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Click for larger view Phobos is the larger of the two heavily-cratered Martian moons and is dominated by three large craters. The largest of Phobos' craters, Stickney, was named after the wife of Asaph Hall, the astronomer who discovered the moons of Mars. Stickney crater is 10 km in diameter, which is almost half of the average diameter of Phobos! The crater is so large relative to the size of Phobos that the satellite probably came close to breaking up. Radiating away from Stickney are sets of parallel grooves or striations. These fractures undoubtably formed as a result of the impact that produced Stickney.

Another interesting feature about Phobos is the duration of its orbit. Phobos revolves around Mars at an astounding rate. In fact, it revolves around Mars 3 times during one Martian day! As a result, Phobos appears to rise in the west, and set in the east!

Click for larger view

Click for larger view

Click for larger view
Viking 1 image of Phobos. The linear features and crater chains from lower left to upper right are believed to be results of the impact which formed Stickney crater. Viking 1 image of Stickney crater, the largest crater on Phobos. Stickney is about10 km in diameter and was formed by a giant impact. Note the striations to the right of the image leading away from the crater. Viking 1 image of Hall crater on
Phobos. The crater is 6 km in diameter. Just to the lower right of the crater is Phobos' south pole.