Phobos Over Mars . ... Credit Copyright: Viking Project , JPL NASA Explanation: Hurtling through space a mere 3,000 miles above the Martian surface , the diminutive moon Phobos (below and left of center) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977. This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself is 5,000 miles below the Orbiter. ... NASA Official: Jay Norris. ...