SETI bioastro: Cassini Captures Light Show On Jupiter's Moon, Io, During Eclipse

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From: Larry Klaes (
Date: Thu May 31 2001 - 15:12:13 PDT

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Sent: Thursday, May 31, 2001 5:08 PM
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Subject: Cassini Captures Light Show On Jupiter's Moon, Io, During


Lori Stiles, University of Arizona News Services, 520-621-1877
May 31, 2001

The Cassini spacecraft, passing through the Jupiter system on Jan. 1, 2001,
en route to Saturn, recorded a sequence of images showing Jupiter's moon Io
glowing in the darkness of the giant planet's shadow.

University of Arizona planetary scientist Paul Geissler presented a color
version of this "movie" today at the American Geophysical Union meeting in
Boston. The movie shows details of moon's visible aurorae that solve some of
the puzzles presented by the Galileo spacecraft observations, Geissler said.

The new animation is available online from the Cassini Imaging Science team
at the University or Arizona, Tucson, at
and from NASA's Jet Propulsion Laboratory, Pasadena, Calif., at

Little was known about these dazzling light shows before the Galileo
spacecraft arrived at the Jupiter system in late 1995. Galileo pictures of
Io in eclipse showed a colorful display of red, greenish and blue emissions
bright enough to be seen with the naked eye. These glows are due to various
gases in Io's tenuous atmosphere that are excited by electrical currents,
much like the Aurora Borealis on Earth.

Galileo could send back only a few snapshots because of its nonfunctional
radio antenna, and these pictures were taken in only six colors, so it was
impossible to be sure of the exact composition of the glowing gases. From
ground-based telescopes and Hubble Space Telescope observations it was
believed that the red glow was caused by neutral atomic oxygen and that
sodium was the source of the greenish glow. The blue glow was unidentified,
but suspected to be sulfur dioxide.

Although the Cassini spacecraft did not come as close to Io as did the
Galileo spacecraft, Cassini could stare at Io for two hours at a time and
record sequences of images ("movies") of entire eclipses, Geissler said.
Cassini's camera is also sensitive to shorter wavelengths than is Galileo's
camera, and it could record more colors using different filters. Cassini
caught Io's aurorae in motion and detected emissions at previously unknown
wavelengths. Both red atomic oxygen and blue molecular sulfur dioxide
emissions are seen in the Cassini images, along with thermal glows from hot
lava at several active volcanoes.

The motion of the aurorae suggests that the visible emissions are powered by
electrical currents that connect Io to Jupiter, similar to the ultraviolet
aurorae seen on Io by the Hubble Space Telescope. A volcanic plume erupting
on the opposite side of Io can just be detected over the moon's north pole.
This eruption left an enormous red ring around the volcano Tvashtar, seen
erupting by both Galileo and Cassini, Geissler noted. These results tell us
more about the patchy atmosphere of Io and the electrical currents that
excite the visible emissions, he added.

*** (EDITORS: UA planetary sciences Professor Alfred McEwen, a member of the
Cassini Imaging Science team as well as the Galileo Imaging Science team, is
also a contact on this story. He can be reached today in Tucson at
520-621-4573 or 520-320-5766.

Contact Information
Paul Geissler

Alfred McEwen

***The Jet Propulsion Laboratory Media Relations Office today is releasing
news stories and image advisories the Io Color Eclipse Movie. The JPL Media
Relations Office contact Guy Webster, 818- 354-6278, is at the AGU meeting
is Boston.)****

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