November, 1999

A Closer Look at a Volcano on Io

These images taken by the Galileo spacecraft show a portion of Prometheus, an active volcano on Jupiter's moon Io. The top image is a recent high-resolution view. The bottom image is an older, lower-resolution color view.

NASA Planetary Photojournal #PIA02508
Image produced by University of Arizona

The high-resolution image was taken during a close flyby of Io on October 10, 1999. The image reveals the presence of a volcanic caldera. [A volcanic caldera, or crater, is the depression left after ground collapses during a volcanic eruption.] Scientists note similarities between the flow dynamics of Prometheus and the Kilauea volcano in Hawaii. However, Prometheus is a much larger volcano with its caldera measuring about 28 kilometers (17 miles) long by 14 kilometers (9 miles) wide compared to the caldera of Kilauea which measures 3x5 km (1.8x3 miles).

The caldera was not evident in previous, lower-resolution images but the close flyby of Io permitted Galileo to obtain images of up to 10 times greater resolution. The image covers an area 96 kilometers (60 miles) wide and 29 kilometers (18 miles) high and was taken 12,000 kilometers (7,500 miles) above the surface.


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Exploring The Planets

1999 National Air and Space Museum