Fall Comes To Saturn Only Once Every 29.7 Years
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, CA. "This is among
the most important events Cassini has shown us."
On August 11th, 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 was Tuesday, when the
sun shone 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."
Saturn's Rings At Equinox Photo Credit
NASA
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.
Saturn's Rings At Equinox Photo Credit
NASA
"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, CO.
"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.
Saturn's Rings At Equinox Photo Credit
NASA
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.