Scalloped topography
Encyclopedia
Scalloped topography is common in the mid-latitudes
of Mars, between 45° and 60° north and south. It is particularly prominent in the region of Utopia Planitia
, , in the northern hemisphere, and in the region of Peneus
and Amphitrites Patera in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in insolation
. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation (direct transition of a material from the solid to the gas phase with no intermediate liquid stage). This process may still be happening at present. In Utopia Planitia, a series of curvilinear ridges parallel to the scarp are etched on the floor of large scalloped depressions, possibly representing different stages of scarp erosion. Sometimes the surface around scalloped terrain or scalloped topography displays "patterned ground
", characterized by a regular pattern of polygonal fractures. These patterns indicate that the surface has undergone stress, perhaps caused by subsidence, desiccation, or thermal contraction. Such patterns are common in periglacial
areas on Earth. Scalloped terrains in Utopia Planitia display polygonal features of different sizes: small (abut 5–10 m across) on the scarp, and larger (30–50 m across) on the surrounding terrains. These scale differences may indicate local difference in ground ice concentrations.
Mid-latitudes
The mid-latitudes are the areas on earth between the tropics and the polar regions, approximately 30° to 60° north or south of the equator. The mid-latitudes are an important region in meteorology, having weather patterns which are generally distinct from weather in the tropics and the polar...
of Mars, between 45° and 60° north and south. It is particularly prominent in the region of Utopia Planitia
Utopia Planitia
Utopia Planitia is the largest recognized impact basin on Mars with an estimated diameter of 3300 km, and is the Martian region where the Viking 2 lander touched down and began exploring on September 3, 1976. It is located at the antipode of Argyre Planitia, centered at...
, , in the northern hemisphere, and in the region of Peneus
Peneus
In Greek mythology, Peneus was a Thessalian river god, one of the three thousand Rivers , a child of Oceanus and Tethys. The nymph Creusa bore him one son, Hypseus, who was King of the Lapiths, and three daughters, Menippe , Daphne, and Stilbe. He also had a son Atrax with Bura, and Andreus with...
and Amphitrites Patera in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in insolation
Insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...
. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation (direct transition of a material from the solid to the gas phase with no intermediate liquid stage). This process may still be happening at present. In Utopia Planitia, a series of curvilinear ridges parallel to the scarp are etched on the floor of large scalloped depressions, possibly representing different stages of scarp erosion. Sometimes the surface around scalloped terrain or scalloped topography displays "patterned ground
Patterned ground
Patterned ground is a term used to describe the distinct, and often symmetrical geometric shapes formed by ground material in periglacial regions...
", characterized by a regular pattern of polygonal fractures. These patterns indicate that the surface has undergone stress, perhaps caused by subsidence, desiccation, or thermal contraction. Such patterns are common in periglacial
Periglacial
Periglacial is an adjective originally referring to places in the edges of glacial areas, but it has later been widely used in geomorphology to describe any place where geomorphic processes related to freezing of water occur...
areas on Earth. Scalloped terrains in Utopia Planitia display polygonal features of different sizes: small (abut 5–10 m across) on the scarp, and larger (30–50 m across) on the surrounding terrains. These scale differences may indicate local difference in ground ice concentrations.