Mars Global Surveyor
Mars Orbiter Camera

Parallel Ridges with Rough Texture and Residual Frost

This picture shows a set of parallel ridges trending from upper left to lower right, spaced about 250-500 meters (273-547 yards) from one another. The amplitude of these ridges is not known, but elsewhere they are less than 20 m (66 ft) high. The surface also has irregular, light-toned knobs that resemble large boulders or pinnacles.

Parallel Ridges and Mounds with Gullies and Irregular Pits

A large portion of the landing ellipse (and the majority of the area seen in this image) is covered by parallel ridges surmounted by isolated groups of gullies and pits. The gully systems typically extend less than 500 meters (547 yards), and are often only a few hundred meters across. These gullies do not show the integration normal for fluid erosion (i.e., they were not carved by running water); instead, they have the form of cracks and depressions expanded by wall- and head-enlargement by processes such as sapping (removal of wall support by fluid seepage or the evaporation of ground ice) or ablation (removal of ices by sublimation and wind).

Low Relief with Subtle Depressions and Small Knobs

Some areas show little or no topographic relief (i.e., the area is relatively flat with no hills, ridges, or gullies). One class of this type of surface displays small, subtle, isolated depressions and areas of the rough texture made up of light-toned patches of knobs that resemble large boulders or pinnacles.

Dark Sand Dunes and Bright Low Relief Surface with Gullies

The darkest surface in the landing ellipse, now seen without its seasonal bright frost cover, shows the unmistakable form of dark sand dunes. This image shows the margin of the dune field that crosses the center of the MOC image. Note that in some places the sand depth is shallow and the shape and slopes of the underlying features can be seen.

Weakly-organized Ridges/Mounds and Gullies/Depressions

The second-most abundant surface texture in this portion of the landing ellipse consists of poorly aligned ridges and depressions which occassionally display steep wall slopes. This surface appears rugged at the scale of tens of meters, but may be smoother at small scales (meters).

Smooth Surface with Occassional Ridges and Pits

The southern-most portion of the November 26th MOC image shows a pattern of small, isolated ridges and a few irregular depressions and pits. However, much of the surface is actually quite smooth compared to other portions of the landing ellipse.

Representative Features of the Central Landing Ellipse

This illustration shows a summary of the landforms seen within the November 26th MOC image in different colors. It is clear that the smoothest surface (green at bottom of frame) is rare in this part of the landing ellipse. Sand dunes (black) and really rough terrain (orange) are also fairly rare. Much of the surface is ridged with either gullies or pits.