by Denise Chow
SPACE Staff Writer
July 08, 2010
Giant propeller-shaped structures have
been discovered in the rings of Saturn and appear to be created by a
new class of hidden moons, NASA announced Thursday.
NASA's Cassini spacecraft spotted the distinctive structures inside
Saturn's rings, marking the first time scientists have
managed to track the orbits of individual objects from within a
debris disk like the one that makes up Saturn's complicated ring
"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 the
study's co-author Carolyn Porco, one of the lead researchers on the
Cassini imaging team based at the Space Science Institute in
"It allows us a glimpse into how the solar system
ended up looking the way it does."
Photos of the propellers taken by Cassini show them to be
structures several thousands of miles long.
propeller-shaped structure created by an unseen moon
illuminated on the sunlit side of Saturn's rings
in this image
obtained by NASA’s Cassini spacecraft.
The image was
released on July 8, 2010.
By understanding how
they form, astronomers hope to glean insight into the debris disks
around other stars as well, researchers said.
The results of the study are detailed in the July 8 issue of the
journal Astrophysical Journal Letters.
Propellers at Saturn
Cassini scientists have seen double-armed propeller structures in
Saturn's rings before, but on a smaller scale than the larger,
They were first spotted in 2006 in an area now
known as the "propeller belt," which is located in the middle of
Saturn's outermost dense ring - the A ring.
The propellers are actually gaps in the ring material were created
by a new class of objects, called moonlets, that are smaller than
known moons but larger than the particles making up Saturn's rings.
It is estimated that these moonlets could number in the millions,
according to Cassini scientists.
The moonlets clear the space immediately around them to generate the
propeller-like features, but are not large enough to sweep clear
their entire orbit around Saturn, as seen with the moons Pan
and Daphnis (photos of Saturn rings and moons below.)
But in the new study, researchers a new legion of larger and rarer
moons in a separate part of the A ring, farther out from Saturn.
These much larger moons create propellers that are hundreds of times
larger than those previously described, and these objects have been
tracked for about four years.
The study was led by Cassini imaging team associate Matthew Tiscareno at Cornell University in Ithaca, N.Y.
The propeller features for these larger moons are up to thousands of
miles long and several miles wide. The moons embedded in Saturn's
rings appear to kick up ring material as high as 1,600 feet (0.5 km)
above and below the ring plane.
This is much greater than the typical ring thickness of about 30
feet (10 meters), researchers said.
Hidden Saturn moons
Cassini spacecraft is too far away to see the moons amid
the swirling ring material that surrounds them. Yet, scientists
estimate that the moons measure approximately half a mile (about one
km) in diameter, based on the size of the propellers.
According to their research, Tiscareno and his colleagues estimate
that there are dozens of these giant propellers. In fact, 11 of them
were imaged multiple times between 2005 and 2009.
One such propeller, nicknamed Bleriot after the famous aviator
Bleriot, has shown up in more than 100 separate Cassini images and
one ultraviolet imaging spectrograph observation during this time.
"Scientists have never tracked disk-embedded objects anywhere in the
universe before now," said Tiscareno.
"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 their four years of observation, the researchers noticed shifts
in the orbits of the giant propellers as they travel around Saturn,
but the cause of these disturbances have not yet been determined.
The shifting orbits could be caused by collisions with other smaller
ring particles, or could be responses to these particles' gravity,
the researchers said. The orbital paths of these moonlets could also
be altered due to the gravitational attraction of large moons
outside of Saturn's rings.
Scientists will continue to monitor the moons to see if the disk
itself is driving the chances, similar to the interactions that
occur in young solar systems.
If so, 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
NASA launched the
Cassini probe in 1997 and it arrived at Saturn in
2004, where it dropped the European
Huygens probe on the cloudy
Titan, Saturn's largest moon.
Saturn gets a new
look in this new image
taken by the Cassini
spacecraft studying the ringed planet.
The vivid orange and
yellow hues of Saturn's atmosphere,
and the blue tinge of
its rings at far right,
composite of several images taken by Cassini's wide-angle camera.
To build this view,
researchers used special camera filters
that are sensitive
only to certain types of infrared light.
recorded this image on Dec. 13, 2006
from a distance of
about 511,000 miles (822,000 kilometers) from Saturn.
Cassini was slated to be
decommissioned in September of this year (2010), but received a life
extension that now runs through 2017.