New fire on Io.

Jupiter's moon Io has a new black eye. The huge dark spot, 400 kilometers in diameter, surrounds the volcano Pillan Patera and probably represents debris that rained down on the surface from an active plume. The darkest, sinewy features at the center of the deposit may be fresh lava flows.

The Galileo spacecraft first imaged the spot in September. The feature, which was not present when the craft viewed the same region in April, represents the largest change that Galileo has ever recorded on this volcanically active moon.

In June, both the craft and the Hubble Space Telescope recorded what now appears to be the source of the debris: a 120-km-high plume emanating from Pillan Patera.

Most plume deposits on Io show up as white, yellow, or red--colors typical of sulfur. The new deposit is gray, indicating that it is probably richer in silicates than the other volcanic debris, says Galileo scientist Alfred S. McEwen of the University of Arizona in Tucson.

Although the high temperatures on Io suggest that silicate, a kind of volcanic rock found on Earth, should be common on this Jovian moon, the fresh plume debris offers the first visual evidence of such material, says McEwen. Infrared spectra of the debris, taken by another Galileo instrument, indicate that the material is either silicate or iron pyrite, commonly known as fool's gold, says Robert W. Carlson of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The Io image, which NASA released in early November, also reveals changes in the color and distribution of material surrounding the well-known volcano Pele, which lies about 400 km southwest of Pillan. Both volcanoes may have erupted at the same time, and their plumes could have interacted.