Chasma Boreale
Highlighted Portion of HiRISE Image TRA_000845_2645This sub-image shows the basal layers of North Polar Layered deposits. The floor of Chasma Boreale is at the bottom of the image. Pixel scale is 64 cm/pixel (bin 2), and the scene is 568 m wide. This remarkable image is located at the head of a large chasm, named Chasma Boreale, which cuts through the north polar layered deposits (NPLD). The NPLD are an ice-rich layered deposit about 3000 meters (9800 feet) thick and 1000 kilometers (1600 miles) across, much like the Greenland ice-sheet on Earth. The head of Chasma Boreale ends in a steep icy cliff over 1000 meters (3300 feet) high which has both light- and dark-toned layers, shown in the right of the full HiRISE image. The internal layers of the ice-sheet are visible in the cliff walls. The dark-toned flat area in the center and left of the image is the floor of this chasm which contains many craters. Scientists think Chasma Boreale was formed by a catastrophic flood which began under the ice-sheet and was later widened by eolian (wind) erosion. However, the large number of craters on the chasm's floor implies that the floor is much older than the ice sheet. These craters should have been removed by the suggested flood; their presence has caused some Mars' researchers to instead speculate that no large flood occurred and that Chasma Boreale was not covered with very much ice In addition to layered ice, there is also some material within the NPLD that appears to be composed of sand. The dark material near the base of the cliff wall is thought to be aprons of debris being eroded from sand-rich layers. Zooming in on this dark material with HiRISE allows us to see ripples, which are diagnostic of moving sand. Bright spots of material are visible on the cliff-wall which were not present in previous years. These are mostly likely patches of water frost. Each year layers of carbon dioxide and water frost coat this terrain before being removed during the summer. The water frost lasts longer and patches which are shaded by nearby steep topography (such as this one) can even persist into the late summer. An unexpected surprise, not visible with previous camera resolutions, is the fragmentation of the exposed surfaces of these icy layers into polygonal blocks. These blocks appear to be breaking away from the layer margins and forming boulder-sized debris which then rolls down slope (a process called mass-wasting). These boulders are likely to be large blocks of dusty water ice; once separated from the main ice-sheet they can be eroded away by sunlight. More boulder-sized objects are visible out in the floor of the chasm. Polygons are also visible throughout the chasm floor, indicating that water-ice is just below the surface.
Image TRA_000845_2645 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on October 1, 2006. The complete image is centered at 84.6 degrees latitude, 3.4 degrees East longitude. The range to the target site was 318.5 km (199.1 miles). At this distance the image scale is 63.7 cm/pixel (with 2 x 2 binning) so objects ~191 cm across are resolved. The image shown here [below] has been map-projected to 50 cm/pixel. The image was taken at a local Mars time of 1:34 PM and the scene is illuminated from the west with a solar incidence angle of 62 degrees, thus the sun was about 28 degrees above the horizon. At a solar longitude of 114.3 degrees, the season on Mars is Northern Summer.
HiRISE Image TRA_000845_2645
Images from the High Resolution Imaging Science Experiment and additional information about the Mars Reconnaissance Orbiter are available online at:
http://hirise.lpl.arizona.edu/
or
For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.
