Cassini Captures Ghostly Dance Of Saturn's Northern Lights

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http://www.jpl.nasa.gov/news/news.cfm?release=2009-176

Cassini Captures Ghostly Dance Of Saturn's Northern Lights
Jet Propulsion Laboratory
November 24, 2009

PASADENA, Calif. - In the first video showing the auroras above the
northern latitudes of Saturn, Cassini has spotted the tallest known
"northern lights" in the solar system, flickering in shape and
brightness high above the ringed planet.

The new video reveals changes in Saturn's aurora every few minutes, in
high resolution, with three dimensions. The images show a previously
unseen vertical profile to the auroras, which ripple in the video like
tall curtains. These curtains reach more than 1,200 kilometers (750
miles) above the edge of the planet's northern hemisphere.

The new video and still images are online at:
http://www.nasa.gov/cassini , http://saturn.jpl.nasa.gov and
http://ciclops.org .

Auroras occur on Earth, Jupiter, Saturn and a few other planets, and the
new images will help scientists better understand how they are generated.

"The auroras have put on a dazzling show, shape-shifting rapidly and
exposing curtains that we suspected were there, but hadn't seen on
Saturn before," said Andrew Ingersoll of the California Institute of
Technology in Pasadena, who is a member of the Cassini imaging team that
processed the new video. "Seeing these things on another planet helps us
understand them a little better when we see them on Earth."

Auroras appear mostly in the high latitudes near a planet's magnetic
poles. When charged particles from the magnetosphere -- the magnetic
bubble surrounding a planet -- plunge into the planet's upper
atmosphere, they cause the atmosphere to glow. The curtain shapes show
the paths that these charged particles take as they flow along the lines
of the magnetic field between the magnetosphere and the uppermost part
of the atmosphere.

The height of the curtains on Saturn exposes a key difference between
Saturn's atmosphere and our own, Ingersoll said. While Earth's
atmosphere has a lot of oxygen and nitrogen, Saturn's atmosphere is
composed primarily of hydrogen. Because hydrogen is very light, the
atmosphere and auroras reach far out from Saturn. Earth's auroras tend
to flare only about 100 to 500 kilometers (60 to 300 miles) above the
surface.

The speed of the auroral changes in the video is comparable to some of
those on Earth, but scientists are still working to understand the
processes that produce these rapid changes. The height will also help
them learn how much energy is required to light up auroras.

"I was wowed when I saw these images and the curtain," said Tamas
Gombosi of the University of Michigan in Ann Arbor, who chairs Cassini's
magnetosphere and plasma science working group. "Put this together with
the other data Cassini has collected on the auroras so far, and you
really get a new science."

Ultraviolet and infrared instruments on Cassini have captured images of
and data from Saturn's auroras before, but in these latest images,
Cassini's narrow-angle camera was able to capture the northern lights in
the visible part of the light spectrum, in higher resolution. The movie
was assembled from nearly 500 still pictures spanning 81 hours between
Oct. 5 and Oct. 8, 2009. Each picture had an exposure time of two or
three minutes. The camera shot pictures from the night side of Saturn.

The images were originally obtained in black and white, and the imaging
team highlighted the auroras in false-color orange. The oxygen and
nitrogen in Earth's upper atmosphere contribute to the colorful flashes
of green, red and even purple in our auroras. But scientists are still
working to determine the true color of the auroras at Saturn, whose
atmosphere lacks those chemicals.

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, manages the mission for the Science Mission Directorate at
NASA Headquarters in Washington. 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.

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui...@jpl.nasa.gov

Joe Mason 720-974-5859
Space Science Institute, Boulder, Colo.
jma...@ciclops.org

2009-176