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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Mar 30 21:42:39 2006
Message-ID: <200603301804.k2UI4E705962_at_zagami.jpl.nasa.gov>

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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Received on Thu 30 Mar 2006 01:04:13 PM PST