Gullies, Arcuate Ridges, and Scalloped Terrain in Acidalia Planitia
Gullies, Arcuate Ridges, and Scalloped Terrain in Acidalia Planitia
PSP_006690_2280  Science Theme: Glacial/Periglacial Processes
This image covers the eastern part of an unnamed crater located in the northern lowlands, showing features such as gullies, arcuate (bow-like) ridges, and scalloped terrain, that may indicate the presence of ice-rich materials near the surface.

As the CTX context subimage shows, the crater has gullies in its northern half (equator-facing slopes); no gullies are apparent in the southern half (pole-facing slopes). This observation is in agreement with theories proposing that some Martian gullies could form by melting of an ice rich-mantle deposited under different climatic conditions. Such ice-rich materials would be especially unstable in equator-facing slopes, where they would be exposed to maximum insolation (solar illumination).

The HiRISE image also shows arcuate ridges where the crater’s slopes meet the floor. These ridges are 10-to-30 meter (30-to-100 feet) wide and can be followed for hundreds of meters (yards). They are similar to terrestrial features produced by mass wasting of ice-rich materials.

This HiRISE subimage (358 x 266 m or 392 x 291 yards) shows incipient scalloped terrain in the southern slopes of the crater. Scalloped terrain—depressions with scalloped edges and polygonal fractures—has been interpreted as a sign of surface caving, perhaps due to sublimation (evaporation) of underlying ice.

Written by: Sara Martinez-Alonso  (13 February 2008)
Acquisition date
30 December 2007

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
304.8 km (189.4 miles)

Original image scale range
30.6 cm/pixel (with 1 x 1 binning) so objects ~92 cm across are resolved

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25 cm/pixel and North is up

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Solar incidence angle
53°, with the Sun about 37° above the horizon

Solar longitude
10.4°, Northern Spring

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North azimuth:  96°
Sub-solar azimuth:  321.3°
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NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.