Four views of the hemisphere of Io which faces Jupiter showing changes seen
on June 27th, 1996 by the Galileo spacecraft as compared to views seen by
the Voyager spacecraft during the 1979 flybys. Clockwise from upper left is
a Voyager 1 high resolution image, a Voyager 1 color image, a Galileo color
image, and a Voyager 2 color image. North is to the top of the picture.
Voyager and Galileo images have been adjusted to provide comparable color
balances similar to Voyager color. The most dramatic changes between
Voyagers 1 and 2, just 4 months apart, were the effects of the eruptions of
Surt (latitude +45 degrees) and Aten Patera (latitude -48 degrees) which
darkened the caldera floors and left diffuse pyroclastic deposits covering
areas about 1400 km in diameter (about the size of Alaska). In the Galileo
image the Surt and Aten regions appear much more similar to the Voyager 1
pre-eruption images than to the Voyager 2 images. The plume deposits appear
to have largely "faded away" and the calderas have brightened. The Surt and
Aten plume deposits had spectral properties similar to the plume deposits of
Pele. Pele's deposits have not faded, suggesting that Pele had remained
intermittently active whereas Surt and Aten are only rarely active.

The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's
Office of Space Science, Washington, DC.