Saturn Propellers Reflect Solar System Origins

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

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

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

NEWS RELEASE: 2010-227 July 8, 2010

SATURN PROPELLERS REFLECT SOLAR SYSTEM ORIGINS

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-227&cid=release_2010-227

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.

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