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 colors.

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.

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.

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