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

[Ron Baalke]

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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