Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
sprague
fax 520-621-4933
Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
dhunten
K. LODDERS
Washington University, St. Louis, MO 63130
ABSTRACT
(ICARUS 118, 211-215, 1995)
We propose that the bright radar spots seen at high latitudes
on Mercury are a result of volume scattering from elemental sulfur.
We also suggest that Mercury's regolith contains sulfides, thus
explaining the high index of refraction derived from its reflected
phase function. We believe that a reducing environment existed
at formation, partitioning sulfur into the core. Early volcanism
and fumarole activity deposited sulfide minerals following (or
concomitant to) the period of crustal solidification when
thick beds of plagioclase were formed. Meteoritic volatilization
and degassing serve as liberation mechanisms for elemental sulfur
to get into the atmosphere and we estimate a column abundance of SI of
~8x10^11 atmos/cm^-2.
An ideal way to test this theory is to search for resonant emissions in the
SI multiplet centered at 1614 Angstroms. The atmospheric sulfur interacts with
the surface and migrates to permanently shadowed regions and form deposits
seen from Earth in radar backscatter. We estimate that with the expected
number density of n = 3 x 10^5 SI atoms cm^-3, the deposition
rate is 35 m per billion years of daylight.
Correction in ICARUS 123, 247, 1996.