This observation is centered within Antoniadi Crater. This crater, even prior to the MRO mission, was identified as a likely ancient lake (now dry) that was supplied by both surface water and ground water.

The image provides further tantalizing evidence of a water-rich past. Most of the flat parts of the image have a polygonal texture, which commonly forms when mud dries. In the center of the image are branched (“dendritic”) features that connect southward to a larger trunk-shaped landform; the branches resemble stream channels on Earth. Unlike active channels with water, these features are “inverted,” or elevated above the surrounding terrain. Again, in analogy with such features seen on our planet, these probably formed when materials deposited by the streams, such as coarse gravel, or chemical cementation after removal of the water, caused the channel bottoms to become resistant. Over time, natural erosion from wind and other processes left the inverted channels elevated above the surrounding terrain.

The branched features are probably remnants of small tributary streams that fed the larger trunk-shaped stream. It appears that the inverted streams lie on top of, and are therefore younger, than the polygons. This area may have first had a lake that later dried to form the polygons, followed by episodes of stream flow and erosion.
Written by: Nathan Bridges

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.