NASA discovers huge crater on Mars

A huge new crater on the surface of Mars - spanning half the length of a football field - has been discovered by a NASA spacecraft orbiting the Red Planet.
Researchers found the largest fresh meteor-impact crater ever firmly documented with images captured by NASA's Mars Reconnaissance Orbiter (MRO).
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 8 kilometres across.

About two months ago, scientist Bruce Cantor noticed an inconspicuous dark dot near the equator in one of the images.

"It wasn't what I was looking for. I was doing my usual weather monitoring and something caught my eye. It looked usual, with rays emanating from a central spot," Cantor said.
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.

"The biggest crater is unusual, quite shallow compared to other fresh craters we have observed," said HiRISE Principal Investigator Alfred McEwen of the University of Arizona.
The largest crater is slightly elongated and spans 159 by 143 feet.
McEwen estimates the impact object measured about 3 to 5 meters long, which is less than a third the estimated length of the asteroid that hit Earth's atmosphere near Chelyabinsk.