Spectra collected by the Compact Reconnaissance Imaging Spectrometer for
Mars (CRISM) indicate the presence of three distinct minerals. The graphed
information comes from an observation of terrain in the Nili Fossae area
of northern Mars. CRISM is one of six science instruments on NASA's Mars
Reconnaissance Orbiter.
Iron-magnesium smectite clay is formed through alteration of rocks by
liquid water and is characterized by distinctive absorptions at 1.4, 1.9,
and 2.3 micrometers due to water (H2O) and OH in the atomic structure of
the mineral. Olivine is an iron magnesium silicate and primary igneous
mineral, and water is not in its structure. Its spectrum is characterized
by a strong and broad absorption at 1.0 micrometer due to ferrous iron
(Fe2+). Carbonate is an alteration mineral identified by the distinctive
paired absorptions at 2.3 and 2.5 micrometers. The precise band positions
at 2.31 and 2.51 micrometers identify the carbonate at this location as
magnesium carbonate. The broad 1.0 micrometer band indicates some small
amount of ferrous iron is also present and the feature at 1.9 micrometers
indicates the presence of water. CRISM researchers believe the magnesium
carbonate found in the Nili Fossae region formed from alteration of
olivine by water.
The data come from a CRISM image catalogued as FRT00003E12. The spectra
shown here are five-pixel-by-five-pixel averages of CRISM L-detector
spectra taken from three different areas within the image that have then
been ratioed to a five-pixel-by-five-pixel common denominator spectrum
taken from a spectrally unremarkable area with no distinctive mineralogic
signatures. This technique highlights the spectral contrasts between
regions due to their unique mineralogy. The spectral wavelengths near 2.0
micrometers are affected by atmospheric absorptions and have been removed
for clarity.
NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the
NASA Science Mission Directorate, Washington. Lockheed Martin Space
Systems, Denver, is the prime contractor for the project and built the
spacecraft. The Johns Hopkins University Applied Physics Laboratory led
the effort to build the CRISM instrument and operates CRISM in
coordination with an international team of researchers from universities,
government and the private sector.
