Cassini Catches Meteors Hitting Saturn's Rings
April 29, 2013: NASA's Cassini spacecraft has provided the first direct evidence of small meteoroids crashing into Saturn's rings and breaking into streams of rubble.
These observations make Saturn's rings the only location besides Earth, the moon and Jupiter where astronomers have been able to observe impacts as they occur. The meteoroids Cassini detected range in size from about one-half inch to several yards (1 centimeter to several meters). Scientists scrutinizing images from the probe took 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.
The solar system is full of small, speeding objects such as comet dust and chips off asteroids. These objects frequently pummel planetary bodies.
"The 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," said Matt Tiscareno, lead author of the paper and a Cassini participating scientist at Cornell University in Ithaca, N.Y. "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 meteoroids creates clouds of debris. The tiny particles forming these clouds have a range of orbital speeds around Saturn. As a result they are soon are pulled into diagonal, extended bright streaks such as Cassini observed.
The finding could shed light on a long standing question: How old are Saturn's rings?
"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.
Some estimates have even put the formation of Saturn's rings during the age of dinosaurs on Earth. That would make the rings very young compared to Saturn.
"To assess this dramatic claim, we must know more about the rate at which outside material is bombarding the rings," continues Cuzzi. "This latest analysis helps fill in that story with detection of impactors of a size that we weren't previously able to detect directly."
Cassini -- mission home page
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, 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 team consists of scientists from the United States, the United Kingdom, France and Germany. The imaging operations center is based at the Space Science Institute in Boulder, Colo.