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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Oct 11 18:32:30 2006
Message-ID: <200610112232.PAA02762_at_zagami.jpl.nasa.gov>

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.

-end-
Received on Wed 11 Oct 2006 06:32:28 PM PDT