This image shows a typical landscape from the far western part of Utopia Planitia in the Northern lowlands of Mars.

These areas are characterized by a network of polygonal cracks and elongated, scallop-shaped depressions. The cracks are similar to thermal contraction cracks in periglacial and alpine regions on Earth formed by seasonal contraction of the permafrost (permanently frozen ground). In cold regions of Earth, polygonal cracks like this usually indicate ground ice.

The scalloped depressions (or “scallops”) generally have a steep “pole-facing” scarp and a gentle “equator-facing” slope. Scallop formation may be due to the degradation of ice-rich subsurface material by sublimation (process of ice going directly from a solid state to a gas state). On scallop floors, we often see nested series of curvilinear ridges that probably point to earlier locations of the scarp and contribute to the “shell-like” appearance.

Scallops are observed in other areas of the Martian mid-latitudes (40 to 60 degrees) in both northern and southern hemispheres. They probably represent a form of degradation that erodes an ice-rich mantle thought to have been deposited by precipitation during periods of high obliquity (the tilt of the Martian axis of rotation relative to the plane of Mars’ orbit). These features add weight to the evidence that water ice has been a dynamic component of the Martian sub-surface during recent geological ages and they they may slowly be continuing their development at the present time.


Written by: Alexandra Lefort

All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible: Image: NASA/JPL/University of Arizona

For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. 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. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. The image data were processed using the U.S. Geological Survey’s ISIS3 software.