These images from the Context Camera (CTX) on NASA's Mars Reconnaissance Orbiter were taken before (left) and after (right) an apparent impact scar appeared in the area in March 2012 and was detected in images from the orbiter's Mars Color Imager (MARCI). Comparing the Jan. 16, 2012, image on the left with the April 6, 2014, image on the right confirms that two adjacent fresh craters appeared during that interval.
Each of these two images covers an area about 1 mile (1.6 kilometers) across. The craters are within the inscribed rectangle of the "after" image. The larger of the two craters is 159 feet (48.5 meters) wide, making it the biggest fresh crater ever clearly confirmed with before-and-after images, on Mars or anywhere else. Follow-up observations with the same orbiter's High Resolution Imaging Science Experiment (HiRISE) camera (see http://mars.nasa.gov/mro/multimedia/images/?ImageID=6257) reveal additional details of the impact site, including the presence of many smaller craters.
Many of the approximately 400 fresh impact craters on Mars that have been confirmed with before-and-after images were first seen as dark scars detected in CTX images and then confirmed to have craters within the scars when follow-up observations were made with the High Resolution Imaging Science Experiment (HiRISE) camera. This impact is the only one, so far, big enough for the scar to be first detected in MARCI images (see http://mars.nasa.gov/mro/multimedia/images/?ImageID=6256), with follow-up confirmation of a crater by CTX.
CTX is one of six instruments on NASA's Mars Reconnaissance Orbiter. The camera was built by and is operated by Malin Space Science Systems, San Diego. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.