This stereo image of Tvashtar, Catena on Jupiter's moon Io, was created by combining two different views of Tvashtar taken by NASA's Galileo spacecraft on November 25, 1999 (shown in red) and February 22, 2000 (shown in blue). It illustrates the topography of the region. The volcanic depression, or caldera, in the center of the image, is surrounded by a raised plateau. To the northeast of the main caldera, the plateau's inner and outer margins are scalloped, which may indicate that a process called sapping is eroding them. Sapping occurs when fluid escapes from the base of a cliff, causing the material above it to collapse. Smaller calderas have formed in the floor of the main caldera. This nesting of calderas is also observed on Earth, at Kilauea in Hawaii. (The two bright red regions roughly triangular in shape, toward the upper left of the image are where the earlier image was overexposed by hot lava fountains).

Galileo scientists are in the process of generating topographic maps from these images. Such maps will reveal the heights and slopes of different landforms in this region which will help scientists to determine the properties, such as strength, of Io's surface materials. They will also be useful in understanding the processes of uplift and erosion on Io.

The picture is centered at 59 degrees north latitude and 121 degrees west longitude. North is to the top of the picture and the sun illuminates the surface from the lower left. The observations used to make the stereo image were made at ranges of 18,000 and 34,500 kilometers (11,400 and 21,600 miles) from Io. The resolution of the stereo image is about 320 meters (350 yards) per picture element.

Image produced by: Moses Milazzo, Planetary Image Research Lab. (PIRL), Lunar and Planetary Lab. (LPL), University of Arizona

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA.

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at http://galileo.jpl.nasa.gov/. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/images/io/ioimages.html.

NASA's Planetary Photojournal PIA-02552

May 31, 2000