JUPITER MOON TRANSFORMED SINCE VOYAGER MISSIONS.

Byline: John Noble Wilford The New York Times

When the Voyager 1 spacecraft flew by Jupiter in 1979, it made the striking discovery that the moon Io throbbed with erupting volcanoes spewing sulfur across its mottled orange and white landscape. Now the Galileo spacecraft, renewing Earth's Jovian explorations, has transmitted a photograph showing that volcanism has transformed much of Io's surface over the past 17 years.

One of the most prominent changes occurred in the moon's southern hemisphere surrounding a large active volcano named Masubi. New deposits of sulfur and sulfur dioxide frost vented during Masubi's eruptions have resurfaced much of the region, causing changes in the coloring and contours of the surface compared with conditions seen in pictures taken by the two Voyager spacecraft.

``The changes we are seeing on Io are dramatic,'' said Dr. Michael J.S. Belton, an astronomer at the National Optical Astronomical Observatories, in Tucson, Ariz., who is the leader of the Galileo project's photo interpretation team. ``The colors of material on the ground and their distribution has changed substantially since the Voyager flybys.''

Galileo's first picture of Io, taken June 25 at a range of 1.4 million miles, was made public Thursday by the Jet Propulsion Laboratory in Pasadena, where the mission is being directed for the National Aeronautics and Space Administration. Dr. Torrence V. Johnson, the chief project scientist, also reported on the findings Thursday at a meeting in Birmingham, England, of the Commission on Space Research, an international organization of space scientists.

The surface of Io (pronounced either EYE-oh or EE-oh) is often said to resemble a pizza. As far as scientists can tell, the moon is covered with volcanic deposits presumably containing some dark silicate rock along with various sulfur-rich compounds that give Io its distinctive yellow and deep orange colors. The volcano Masubi is a predominantly white feature, being coated with frosts of sulfur dioxide.

``The sulfur dioxide gas that drives the volcano makes a big plume, condenses, then paints the surface white,'' Belton said.

Several plumes of erupting volcanoes were detected in the Voyager photographs, but none has been identified in the new Galileo picture. The smallest objects that can be discerned in the Galileo picture are at least 14 miles in diameter. As Galileo keeps orbiting Jupiter, it is expected to take more pictures of Io from a closer range and thus give scientists an even more detailed look at the transforming effects of the virtually continuous volcanic activity there.