This false color image covers the western half of the central peak of Toro Crater, a 42 kilometer diameter crater in Syrtis Major.

The subimage shows a close-up of one of the features that make Toro Crater a great target for HiRISE images: colorful patches of megabreccia. Breccia is a mixture of chunks of rock (clasts) that have been broken by an energetic geologic event, such as a landslide or crater-forming impact, that are then cemented together in a finer grained material. Megabreccia features very large clasts that are big enough for HiRISE to see on the surface - some even larger than 30 feet across. In this 200 meter (about 1/8 of a mile) diameter exposure of megabreccia, clasts of various colors (indicating different kinds of rocks) and sizes have been exposed in the uplifted central peak of Toro Crater.

Scientists think that megabreccia may have formed early in Mars' history during a period of frequent impact crater formation. These early rocks were then covered by younger rock layers. HiRISE frequently targets the central peaks of craters, because these features tend to bring up rocks like these megabreccia that are usually buried under the surface.

So far, HiRISE has found megabreccia in more than a hundred places on Mars. In many of these locations, CRISM has identified clays in the material cementing the clasts together, providing yet another motivation for the study of megabreccia.

HiRISE first imaged Toro Crater (in PSP_005842_1970) because CRISM detected hydrated minerals, like clays, on the floor. The instruments of MRO often observe the same areas of Mars simultaneously through a process known as "ride-alongs." That earlier image was so interesting that HiRISE has since acquired a number of images over the crater (PSP_006910_1975, PSP_007266_1970,ESP_011538_1970)
Written by: Nicole Baugh

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.