Donald Savage
Headquarters, Washington April 8, 2004
(Phone: 202/358-1727)

Carolina Martinez
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-9382)

Heidi Finn
Cassini Imaging Central Laboratory, Boulder, Colo.
(Phone: 720/974-5859)

RELEASE: 04-119

TWO STORMS CAUGHT IN THE ACT ON SATURN

Three months before Saturn arrival, the Cassini
spacecraft caught two storms in the act of merging into one
larger storm. This is only the second time this phenomenon
has been observed on the ringed planet.

"Merging is one of the distinct features of storms in the
giant planet atmospheres," said Dr. Andrew Ingersoll, member
of the Cassini imaging team and professor of planetary
science at the California Institute of Technology in
Pasadena, Calif.

"On Earth, storms last for a week or so and usually fade away
when they enter the mature phase and can no longer extract
energy from their surroundings. On Saturn and the other giant
planets, storms last for months, years, or even centuries.
Instead of simply fading away, many storms on the giant
planets end their lives by merging. How they form, however,
is still uncertain," Ingersoll said.

With diameters close to 1,000 kilometers (621 miles), both
storms were seen moving west, relative to the rotation of
Saturn's interior, for about a month before they merged on
March 19-20, 2004.

The northern storm moved about twice as fast as the southern
storm, 11 meters versus 6 meters per second (25 vs. 13 mph)
respectively. They approached each other like two cars on a
highway and spun around each other in a counterclockwise
direction as they merged. This is the opposite of how
hurricanes spin in the southern hemisphere on Earth.

Just after the merger, on March 20, the new storm was
elongated in the north-south direction, with bright clouds on
either end. Two days later the storm settled into a more
circular shape and the bright clouds were spread around the
circumference to form a halo. Whether the bright clouds are
particles of a different composition or simply at a different
altitude is uncertain.

Although these storms moved slowly west, others at Saturn's
equator move east at speeds up to 450 meters per second
(1,000 miles per hour). That is about 10 times the speed of
Earth's jet streams and three times greater than the
equatorial winds on Jupiter.

"Saturn is the windiest planet in the solar system,"
Ingersoll said. "And that's a huge mystery. We'll be getting
closer to the planet all the way through June, so maybe we'll
find out," he said.

Images from the Voyager spacecraft flybys of Saturn in August
1981 show storms partially merging. But to see them with
Cassini, this far out from Saturn, is a mouthwatering
surprise to scientists, because they will get even closer
during the spacecraft's four-year Saturn tour. "I'm
optimistic because these images are already so good. The best
is yet to come," Ingersoll said.

The Cassini-Huygens mission is a cooperative project of NASA,
the European Space Agency and the Italian Space Agency. The
Jet Propulsion Laboratory (JPL), a division of the California
Institute of Technology in Pasadena, manages the Cassini-
Huygens mission for NASA's Office of Space Science,
Washington. The Cassini orbiter, including the two cameras
onboard the spacecraft, was designed, developed and assembled
at JPL. The imaging team is based at the Space Science
Institute, Boulder, Colo.

A series of Cassini images documenting this event is
available on the Internet at:

http://saturn.jpl.nasa.gov

http://ciclops.org

-end-