Galileo I32 Tohil Mosaic

I finally uploaded the final Galileo SSI observation that I had not completed to my Galileo Io Images Page. The mosaic, from Galileo's October 2001 I32 flyby of Io, is from the 32ISTOHIL_01 observation and covers the central part of Tohil Patera and Tohil Mons and almost all of the smaller Radegast Patera. The images in this mosaic were acquired shortly after these features passed the morning terminator and the sun was low in the ionian sky, making topography appear more visible. This mosaic has a resolution of 50.9 meters per pixel. Definitely check out the full-resolution version.

Tohil Mons is a 9.4-km tall mountain with a very complex morphology. It appears to consist of slabs of Io's lithosphere that have been thrust upward through a series of thrust fault, similar to imbricate thrust belts on Earth. While no direct evidence for layering is visible on the slopes of Tohil Mons (layers would need to be much thicker than the expected 1-10 m thick flows thus far observed on Io to be visible here), indirect evidence comes from several patches of bright frost visible along many slope faces. These patches are likely SO₂ frost deposited after sapping. The complex morphology of the mountain is largely the result of mass wasting since the mountains formation, including landslides and massive slope failure, particularly near the top of the mountain.

The two volcanoes visible in this mosaic have quite different morphologies. Radegast Patera, a small volcano visible across much of the center frame, has a dark floor and steep sides. Two dark lava flows are visible near the northern end of Radegast. These flows formed sometime between February 2000 and October 2001 and, according to the NIMS instrument onboard Galileo, were still warm during the I32 encounter. The lack of debris flows on the patera floor suggests that either the volcano is or was a lava lake or that the rate of resurfacing out paces that of mass wasting. Tohil Patera, a much larger volcano that covers much of the two right-hand frames, is much shallower depression with a mottled appearance. The brighter portions of the patera appears to be covered in ~10 meter thick flows, either sulfur flows or older silicate flows that are now coated in SO₂. Several dark patches are visible with some due to dark, silicate flows.

A more extensive overview of this observation is provided in Turtle et al. 2004 and Williams et al. 2004.

Link: Galileo I32 Images [pirlwww.lpl.arizona.edu]