(818) 354-9382 

RELEASE: 06-130

CASSINI FINDS "MISSING LINK" MOONLET EVIDENCE IN SATURN'S RINGS

Scientists with NASA's Cassini mission have found evidence that a new 
class of small moonlets resides within Saturn's rings. There may be 
as many as 10 million of these objects within one of Saturn's rings 
alone. 

The moonlets' existence could help answer the question of 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. 

Careful analysis of high-resolution images taken by Cassini's cameras 
revealed four faint, propeller-shaped double-streaks. These features 
were found in an otherwise bland part of the mid-A ring, a bright 
section in Saturn's main rings. 

Cassini imaging scientists reporting in this week's edition of the 
journal Nature believe the "propellers" provide the first direct 
observation of how moonlets of this size affect nearby particles. 
Cassini took the images as it slipped into Saturn's orbit on July 1, 
2004. 

"These moonlets are likely to be chunks of the ancient body whose 
break-up produced Saturn's glorious rings," said Joseph Burns of 
Cornell University, Ithaca, N.Y. Burns is a co-author of the report. 

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 one-half inch 
across to the size of a small house. Scientists knew about two larger 
embedded ring moons such as 19-mile-wide Pan and 4-mile-wide Daphnis. 
The latest findings mark the first evidence of objects of 
approximately 300 feet in diameter. 

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

"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, an imaging team research associate at Cornell and 
lead author of the Nature paper. 

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 
give scientists confidence in their latest findings. 

"We acquired this spectacular, one-of-a-kind set of images immediately 
after getting into orbit for the express purpose of seeing fine 
details in the rings that we had not seen previously," said Carolyn 
Porco, Cassini imaging team leader and co-author. "This will open up 
a new dimension in our exploration of Saturn's rings and moons, their 
origin and evolution." 

The detection of moonlets embedded in a ring of smaller particles may 
provide an opportunity to observe the processes by which planets form 
in disks of material around young stars, including our own early 
solar system. 

"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," said 
co-author Carl Murray, an imaging team member at Queen Mary, 
University of London. "Cassini is giving us a unique insight into the 
origin of planets." 

The Cassini-Huygens mission is a cooperative project of NASA and the 
European and Italian Space Agencies. The Jet Propulsion Laboratory in 
Pasadena, Calif., manages the mission for NASA's Science Mission 
Directorate. 

For images showing the propeller-shaped features on the Web, visit: 

http://www.nasa.gov/cassini 

For information about NASA and agency programs on the Web, visit: 

http://www.nasa.gov/home 

	
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