Giant volcanic eruption on Jupiter's moon Io
Observations by the Galileo spacecraft, made five months apart, have revealed a new dark spot on Jupiter's moon Io. It is about the size of the former East Germany and indicates dramatic volcanic activity at this time. "This is the largest surface change on Io observed by Galileo in its entire 2-year tour of the Jovian system," said Alfred McEwen, a member of Galileo's imaging team and a scientist at the University of Arizona in Tucson.
In June 1997, Galileo and the Hubble Space Telescope spotted a 121-kilometer plume of smoke over Pillan Patera-a volcanic center named after a South American god of thunder, fire, and volcanoes-and both Galileo as well as astronomers on Earth noticed a bright red spot. A comparison of images taken with a camera on board Galileo shows clear differences between the images from April 4, 1997 and those from September 19, 1997.
The change you can see now occurred in the five months between Galileo's seventh and tenth orbits around Jupiter. During this time, a large dark spot with a diameter of about 400 kilometers formed. It surrounds the Pillan Patera. Dark features in the center of the deposits could be new lava flows.
„Most volcanic deposits show up to us in white, yellow or red because of the sulphur. The new deposit, however, is grey. This tells us that it has a different composition and is possibly richer in silicates than the other regions,” explains McEwen. Scientists have long known that silicate volcanism occurs on Io and suspect that the moon is composed primarily of silicates. However, due to its pronounced volcanism, the composition of the silicates could be different than what is known from Earth. Examining them would then allow conclusions to be drawn about Io's development.
The Io images showing changes around Pillan Patera also reveal a change in the Pele deposit, the large red oval southwest of Pillan Patera. This may indicate that both volcanoes were active at the same time and influenced each other. A dark region southwest of Pele that appears to be similar to the Pillan deposits was already present when the Voyager probe flew by in 1979.
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