[meteorite-list] Saturn Propellers Reflect Solar System Origins

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 8 Jul 2010 11:54:04 -0700 (PDT)
Message-ID: <201007081854.o68Is41q027405_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-227

Saturn Propellers Reflect Solar System Origins
Jet Propulsion Laboratory
July 08, 2010

PASADENA, Calif. - Scientists using NASA's Cassini spacecraft at Saturn
have stalked a new class of moons in the rings of Saturn that create
distinctive propeller-shaped gaps in ring material. It marks the first
time scientists have been able to track the orbits of individual objects
in a debris disk. The research gives scientists an opportunity to
time-travel back into the history of our solar system to reveal clues
about disks around other stars in our universe that are too far away to
observe directly.

"Observing the motions of these disk-embedded objects provides a rare
opportunity to gauge how the planets grew from, and interacted with, the
disk of material surrounding the early sun," said Carolyn Porco, Cassini
imaging team lead based at the Space Science Institute in Boulder,
Colo., and a co-author on the paper. "It allows us a glimpse into how
the solar system ended up looking the way it does."

The results are published in a new study in the July 8, 2010, issue of
the journal Astrophysical Journal Letters.

Cassini scientists first discovered double-armed propeller features in
2006 in an area now known as the "propeller belts" in the middle of
Saturn's outermost dense ring, known as the A ring. The spaces were
created by a new class of moonlets - smaller than known moons, but
larger than the particles in the rings - that could clear the space
immediately around them. Those moonlets, which were estimated to number
in the millions, were not large enough to clear out their entire path
around Saturn, as do the moons Pan and Daphnis.

The new paper, led by Matthew Tiscareno, a Cassini imaging team
associate based at Cornell University, Ithaca, N.Y., reports on a new
cohort of larger and rarer moons in another part of the A ring farther
out from Saturn. With propellers as much as hundreds of times as large
as those previously described, these new objects have been tracked for
as long as four years.

The propeller features are up to several thousand kilometers (miles)
long and several kilometers (miles) wide. The moons embedded in the ring
appear to kick up ring material as high as 0.5 kilometers (1,600 feet)
above and below the ring plane, which is well beyond the typical ring
thickness of about 10 meters (30 feet). Cassini is too far away to see
the moons amid the swirling ring material around them, but scientists
estimate that they are about a kilometer (half a mile) in diameter
because of the size of the propellers.

Tiscareno and colleagues estimate that there are dozens of these giant
propellers, and 11 of them were imaged multiple times between 2005 to
2009. One of them, nicknamed Bleriot after the famous aviator Louis
Bleriot, has been a veritable Forrest Gump, showing up in more than 100
separate Cassini images and one ultraviolet imaging spectrograph
observation over this time.

"Scientists have never tracked disk-embedded objects anywhere in the
universe before now," Tiscareno said. "All the moons and planets we knew
about before orbit in empty space. In the propeller belts, we saw a
swarm in one image and then had no idea later on if we were seeing the
same individual objects. With this new discovery, we can now track
disk-embedded moons individually over many years."

Over the four years, the giant propellers have shifted their orbits, but
scientists are not yet sure what is causing the disturbances in their
travels around Saturn. Their path may be upset by bumping into other
smaller ring particles, or responding to their gravity, but the
gravitational attraction of large moons outside the rings may also be a
factor. Scientists will continue monitoring the moons to see if the disk
itself is driving the changes, similar to the interactions that occur in
young solar systems. If it is, Tiscareno said, this would be the first
time such a measurement has been made directly.

"Propellers give us unexpected insight into the larger objects in the
rings," said Linda Spilker, Cassini project scientist based at NASA's
Jet Propulsion Laboratory in Pasadena, Calif. "Over the next seven
years, Cassini will have the opportunity to watch the evolution of these
objects and to figure out why their orbits are changing."

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission
Directorate in Washington. The Cassini orbiter and its two onboard
cameras were designed, developed and assembled at JPL. The imaging
operations center is based at the Space Science Institute in Boulder, Colo.

For newly released images and more information about the Cassini-Huygens
mission visit: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov
or http://ciclops.org.

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook at jpl.nasa.gov

Joe Mason 720-974-5859
Space Science Institute, Boulder, Colo.
jmason at ciclops.org

2010-227
Received on Thu 08 Jul 2010 02:54:04 PM PDT