Five images of Saturn's rings, taken by
NASA's Cassini spacecraft between 2009 and 2012, show clouds of material
ejected from impacts of small objects into the rings. Image Credit:
NASA/JPL-Caltech/Space Science Institute/Cornell. › Full image and caption
PASADENA, Calif. -- NASA's Cassini spacecraft has provided the first
direct evidence of small meteoroids breaking into streams of rubble and
crashing into Saturn's rings.
These observations make Saturn's rings the only location besides Earth,
the moon and Jupiter where scientists and amateur astronomers have been
able to observe impacts as they occur. Studying the impact rate of
meteoroids from outside the Saturnian system helps scientists understand
how different planet systems in our solar system formed.
The solar system is full of small, speeding objects. These objects
frequently pummel planetary bodies. The meteoroids at Saturn are
estimated to range from about one-half inch to several yards (1
centimeter to several meters) in size. It took scientists years to
distinguish tracks left by nine meteoroids in 2005, 2009 and 2012.
Details of the observations appear in a paper in the Thursday, April 25 edition of Science.
Results from Cassini have already shown Saturn's rings act as very
effective detectors of many kinds of surrounding phenomena, including
the interior structure of the planet and the orbits of its moons. For
example, a subtle but extensive corrugation that ripples 12,000 miles
(19,000 kilometers) across the innermost rings tells of a very large
meteoroid impact in 1983.
"These new results imply the current-day impact rates for small
particles at Saturn are about the same as those at Earth -- two very
different neighborhoods in our solar system -- and this is exciting to
see," said Linda Spilker, Cassini project scientist at NASA's Jet
Propulsion Laboratory in Pasadena, Calif. "It took Saturn's rings acting
like a giant meteoroid detector -- 100 times the surface area of the
Earth -- and Cassini's long-term tour of the Saturn system to address
this question."
The Saturnian equinox in summer 2009 was an especially good time to see
the debris left by meteoroid impacts. The very shallow sun angle on the
rings caused the clouds of debris to look bright against the darkened
rings in pictures from Cassini's imaging science subsystem.
"We knew these little impacts were constantly occurring, but we didn't
know how big or how frequent they might be, and we didn't necessarily
expect them to take the form of spectacular shearing clouds," said Matt
Tiscareno, lead author of the paper and a Cassini participating
scientist at Cornell University in Ithaca, N.Y. "The sunlight shining
edge-on to the rings at the Saturnian equinox acted like an
anti-cloaking device, so these usually invisible features became plain
to see."
Tiscareno and his colleagues now think meteoroids of this size probably
break up on a first encounter with the rings, creating smaller, slower
pieces that then enter into orbit around Saturn. The impact into the
rings of these secondary meteoroid bits kicks up the clouds. The tiny
particles forming these clouds have a range of orbital speeds around
Saturn. The clouds they form soon are pulled into diagonal, extended
bright streaks.
"Saturn's rings are unusually bright and clean, leading some to suggest
that the rings are actually much younger than Saturn," said Jeff Cuzzi, a
co-author of the paper and a Cassini interdisciplinary scientist
specializing in planetary rings and dust at NASA's Ames Research Center
in Moffett Field, Calif. "To assess this dramatic claim, we must know
more about the rate at which outside material is bombarding the rings.
This latest analysis helps fill in that story with detection of
impactors of a size that we weren't previously able to detect directly."
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. NASA's Jet
Propulsion Laboratory, Pasadena, Calif., a division of the California
Institute of Technology, Pasadena, manages the Cassini-Huygens mission
for NASA's Science Mission Directorate in Washington. JPL designed,
developed and assembled the Cassini orbiter and its two onboard cameras.
The imaging team consists of scientists from the United States,
England, France and Germany. The imaging operations center is based at
the Space Science Institute in Boulder, Colo.
For images of the impacts and information about Cassini, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .
Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
Dwayne Brown 202-358-1726
NASA Headquarters, Washington
