Astronomy Picture of the Day
January 17, 2013

Tohil Mons and surroundings
Tohil Mons and surroundings

Credits: NASA/JPL/Univ. of Arizona - Galileo Project - Credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/IPF

Dramatic shadows extending across a Mountainous Landscape on Jupiter's volcanic moon Io reveal extremely interesting details of the topography around a Peak named Tohil Mons, well visible in the center of this mosaic created from images taken by the NASA - Galileo Spacecraft in October 2001.

According to the analysis carried out on stereo imaging of this relief (which has been pictured several times by Galileo during a few earlier Fly-Bys of Io), Tohil Mons rises approx. 5,4 Km (such as about 18.000 feet) above Io's Surface. However, the best images of Tohil Mons, with a resolution of 327 meters (such as 1070 feet) per picture element, were taken when the Sun was low in the Sky of Io, and therefore fit to produce "informative" shadows. North is toward the top of the mosaic and the Sun illuminates the Surface from the upper right. The various Topographic Features visible in the mosaic include a relatively straight Ridge extending South/West from the Peak, approx. 500- to 850-meters-high (such as about 1640- to 2790-foot-high); several Cliffs to the North/West and a bizarre-looking Pit (probably, in our opinion, as IPF, a small Collapse Pit OR - and we say most likely - just an optical/visual illusion, caused by the presence of a very dark and unusually shaped shadow!) that is located immediately to the East of the Peak.

Major questions remain about how Io's Mountains formed and how they are related to Io's ubiquitous Volcanoes. In fact, although Io - as you know - is more than extremely active volcanically, just a few of its Mountains appear to be actual Volcanoes. However, two Volcanic Craters (---> Calderae) do lie directly to the North/East of Tohil's Peak: a smaller dark-floored one, and a larger one at the very edge of the mosaic. Furthermore, the shape of the Pit located directly to the East of the Peak, also suggests a possible (and plausible) Volcanic Origin. Galileo Scientists used these images to investigate the Geologic History of Tohil Mons and its relationship to its neighboring Volcanic Features but, so far, no major insights have been reached about this topic. The image-mosaic is centered at 28° South Latitude and 161° West Longitude.

This picture (which is an Original NASA - Galileo Orbiter b/w image mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 03600) has been additionally processed and then colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Galileo Orbiter and then looked down, towards the Surface of the Jovian moon Io), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements present on the Surface of Io, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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