Saturday, March 08, 2008

Holden crater - cup of life?

It may have have only held water for a few thousand years, but evidence gathered by the High Resolution Imaging Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter may well show that life had a chance of finding a foothold in Holden crater. The HiRise camera has spotted a jumble of house-sized rocks, called megabreccia, in the 154-kilometre-wide Holden Crater. They were probably formed in the impact that created the crater, but a spectrometer on MRO, called CRISM has discovered that the rocks are covered by layers of fine sediments and clay. Such material forms through prolonged contact with water. The evidence points to two wet periods in the history of the crater. The first would have lasted several thousands years, then later water from a network of large channels called the Uzboi Vallis system inundated the surrounding landscape. The crater wall held back the water for a time, before it rose high enough to flood the interior. This wet period would have lasted several hundred years, but it was this rapid flood that scattered the megabreccia and exposed clay that had been covered over by sediments from the first lake. Holden crater is one of 6 prime landing sites under consideration for the 2009 Mars Science Laboratory, and this discovery is sure to increase its chances of selection.