SULFUR AT MERCURY: ELEMENTAL AT THE POLES, SULFIDES IN REGOLITH



ANN L. SPRAGU E

Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
sprague
fax 520-621-4933



D.M.HUNTEN

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.