Rare Polar Martian impact craters revealed

Washington, Oct 16 : Scientists have used the HiRise (High Resolution Imaging Science Experiment) camera onboard NASA's Mars Reconnaissance Orbiter to reveal rare Polar Martian impact craters.

The north polar layered deposits are stacked up to several kilometers thick and represent one of the largest surface reservoirs of Martian water that interacts with the planet's atmosphere, according to LPL's Shane Byrne.

Scientists believe the deposits record orbitally driven climate changes and study them to learn how Mars climate evolved.

The new HiRISE image shows an exposed 500-meter thick section (1,640 feet) of this layering, and also a 40-meter high (130-foot) conical mound sticking out of the slope.

"The mound may be the remnant of a buried impact crater, which is now being exhumed," Byrne said.

Impact craters would have been buried by ice as the layered deposits accumulated, with layers wrapping around the crater. Almost none exist on the surface of this terrain.

"But in this rare case, erosion formed a trough that uncovered one of these structures. For reasons that are poorly understood right now, the ice beneath the site of the crater is more resistant to this erosion, so that as this trough formed, ice beneath the old impact site remained, forming this isolated hill," said Byrne.

Viewing the HiRISE image at full resolution shows that the mound is made up of polygonal blocks as big as 10 meters, or 33 feet, across.

The blocks are covered with reddish dust, but otherwise resemble ice-rich blocks seen in other images of the north polar layered deposits.

The seven new HiRISE images include another image of an impact crater where such features are rarely seen on the north polar cap.

HiRISE turned up a small crater, only about 115 meters, or 125 yards, in diameter on the surface of Planum Boreum, popularly known as the north polar cap.

The dearth of craters has led scientists to suggest that either the north polar cap is only about 100,000 years old or that crater impacts into the ice disappear as the ice relaxes, just as imperfections disappear as old window glass relaxes.

HiRISE has returned more than 8,200 gigapixel-size images of Mars' surface since the start of its science mission in November 2006.

The HiRISE team so far has released a total of about 27 terabytes of data, more than all previous deep space missions combined.

ANI