Polar Layers Near Chasma Boreale

This is an image of the north polar layered deposits (NPLD) near the source
region of Chasma Boreale. Chasma Boreale is the largest re-entrant trough in
the NPLD, with its head region located roughly 300 km from the north pole and
its mouth opening into the northern plains at the perimeter of the NPLD.
Chasma	Boreale is thought to have formed due to outflow of water from
underneath the polar cap, or due to winds blowing off the polar cap, or a
combination of both. Investigation of the currently visible layers around the
source region may tell us if they have been deformed and down-dropped,
perhaps by melting and flow of water beneath, or if they remain undisturbed.
Layers here do not appear as fine as elsewhere in polar trough exposures,
although this may be due to the relatively gently sloping exposure here.
Different layers show very different degrees of roughness and pitting,
although the texture within a layer is quite consistent. One of the layers
even displays a texture of polygons 3-10 m across, normally associated with
periglacial freeze-thaw processes on Earth. Layers of different texture,
brightness, and appearance indicate differing physical properties,
composition, and exposure to surface environmental conditions at time of
emplacement and/or erosion. In this way, polar layers on Mars record a
history of climate conditions as sequences of layers on Earth often do.

Image TRA_000840_2750 was taken by the High Resolution Imaging Science 
Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on
September 30, 2006. The image is centered at 84.7 degrees latitude, 16.1 degrees 
East longitude. The range to the target site was 319 km (199 miles). At this 
distance the image scale is 32 cm/pixel (with 1 x 1 binning) so objects ~96 cm 
across are resolved. The image shown here has been map-projected to 25 cm/pixel 
and north is up. The image was taken at a local Mars time of 3:28 PM and the 
scene is illuminated from the west with a solar incidence angle of 68.1 degrees, 
thus the sun was about 21.9 degrees above the horizon. At a solar longitude of 
114.2 degrees, the season on Mars is Northern Summer / Southern Winter.

Images from the High Resolution Imaging Science Experiment and additional
information about the Mars Reconnaissance Orbiter are available online at: 
http://www.nasa.gov/mro or http://HiRISE.lpl.arizona.edu.

For information about NASA and agency programs on the Web, visit:
http://www.nasa.gov.

JPL, 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 Corporation and is operated by the University of
Arizona.