First Ultraviolet Imaging Spectrograph (UVIS) Spectral Images of Jupiter

October 20, 2000

On 1 October 2000, the NASA/ESA Cassini spacecraft on its
way to Saturn started observations of the planet Jupiter.
The first data from the Ultraviolet Imaging Spectrograph
(UVIS) clearly show the planet's aurora and a glowing
ring of gas ejected from Jupiter's moon Io. This donut of
atoms is known as the Io torus.

Our pictures are the first published imaging spectroscopy
of the torus, although it was first discovered by Earth
telescopes and later studied by spacecraft, including the
Voyager and Galileo missions to Jupiter.

The UVIS images show multiple overlapping exposures of
this torus, each in the characteristic light emitted by
sulfur and oxygen atoms. All of these emissions are
invisible to the naked eye and can only be seen in the
ultraviolet light that the CU telescopes detect. We see
the entire donut of glowing gas in all its invisible

In these first observations, the Cassini spacecraft
stared at Jupiter for an entire rotation of its
atmosphere, that is, one Jupiter "day." Because the atoms
giving off the light are trapped by Jupiter's tilted
magnetic field, the torus wobbles back and forth during
the Jupiter day.

In the next 6 months, UVIS will continue to observe
Jupiter, the Io torus, and Jupiter's moons and aurora as
the Cassini spacecraft speeds toward Saturn. It will
arrive on 1 July 2004, drop a European-built probe to
land on Saturn's moon Titan, and observe Saturn and its
moons and rings from orbit for at least 4 years.

First Ultraviolet Imaging Spectrograph image

This image sums 36 exposures of the Io torus in the
emissions from sulfur and oxygen, taken over a 10-hour
period beginning on 3 October. The hydrogen emissions
from the Jupiter aurora form a central band to the right
side. The brightest areas represent the strongest
emissions of ionized sulfur and oxygen.

One day in the life of Jupiter's Io torus,
a donut of glowing gas from the moon Io's volcanic
eruptions. Each tilted line shows one type of ionized
atom in the torus. In one Jupiter day, the torus wobbles
back and forth once.

First UVIS animated spectral image

Cassini 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, Calif., manages the
Cassini mission for NASA's Office of Space Science, Washington, D.C.

For more information, contact:

Larry W. Esposito 303-492-5990

A. Ian F. Stewart 303-492-4630

Laboratory for Atmospheric and Space Physics

University of Colorado, Boulder, Colorado


Additional information about Cassini is available online at:

The Cassini spacecraft is scheduled to arrive at Saturn in July 2004 to
begin a four-year exploration of the ringed planet and its moons. The
Cassini mission is managed by NASA's Jet Propulsion Laboratory in Pasadena,
Calif., for NASA's Office of Space Science, Washington, D.C. JPL is a
division of the California Institute of Technology in Pasadena.

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