Non-active dunes in the Acheron Fossae region of Mars between the Viking and Mars Global Surveyor eras

Comparison of a high resolution Viking image (422B10; 8 m/pixel) with a Mar s Orbiter Camera image (SP2-502/06; 5.6 m/pixel) of dunes in the Acheron Fo ssae region of Mars (38 degrees N, 135 degrees W) reveals that the dunes mo ved <1 pixel during a span of almost 21 Earth years. Very shallow illuminat ion in the MOC image indicates the dunes are <1.5 m high. The images indica te that any movement of these Martian dunes is <0.4 m/yr, a rate that is le ss than the documented movement of comparable dunes on Earth by a factor of up to 200. The Acheron Fossae dunes occur within a region of low thermal i nertia, indicating that the dunes may be stabilized by a pervasive dust cov er. Alternatively, the saltation threshold was not exceeded significantly a t this location in more than 20 years.