© Carolyn Porco and CICLOPS; NASA/JPL-Caltech/SSIAn image of Saturn taken in December 2010 by the Cassini spacecraft shows a storm with a latitudinal and longitudinal extent of 10,000 km and 17,000 km, respectively. The latitudinal extent of the storm’s head is approximately the distance from London to Cape Town. A "tail" emerging from its southern edge extends further eastward.
The Great White Spot on Saturn has been imaged in unprecedented detail and is now yielding clues to how this titanic storm may have formed far earlier than scientists expected.
The staggeringly powerful thunderstorm is approximately 6,200 miles (10,000 kilometers) wide, nearly as wide as Earth, and has a tail of white clouds that encircles all of Saturn.
The storm began forming in the ringed planet's northern hemisphere in December. This is about 10 years early for Great White Spots, which usually recur about every 30 Earth years, when Saturn's northern hemisphere tilts most toward the sun.
Only five similar Great White Spots have been observed in the past 135 years.
To learn more about this mystery storm, researchers employed both ground-based telescopes and observations from the Cassini spacecraft in orbit around Saturn. Their findings show it to be packing as much total energy as "the Earth receives from the sun within one year," said researcher Georg Fischer, a planetary scientist at the Austrian Academy of Sciences in Graz.
The Great White Spot is a massive complex of thunderstorms. Radio waves emitted by electrical discharges there reveal intense and nearly continuous lightning that, at the peak of the storm, can flash 10 times or more per second.
A key mystery regarding Great White Spots is where they get their energy from. Since the spots seem to occur seasonally, researchers had suggested they might be powered by the sun. However, peering into this latest Great White Spot revealed its cloud patterns make sense only if winds "extend deep into the 'weather layer' - a 250-kilometer-thick [155 miles] layer where the main clouds reside, where sunlight does not arrive," researcher Agustin Sánchez-Lavega, a planetary scientist at Higher Technical School of Engineering of Bilbao in Spain, told SPACE.com. "This points to the action of an internal heat source as the power for the winds."
Still, questions remain as to how solar heat might help trigger such gigantic storms. One possibility is that energy from the sun triggers atmospheric changes that directly influence the upward flow of heat from deep within Saturn, researchers say.
The researchers detailed their findings in the July 7 issue of the journal Nature.
Comment: Carolyn Porco, Cassini Imaging Team Leader, had this to say today, regarding the storm:
"July 6, 2011
Dear Friends and Colleagues,
Last December, a remarkable thing happened at Saturn. A massive,
hissing, lightning-producing storm violently erupted in the northern
mid-latitudes of Saturn's atmosphere and grew to gargantuan
proportions. By the end of January, it had wrapped itself entirely
around the planet, developing an enormous degree of wavy, even sensuous,
details, reminiscent of the clouds on Jupiter.
Today, a group of Cassini scientists has published its findings in the
scientific journal, Nature, deduced from an examination of information
gathered by several instruments on Cassini. Prior to the planet's
August 2009 northern vernal equinox, when the sun was shining in the
southern hemisphere, the location of all observed storm activity on
Saturn was a band encircling the planet at 35 degrees south latitude
that imaging scientists had dubbed 'Storm Alley'. Well, to our great
puzzlement, this new storm -- now 500 times larger than any previously
seen by Cassini at Saturn and 8 times the surface area of Earth -- has
erupted at 35 degrees /north/ latitude. The shadow cast by Saturn's
rings has a strong seasonal effect, and it is possible that the switch
to powerful storms now being located in the northern hemisphere is
related to the change of seasons and the changing position of Saturn's
ring shadow. But why the obvious hemispheric symmetry in storm eruption
exists is not yet known.
The storm is also a prodigious source of radio noise, which comes from
lightning deep in the planet's atmosphere. As on Earth, the lightning is
produced in the water clouds, where falling rain and hail generate
electricity. The mystery is why Saturn stores energy for decades and
releases it all at once. This behavior is unlike that at Jupiter and
Earth, which have numerous storms occurring at any one time.
Go to ...
http://ciclops.org
... to learn more about this fascinating and spectacular meteorological
phenomenon, to listen to the storm's electrostatic discharges, and to
read an updated Captain's Log.
Enjoy!
Carolyn Porco
Cassini Imaging Team Leader
Director, CICLOPS
Space Science Institute
Boulder, CO