Galileo Finds Big Changes on Io

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Contact:  Mary Beth Murrill                                July 18, 1996

GALILEO FINDS BIG CHANGES ON JUPITER'S VOLCANIC MOON IO

A new image of Jupiter's volcanically active moon Io [pronounced "EYE-oh"or "EE-oh"] returned by NASA's Galileo spacecraft shows that significant changes have occurred on the moon since Io was observed 17 years ago by the exploratory NASA spacecraft Voyagers 1 and 2.

"The changes we are seeing on Io are dramatic," said Galileo camera team leader Dr. Michael J.S. Belton of the National Optical Astronomical Observatories in Tuscon, AZ. Io's landscape undergoes constant change due to numerous sulfur volcanoes that continually erupt across its mottled orange and white face, he said. "The colors of material on the ground and their distribution has changed substantially since the Voyager flybys of 1979," Belton said.

One of the most striking changes noted in the image are new deposits of sulfur and sulfur dioxide frost deposited from the volcano Masubi in Io's southern hemisphere. "The sulfur dioxide gas that drives the volcano makes a big plume, condenses, then paints the surface white," Belton said. Masubi was discovered as an active volcano during the Voyager encounters of Io.

Galileo's first color image of Io was taken June 25 at a range of 2.24 million kilometers (1.4 million miles) during the spacecraft's approach to Jupiter's largest moon, Ganymede. The smallest features that can be discerned in the new image of Io are approximately 23 kilometers (14 miles) in size, a resolution comparable to the best Voyager images of the same face of Io.

Galileo promises to return new views of volcanic activity on Io throughout the spacecraft's remaining 17-month mission orbiting Jupiter. Higher resolution images of Io will be taken in coming months.

Launched in October 1989, Galileo entered orbit around Jupiter on December 7, 1995. The spacecraft's mission is to conduct detailed studies of the giant planet, its largest moons and the Jovian magnetic environment. The Jet Propulsion Laboratory (JPL), Pasadena, Calif., manages the mission for NASA's Office of Space Science, Washington, DC.

The Io image and other imagery and data received from Galileo has been posted to the World Wide Web, on the Galileo mission home page at:

http://www.jpl.nasa.gov/galileo.

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