Water content of the Martian soil: Laboratory simulations of reflectance
spectra
Albert S. Yen, Bruce C. Murray, George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91125-2500, U.S.A.
Abstract
Reflectance spectra from the surface of Mars collected by instruments such
as the imaging spectrometer (ISM) onboard the 1988 Soviet Phobos 2 spacecraft
exhibit strong 3 um absorption features that have long been attributed to
hydrated materials on the Martian surface. This interpretation is consistent
with a series of chemical weathering models suggesting an abundance of palagonites,
clays, and other hydrated mineral phases in the Martian fines. Little work,
however, has been done to constrain the actual water content of the Martian
surface materials. New laboratory data presented here show that the ISM spectra
are consistent with up to 4% water by weight and that the deep hydration features
observed in the spacecraft data could be due to less than 0.5% water if the
hydrated phases are present in the form of grain coatings. These results are
consistent with the somewhat uncertain in situ measurements obtained by the
Viking landers which yielded approximately 2 wt% water from samples heated
to 500°C. On the basis of this work, we expect the TEGA instrument on
the Mars '98 lander to find less than 4% adsorbed or bound water in the upper
few centimeters of the Martian soil.
Journal of Geophysical Research 103, 11,125-11,133