THE DISTRIBUTION OF CRYSTALLINE HEMATITE ON MARS FROM THE THERMAL EMISSION
SPECTROMETER: EVIDENCE FOR LIQUID WATER. P.R.Christensen
One of the primary objectives of the Thermal
Emission Spectrometer (TES) instrument on the
Mars Global Surveyor (MGS) spacecraft is to
determine and map the mineralogic composition of
the Martian surface. Of particular interest is the
search for minerals formed through interaction with
water, either by low-temperature precipitation or
weathering, or by hydrothermal mineralization.
Over 50 x10
from the MGS mapping orbit. These spectra
observed from orbit are a complex combination of
surface and atmospheric emitted and transmitted
energy. The spectral features resulting from
atmospheric CO2, dust, and water ice have been
removed using a radiative transfer model [1, 2].
Using these atmospherically-corrected spectra we
have identified two major accumulations of
crystalline hematite (α-Fe2O3) . Crystalline
hematite is uniquely identified by the presence of
fundamental vibrational absorption features centered
near 300, 450, and >525 cm
silicate fundamentals in the 1000 cm
depth and shape of the hematite fundamental bands
show that the hematite is crystalline and relatively
coarse grained (>5-10 µm). Diameters up to and
greater than 100s of micrometers are permitted
within the instrumental noise and natural variability
of hematite spectra. The spectrally-derived areal
abundance of hematite varies with particle size from
~10% (>30 µm diameter) to 40-60% (10 µm
diameter). Crystalline hematite has been previously
reported using visible/near-IR observations , and
nanophase hematite is widely thought to be an
important component of the materials that give Mars
its red color [5-8]. The hematite in Sinus Meridiani
is distinct, however, from the fine-grained (diameter
<5-10 µm), red, crystalline hematite considered, on
the basis of visible, near-IR data, to be a minor
spectral component in Martian bright regions.
Crystalline hematite has been mapped over an
area in Sinus Meridiani approximately 500 km in
longitude extending approximately 200 km in
latitude . The extent of this deposit very closely
matches the geomorphic boundary of a smooth,
layered, friable unit that is interpreted to be sedi-
Christensen, Separation of atmospheric and surface
1, M. Malin
3, D. Morris
5, J. Band-
1, M. Lane
2U.S.Geological Survey, Denver, CO;
5Johnson Space Center, TX;
1, K. Edgett
1Dept. of Geology, Campus Box 871404, Arizona State University, Tempe, AZ 85287-
3Malin Space Science Systems, CA;
6Ames Research Center, Moffet Field, CA,
4U. S. Geological Survey, Flag-
7Goddard Space Flight Center,
6 spectra have been observed to date
-1, and by the absence of
-1 region. The
mentary in origin [3, 9]. This material may be the
uppermost surface in the region, indicating that it
might be a later-stage sedimentary unit, or alterna-
tively a layered portion of the heavily cratered
A second accumulation of hematite approxi-
mately 60 x 60 km in size is observed in Aram
Chaos (2° N, 21° W). This site is also associated
with layered materials and a water-rich environ-
We consider five possible mechanisms for the
formation of coarse-grained, crystalline hematite.
These processes fall into two classes depending on
whether they require a significant amount of near-
surface water: (1) chemical precipitation that
includes origin by (a) precipitation from standing,
oxygenated, Fe-rich water (oxide iron formations),
(b) precipitation from Fe-rich hydrothermal fluids,
(c) low temperature dissolution and precipitation
through mobile ground water leaching, and (d)
formation of surface coatings; and (2) thermal
oxidation of magnetite-rich lavas . We favor
chemical precipitation models involving precipita-
tion from Fe-rich water based on the probable
association with sedimentary materials, large
geographic size, distance from regional heat sources,
and lack of evidence for extensive groundwater
processes elsewhere on Mars.
The TES results provide mineralogic evidence
for probable large-scale water interactions. The
Sinus Meridiani region may be an ideal candidate
for future landed missions searching for biotic and
pre-biotic environments, and the physical character-
istics of this site satisfy the engineering require-
ments for the missions currently being considered.
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Lunar and Planetary Science XXXI
HEMATITE ON MARS: P.Christensen, M. Malin, D. Morris, J. Bandfield, M. Lane, K. Edgett Download full-text
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