Promethei Terra is a large Martian region covering 3300 km at its broadest extent. It lies to the east of the massive Hellas basin. Like much of the southern part of the planet it is a heavily cratered, highland region. Promethei Terra was named for a classic

albedo feature In planetary geology, an albedo feature is a large area on the surface of a planet (or other Solar System body) which shows a contrast in brightness or darkness (albedo) with adjacent areas. Historically, albedo features were the first (and usu ...

of Mars, with the original name derived from that of the Greek god

Prometheus In Greek mythology, Prometheus (; , , possibly meaning "forethought")Smith"Prometheus". is a Titans, Titan. He is best known for defying the Olympian gods by taking theft of fire, fire from them and giving it to humanity in the form of technol ...

. Promethei Terra lies mostly in the

Hellas quadrangle The Hellas quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Hellas quadrangle is also referred to as MC-28 (Mars Chart-28). The Hellas quadrangle ...

of Mars.

Lobate debris aprons

One very important feature common in Promethei Terra are piles of material surrounding cliffs. These materials are called

lobate debris apron Lobate debris aprons (LDAs) are geological features on Mars, first seen by the Viking Orbiters, consisting of piles of rock debris below cliffs. These features have a convex topography and a gentle slope from cliffs or escarpments, which suggest fl ...

s (LDAs). Recently, research with the Shallow Radar on the

Mars Reconnaissance Orbiter The ''Mars Reconnaissance Orbiter'' (''MRO'') is a spacecraft designed to search for the existence of water on Mars and provide support for missions to Mars, as part of NASA's Mars Exploration Program. It was launched from Cape Canaveral on Au ...

has provided strong evidence that the LDAs are

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

s that are covered with a thin layer of rocks. Large amounts of water ice are believed to be in the LDAs. Available evidence strongly suggests this area accumulated snow in the past. When the tilt (obliquity) of Mars increases the southern ice cap releases large amounts of water vapor. Climate models predict that when this occurs water vapor condenses and falls where LDAs are located. The tilt of the Earth changes little because the relatively large Moon keeps it stable. The two tiny Martian moons do not stabilize its planet, so the rotational axis of Mars undergoes large variations. It has been known for some time that Mars undergoes many large changes in its tilt or obliquity because its two small moons lack the gravity to stabilize it, as the Moon stabilizes Earth; at times the tilt has even been greater than 80 degrees Lobate debris aprons may be a major source of water for future Mars colonists. Their major advantage over other sources of Martian water are that they can easily mapped from orbit and they are closer to the equator where crewed missions are more likely to land. Image:ESP_020319flowcontext.jpg, Context for the next image of the end of a flow feature, also called a lobate debris apron. It is probably a glacier. Location is Hellas quadrangle. Image:ESP_020319flowsclose-up.jpg, Close-up of the area in the box in the previous image. Possible terminal moraine of a glacier. For scale, the box shows the approximate size of a football field. HiRISE image. Image:20543 gap in crater rim.jpg, Material flowing through a crater rim. HiRISE image. Lateral moraines are labeled.

Glacier-like forms

Many formations are probably glaciers or the remains of old glaciers because they look so much like glaciers on the Earth. Image:ESP020886 with tongue shaped glacier.jpg, HiRISE image showing thin glacier on left. Glacier on the right is thick, containing ice under a thin layer of dirt and rock. Wikielephantglacier.jpg, Romer Lake's Elephant Foot Glacier in the Earth's Arctic, as seen by Landsat 8. This picture shows several glaciers that have the same shape as many features on Mars that are believed to also be glaciers. ESP 045505 1400flow.jpg, Flow feature that was probably a glacier. HiRISE image.

Gullies

Gullies occur on steep slopes, especially on the walls of craters. Gullies are believed to be relatively young because they have few, if any craters. Moreover, they lie on top of sand dunes which themselves are considered to be quite young. Usually, each gully has an alcove, channel, and apron. Some studies have found that gullies occur on slopes that face all directions, others have found that the greater number of gullies are found on poleward facing slopes, especially from 30-44 S. For years, many believed that gullies were formed by running water, but further observations demonstrate that they may be formed by dry ice. Recent studies describe using the High Resolution Imaging Science Experiment (HiRISE) camera on MRO to examine gullies at 356 sites, starting in 2006. Thirty-eight of the sites showed active gully formation. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes. In some years frost, perhaps as thick as 1 meter, triggers avalanches. This frost contains mostly dry ice, but also has tiny amounts of water ice. ESP 048881 1415gullies.jpg, Gullies in crater. HiRISE image. 48881 1415polygons.jpg, Close view of gullies in crater. Polygons are visible in this close view. HiRISE image.

Other scenes in Promethei Terra

Image:ESP_024868pyramid.jpg, Layered feature of unknown origin. HiRISE image. Image:28415facewide.jpg, HiRISE image of crater floor. The box indicates where the next picture is located. Image:28415grooves.jpg, Close-up of a portion of a crater wall indicated in the previous photo. There seems to be grooves in the wall.

References

External links