This images shows a Compact Reconnaissance Imaging Spectrometer for Mars
(CRISM) full-resolution "targeted image" of the edge of Mars' north polar
cap. The region in the image, Chasma Boreale, is a valley several
kilometers or miles deep that cuts about 400 kilometers (about 250 miles)
into the edge of the cap.
This image was acquired at 0851 UTC (4:51 a.m. EDT) on Oct. 1, 2006, near
84.6 degrees north latitude, 3.6 degrees east longitude. It covers an area
about 13 kilometers (8 miles) long and, at the narrowest point, about 9
kilometers (5.6 miles) wide. At the center of the image the spatial
resolution is as good as 18 meters (60 feet) per pixel. The image was
taken in 544 colors covering wavelengths of 0.36 to 3.92 micrometers. Two
renderings of the data are shown here, both draped over topography without
vertical exaggeration, and then viewed from a perspective diagonally above
the site. The top view is an approximately true-color representation. The
bottom view, constructed from infrared wavelengths, shows strength of the
spectral signature of ice. Brighter areas are rich in ice, and dark areas
have little ice.
The polar cap has long been recognized to contain layers composed of dust
and ice, and hence has been named the polar layered deposit. This sits
atop an underlying "basal unit." The upper part of the basal unit is dark
at visible wavelengths and steeply sloped, whereas the lower part of the
basal unit is brighter, redder, and layered like the polar layered
deposits. The chasma floor is cratered, and in the foreground it is
covered by dunes that are outliers of a north polar sand sea that
surrounds the polar cap. The polar layered deposits and the basal unit
form a steeply sloping scarp about 1.1 kilometers (0.7 miles) high.
CRISM's image of this region shows a number of previously unrecognized
characteristics of the polar layered deposits and the basal unit. First,
the ice-rich polar layered deposits exhibit coherent banding both at
visible and infrared wavelengths. This banding shows a history of
differences in the abundance of dust that accumulated in polar ice,
differences in ice grain size, or both. Second, both parts of the basal
unit are depleted in ice, except for triangle-shaped regions on the side
of the scarp. Third, the spectral properties of the brighter, layered
lower basal unit resemble those of the polar layered deposits. In
contrast, the upper basal unit is distinct from both of them. Finally,
spectral properties of the foreground dunes closely resemble those of the
darkest layers within the upper basal unit, and may be debris from it.
CRISM is one of six science instruments on NASA's Mars Reconnaissance
Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory,
the CRISM team includes expertise from universities, government agencies
and small businesses in the United States and abroad.
CRISM's mission: Find the spectral fingerprints of aqueous and
hydrothermal deposits and map the geology, composition and stratigraphy
of surface features. The instrument will also watch the seasonal
variations in Martian dust and ice aerosols, and water content in surface
materials -- leading to new understanding of the climate.
NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology, Pasadena, manages the Mars Reconnaissance Orbiter mission
for the NASA Science Mission Directorate. Lockheed Martin Space Systems,
Denver, is the prime contractor and built the spacecraft.
