PSP_002281_2115 shows a secondary crater field. Secondary craters form when material ejected from a larger impact event impacts the Martian surface. One impact event, depending on the size of the impactor, can form hundreds of millions of secondary craters at essentially the same time.

Primary craters (those created directly from an impactor from space) can be the same size as secondary craters, which makes dating surfaces based on the number of accumulated craters difficult to near-impossible. Secondary craters are distinguished from primaries based on their morphologies. They are sometimes irregularly shaped, as seen in this image, because they form at relatively low velocities. The velocity of the impactor determines a crater’s size, shape, and depth, with lower energy impacts forming shallow, less-developed craters and higher energy impacts forming deeper, more regular craters.

Secondary craters often occur in clusters, as seen here, as a piece of ejecta breaks up before hitting the surface. Primary craters form at random locations globally. Secondary clusters are more likely to be found in groups because of their formation mechanism.
Written by: Kelly Kolb

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.