Scientists pointed NASA's Galileo spacecraft camera at the Tohil region of Jupiter's moon Io to investigate the curious relationship between Io's mountains and its volcanoes.
This mosaic of Galileo images taken Oct. 16, 2001, shows details of the mountain called Tohil Mons (lower left), a small dark-floored volcanic crater, or "patera," bordered by mountain walls (middle), and intricate patterns of dark lava flows intertwined with bright material on the floor of a larger crater, Tohil Patera (upper right). An earlier stereo observation by Galileo revealed that Tohil Mons rises up to 6 kilometers (19,700 feet) above the surrounding plains. In contrast, shadows in the new images indicate the two paterae are only about 100 meters (330 feet) deep.
The new images were taken soon after sunrise at Tohil, with a resolution of 50 meters (160 feet) per picture element to reveal details never seen before. Another view showing the entire mountain at lower resolution was also acquired.
Despite Io's extremely high rate of volcanic activity, its mountains do not resemble volcanoes seen elsewhere in the solar system. Instead, the mountains appear to be formed by the uplift of large blocks of Io's crust. This image shows evidence of numerous landslides from the mountain (bottom left). However, one of the most surprising revelations from this observation is that despite the closeness of the small, dark-floored patera to the mountain walls, the patera floor is not covered with any landslide debris. This indicates that the patera floor has been resurfaced with lava more recently than any landslides have occurred. Another possibility is that this patera, like others on Io, is actually a lava lake and completely consumes debris that falls into it from the mountain. Galileo's infrared-mapping instrument has detected heat from the patera, indicating an active or very recent eruption.
North is to the top of the picture and the Sun illuminates the surface from the right. The mosaic is centered at 27.5 degrees south latitude and 160 degrees west longitude and covers 280 kilometers (170 miles) from upper right to lower left.
The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. Additional information about Galileo and its discoveries is available 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://solarsystem.nasa.gov/galileo/gallery/index.cfm.