This image of phyllosilicates and olivine in the Nili Fossae region of
Mars was taken by the Compact Reconnaissance Imaging Spectrometer for Mars
(CRISM) at 0714UTC (3:14 a.m. EDT) on October 3, 2006 near 20.5 degrees
north latitude, 78.5 degrees east longitude. The image was taken in 544
colors covering 0.36-3.92 micrometers, and shows features as small as 18
meters (60 feet) across.
Nili Fossae is a group of long, narrow depressions comprised of a series
of grabens or down-dropped blocks of crust surrounded by faults. It lies
to the northeast of Syrtis Major (a low and broad shield volcano) and to
the northwest of an impact basin, Isidis Planitia. Nili Fossae stretches
some 667 kilometers (415 miles) toward Utopia Planitia, and has been
partially filled by sediments and volcanic lavas.
The top panel in the montage above shows the location of the CRISM image
on a mosaic taken by the Mars Odyssey spacecraft’s Thermal Emission
Imaging System (THEMIS). The CRISM data covers relatively flat terrain
that holds several small craters.
The lower left image, in infrared false color, reveals craters that hold a
ruddy-brown material on their floors. This material appears to form
pyramid-shaped wedges within the craters, all seemingly “pointing” toward
the northeast which suggests they may be wind deposits. Similar
ruddy-brown material is exposed on the hill at the southwestern corner of
the image, probably a remnant segment of the rim of a very ancient, highly
eroded crater.
The High-Resolution Imaging Science Experiment (HiRISE), which is also
onboard the Mars Reconnaissance Orbiter, has imaged similar regions
elsewhere in Nili Fossae. When combined with CRISM data, the images
revealed the sand dunes to be olivine-rich and commonly lying atop clay
deposits (Clay at Nili Fossae).
The lower right image expands our understanding of the composition of this
area. CRISM data reveal olivine (an iron-magnesium containing igneous
mineral) in blue. The olivine makes up the material on the hill as well as
the crater floors that appears ruddy-brown in the false color image. Other
lower hills, appearing non-descript gray in false color, consist of
ferromagnesian phyllosilicates (red/pink). Both the olivine and the
phyllosilicates, a category of mineral that includes clays, were buried by
material that appears black in the lower right image, probably basaltic
lava rocks. The burial of the olivine-rich hill and the phyllosilicates
indicates that both formed early in Mars' history, before the lava. Later,
small craters formed on the lavas penetrating them and exposing the
underlying olivine, which has been eroded by winds and formed into sand
dunes.
CRISM is one of six science instruments on NASA's Mars Reconnaissance
Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory,
Laurel, Md., the CRISM team includes expertise from universities,
government agencies and small businesses in the United States and abroad.
NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology in Pasadena, manages the Mars Reconnaissance Orbiter and the
Mars Science Laboratory for NASA's Science Mission Directorate,
Washington. Lockheed Martin Space Systems, Denver, built the orbiter.