NASA Spacecraft
Tracks Raging Saturn Storm
(29 April 2008) As a powerful
electrical storm rages on Saturn with lightning bolts 10,000 times more
powerful than those found on Earth, the Cassini spacecraft continues its
five-month watch over the dramatic events.
Scientists with
NASA's Cassini-Huygens mission have been tracking the visibly bright,
lightning-generating storm--the longest continually observed electrical storm
ever monitored by Cassini.
Saturn's electrical storms resemble
terrestrial thunderstorms, but on a much larger scale. Storms on Saturn have
diameters of several thousand kilometres (thousands of miles), and radio
signals produced by their lightning are thousands of times more powerful than
those produced by terrestrial thunderstorms.
A bright, powerful, lightning-producing storm churns and coasts along the lane of Saturn's southern hemisphere nicknamed "Storm Alley" by scientists. NASA's Cassini spacecraft detected this particular tempest after nearly two years during which Saturn did not appear to produce any large electrical storms of this kind. The storm appears as a bright, irregular splotch on the planet near lower right. Lightning flashes within the persistent storm produce radio waves, called Saturn Electrostatic Discharges, which the Cassini radio and plasma wave science instrument first detected on Nov. 27, 2007. Cassini's imaging cameras then spotted the storm, taking the images used to create this color view about a week later on Dec. 6. This electrical storm is similar in appearance and intensity to those previously monitored by Cassini. All of these powerful electrostatic producing storms appeared at about 35 degrees south latitude on Saturn. This storm has now been continuously tracked by Cassini for several months, whereas previous storms observed by the spacecraft lasted for less than 30 days: See Saturn's Long-lived Storm for images of the storm acquired three months after this view. The view looks toward the un-illuminated side of the rings from about 5 degrees above the ringplane. Tethys (1,071 kilometers, or 665 miles across) is seen here in the foreground, and casts its shadow onto the high northern latitudes. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft wide-angle camera at a distance of approximately 1.7 million kilometers (1 million miles) from Saturn. (courtesy: NASA/JPL/Space Science Institute)
Lightning flashes within the persistent
storm produce radio waves called Saturn electrostatic discharges, which the
radio and plasma wave science instrument first detected on Nov. 27, 2007.
Cassini's imaging cameras monitored the position and appearance of the storm,
first spotting it about a week later, on Dec. 6.
"The electrostatic
radio outbursts have waxed and waned in intensity for five months now," said
Georg Fischer, an associate with the radio and plasma wave science team at the
University of Iowa, Iowa City. "We saw similar storms in 2004 and 2006 that
each lasted for nearly a month, but this storm is longer-lived by far. And it
appeared after nearly two years during which we did not detect any electrical
storm activity from Saturn."
The new storm is located in Saturn's
southern hemisphere--in a region nicknamed "Storm Alley" by mission
scientists--where the previous lightning storms were observed by
Cassini.
"In order to see the storm, the imaging cameras have to be
looking at the right place at the right time, and whenever our cameras see the
storm, the radio outbursts are there," said Ulyana Dyudina, an associate of the
Cassini imaging team at the California Institute of Technology in Pasadena,
Calif.
Cassini's radio plasma wave instrument detects the storm every
time it rotates into view, which happens every 10 hours and 40 minutes, the
approximate length of a Saturn day. Every few seconds the storm gives off a
radio pulse lasting for about a tenth of a second, which is typical of
lightning bolts and other electrical discharges. These radio waves are detected
even when the storm is over the horizon as viewed from Cassini, a result of the
bending of radio waves by the planet's atmosphere.
Amateur astronomers
have kept track of the storm over its five-month lifetime. "Since Cassini's
camera cannot track the storm every day, the amateur data are invaluable," said
Fischer. "I am in continuous contact with astronomers from around the
world."
The long-lived storm will likely provide information on the
processes powering Saturn's intense lightning activity. Cassini scientists will
continue to monitor Storm Alley as the seasons change, bringing the onset of
autumn to the planet's southern hemisphere.
The Cassini-Huygens mission
is a co-operative project of NASA, the European Space Agency and the Italian
Space Agency. JPL, a division of Caltech, manages the Cassini mission for
NASA's Science Mission Directorate, Washington, D.C. 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. The radio
and plasma wave science team is based at the University of Iowa, Iowa
City.
(source: NASA Jet Propulsion Laboratory)
