This is a composite of four THEMIS infrared images of two medium size volcanoes
and the surrounding area. The scene is located on the Tharis Platue north east
of Ascraeus Mons, one of the largest volcanoes in the solar system. There are a
number of fascinating features including impact craters, lava flows, and of
course volcanoes.
The earliest features still visible are the two volcanic cones. Sometime after the northern (upper) cone formed, it was hit by a large asteroid or comet on its northeastern flank. The crater was then flooded, as was the entire area, by lava flows emanating from Ascraeus Mons. These flows are what constitute the planes that are blanketing the area. There were further impacts and then some final eruptions from the two volcanic cones. One of the impacts is particularly interesting. It struck just north of the southern cone. What makes it interesting is the oval shape and the "butterfly" ejecta blanket surrounding it. This indicates that the object struck at a very shallow angle. It may very well have been a small moon whose orbit decayed and struck the planet. The innermost moon of Mars, Phobos, will do exactly that in the next several million years. The interest in this crater doesn't end there. It was also the target of one of the last flows from the volcano. Also notice that several of the impacts on and around the cones actually show ejecta on the flanks of the volcanoes. Some links Full Size JPeg ASU context Mars Global Surveyor / USGS context Olympus Mons - the Largest Volcano Known Visible Light Images of the Volcanic Cones: 
 
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