NASA's Mars Reconnaissance Orbiter (MRO) has helped capture images of the largest fresh meteor-impact crater ever firmly documented.
The crater spans half the length of a football field and first appeared in March 2012.
The impact that created it likely was preceded by an explosion in the Martian sky caused by intense friction between an incoming asteroid and the planet's atmosphere.
This series of events can be likened to the meteor blast that shattered windows in Chelyabinsk, Russia, last year.
The air burst and ground impact darkened an area of the Martian surface about 5 miles (8 kilometers) across.
The darkened spot appears in images taken by the orbiter's weather-monitoring camera, the Mars Color Imager (MARCI).
Since the orbiter began its systematic observation of Mars in 2006, scientist Bruce Cantor has examined MARCI's daily global coverage, looking for evidence of dust storms and other observable weather events in the images. Cantor is this camera's deputy principal investigator at Malin Space Science Systems, the San Diego company that built and operates MARCI and the orbiter's telescopic Context Camera (CTX).
About two months ago, Cantor noticed an inconspicuous dark dot near the equator in one of the images.
He began examining earlier images, skipping back a month or more at a time. The images revealed that the dark spot was present a year ago, but not five years ago. He homed in further, checking images from about 40 different dates, and pinned down the date the impact event occurred; the spot was not there up through March 27, 2012, and then appeared before the daily imaging on March 28, 2012.
Once the dark spot was verified as new, it was targeted last month by CTX and the orbiter's sharpest-sighted camera, the High Resolution Imaging Science Experiment (HiRISE).
Of the approximately 400 fresh crater-causing impacts on Mars that have been documented with before-and-after images, this is the only one discovered using a MARCI image, rather than an image from a higher-resolution camera.
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