[meteorite-list] Saturn's Rings Show Evidence of a Modern-Day Collision

[Ron Baalke]

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

Carolina Martinez  818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
								
Preston Dyches   720-974-5859
Cassini Imaging Central Laboratory for Operations 
Space Science Institute, Boulder, Colo.

Image Advisory: 2006-127    		Oct. 11, 2006

Saturn's Rings Show Evidence of a Modern-Day Collision

Scientists with NASA's Cassini mission have spied a new, 
continuously changing feature that provides circumstantial 
evidence that a comet or asteroid recently collided with 
Saturn's innermost ring, the faint D ring.

Imaging scientists see a structure in the outer part of 
the D ring that looks like a series of bright ringlets 
with a regularly spaced interval of about 30 kilometers 
(19 miles). An observation made by NASA's Hubble Space 
Telescope in 1995 also saw a periodic structure in the 
outer D ring, but its interval was then 60 kilometers 
(37 miles).  Unlike many features in the ring system that 
have not changed over the last few decades, the interval 
of this pattern has been decreasing over time.

These findings are being presented today at the Division 
for Planetary Sciences Meeting of the American Astronomical 
Society held in Pasadena, Calif.  Images are available at 
http://www.nasa.gov/cassini , http://saturn.jpl.nasa.gov and 
http://ciclops.org .

"This structure in the D ring reminds us that Saturn's 
rings are not eternal, but instead are active, dynamical 
systems, which can change and evolve," said Dr. Matt Hedman, 
Cassini imaging team associate at Cornell University, 
Ithaca, N.Y.

When Cassini researchers viewed the D ring along a line of 
sight nearly parallel to the ringplane, they observed a 
pattern of brightness reversals: a part of the ring that 
appears bright on the far side of the rings appeared dark 
on the near side of the rings, and vice versa.

This phenomenon would occur if the region contains a sheet 
of fine material that is vertically corrugated, like a tin 
roof. In this case, variations in brightness would 
correspond to changing slopes in the rippled ring material.

Both the changes over time and the "corrugated" structure 
of this region could be explained by a collision of a comet 
or meteoroid into the D ring, which then kicked out a cloud 
of fine particles.  This cloud might have inherited some of 
the tilt of the colliding object's path as it slammed into 
the rings. An alternate explanation could be that the 
object struck an already inclined moonlet, shattering it to 
bits and leaving its debris in an inclined orbit.

In either case, the researchers speculate the aftermath of 
such a collision would be a ring slightly tilted relative 
to Saturn's equatorial plane. Over a period of time, as 
the inclined orbits of the ring particles evolve, this flat 
sheet of material would become a corrugated spiral that 
appears to wind up like a spring over time, which is what 
was observed. 

Based on observations between 1995 and 2006, scientists 
reconstructed a timeline and estimated that the collision 
occurred in 1984.

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, Washington. The Cassini orbiter and its two 
onboard cameras were designed, developed and assembled at 
JPL. The imaging team is based at the Space Science 
Institute, Boulder, Colo.

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