[meteorite-list] Cassini Reveals New Ring Quirks, Shadows During Saturn Equinox

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 21 Sep 2009 13:00:24 -0700 (PDT)
Message-ID: <200909212000.n8LK0Ow6016052_at_zagami.jpl.nasa.gov>

Sept. 21, 2009

Dwayne C. Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov

Jia-Rui C. Cook
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0850
jia-rui.c.cook at jpl.nasa.gov

RELEASE: 09-217

CASSINI REVEALS NEW RING QUIRKS, SHADOWS DURING SATURN EQUINOX

PASADENA, Calif. -- NASA scientists are marveling over the extent of
ruffles and dust clouds revealed in the rings of Saturn during the
planet's equinox last month. Scientists once thought the rings were
almost completely flat, but new images reveal the heights of some
newly discovered bumps in the rings are as high as the Rocky
Mountains. NASA released the images Monday.

"It's like putting on 3-D glasses and seeing the third dimension for
the first time," said Bob Pappalardo, Cassini project scientist at
NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This is among
the most important events Cassini has shown us."

On Aug. 11, sunlight hit Saturn's rings exactly edge-on, performing a
celestial magic trick that made them all but disappear. The spectacle
occurs twice during each orbit Saturn makes around the sun, which
takes approximately 10,759 Earth days, or about 29.7 Earth years.
Earth experiences a similar equinox phenomenon twice a year; the
autumnal equinox will occur Sept. 22, when the sun will shine
directly over Earth's equator.

For about a week, scientists used the Cassini orbiter to look at puffy
parts of Saturn's rings caught in white glare from the low-angle
lighting. Scientists have known about vertical clumps sticking out of
the rings in a handful of places, but they could not directly measure
the height and breadth of the undulations and ridges until Saturn's
equinox revealed their shadows.

"The biggest surprise was to see so many places of vertical relief
above and below the otherwise paper-thin rings," said Linda Spilker,
deputy project scientist at JPL. "To understand what we are seeing
will take more time, but the images and data will help develop a more
complete understanding of how old the rings might be and how they are
evolving."

The chunks of ice that make up the main rings spread out 85,000 miles
from the center of Saturn, but they had been thought to be only
around 30 feet thick in the main rings, known as A, B, C, and D.

In the new images, particles seemed to pile up in vertical formations
in each of the rings. Rippling corrugations -- previously seen by
Cassini to extend approximately 500 miles in the innermost D ring --
appear to undulate out to a total of 11,000 miles through the
neighboring C ring to the B ring.

The heights of some of the newly discovered bumps are comparable to
the elevations of the Rocky Mountains. One ridge of icy ring
particles, whipped up by the gravitational pull of Saturn's moon
Daphnis as it travels through the plane of the rings, looms as high
as 2.5 miles. It is the tallest vertical wall seen within the rings.

"We thought the plane of the rings was no taller than two stories of a
modern-day building and instead we've come across walls more than two
miles high," said Carolyn Porco, Cassini imaging team leader at the
Space Science Institute in Boulder, Colo. "Isn't that the most
outrageous thing you could imagine? It truly is like something out of
science fiction."

Scientists also were intrigued by bright streaks in two different
rings that appear to be clouds of dust kicked up in collisions
between small space debris and ring particles. Understanding the rate
and locations of impacts will help build better models of
contamination and erosion in the rings and refine estimates of their
age. The collision clouds were easier to see under the low-lighting
conditions of equinox than under normal lighting conditions.

At the same time Cassini was snapping visible-light photographs of
Saturn's rings, the Composite Infrared Spectrometer instrument was
taking the rings' temperatures. During equinox, the rings cooled to
the lowest temperature ever recorded. The A ring dropped down to a
frosty 382 degrees below zero Fahrenheit. Studying ring temperatures
at equinox will help scientists better understand the sizes and other
characteristics of the ring particles.

The Cassini spacecraft has been observing Saturn, its moons and rings
since it entered the planet's orbit in 2004. The spacecraft's
instruments have discovered new rings and moons and have improved our
understanding of Saturn's ring system.

The Cassini-Huygens mission is a cooperative project of NASA and the
European and Italian Space Agencies. JPL manages the mission for the
Science Mission Directorate at NASA Headquarters in Washington. JPL
also designed, developed and assembled the Cassini orbiter and its
two onboard cameras. The imaging team is based at the Space Science
Institute. The Composite Infrared Spectrometer team is based at
NASA's Goddard Space Flight Center in Greenbelt, Md.

To view Cassini images of the equinox and for more information about
the mission, visit:

http://www.nasa.gov/cassini

NASA Television's Video File also will air the images. For downlink,
scheduling information and streaming video, visit:

http://www.nasa.gov/ntv
        
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Received on Mon 21 Sep 2009 04:00:24 PM PDT