4. Viking Orbiter Mosaic (5°S,80°W)
This mosaic shows a global view of Mars as seen by NASA's Viking spacecrafts in the late 1970s. The linear structure stretching east-west across the center of the image is Valles Marineris, a very large trough system. The two brown, circular objects on the left side of the image are Pavonis Mons and Ascraeus Mons, two of the large shield volcanos in the Tharsis region (see slides #10 and #11). Most of the volcanic and tectonic activity on Mars in the last 3 billion years has been concentrated in the Tharsis region.
Image processing by U.S. Geological Survey