Mercury’s Surface Composition and Character as Measured by Ground-Based Observations

Abstract

Mercury's surface is thought to be covered with highly space-weathered silicate material. The regolith is composed of material accumulated during the time of planetary formation, and subsequently from comets, meteorites, and the Sun. Ground-based observations indicate a heterogeneous surface composition with SiO 2 content ranging from 39 to 57 wt%. Visible and near-infrared spectra, multi-spectral imaging, and modeling indicate expanses A. Sprague ( ) Lunar and A. Sprague et al.of feldspathic, well-comminuted surface with some smooth regions that are likely to be magmatic in origin with many widely distributed crystalline impact ejecta rays and blocky deposits. Pyroxene spectral signatures have been recorded at four locations. Although highly space weathered, there is little evidence for the conversion of FeO to nanophase metallic iron particles (npFe 0 ), or "iron blebs," as at the Moon. Near-and mid-infrared spectroscopy indicate clino-and ortho-pyroxene are present at different locations. There is some evidence for no-or low-iron alkali basalts and feldspathoids. All evidence, including microwave studies, point to a low iron and low titanium surface. There may be a link between the surface and the exosphere that may be diagnostic of the true crustal composition of Mercury. A structural global dichotomy exists with a huge basin on the side not imaged by Mariner 10. This paper briefly describes the implications for this dichotomy on the magnetic field and the 3 : 2 spin : orbit coupling. All other points made above are detailed here with an account of the observations, the analysis of the observations, and theoretical modeling, where appropriate, that supports the stated conclusions.

Statistical analysis of the flux of micrometeoroids at Mercury from both cometary and asteroidal components

“…Also, Sun-grazing comets should be further investigated as a possible source (Sprague et al 2007). With this work, we intend to distinguish between the potential fluxes due to cometary and asteroidal sources to better understand the contribution of the two components.…”

Accommodation of lithospheric shortening on Mercury from altimetric profiles of ridges and lobate scarps measured during MESSENGER flybys 1 and 2

“…Reflectance and emission spectra measured from Earth-based telescopes (Vilas, 1988;Sprague et al, 1994Sprague et al, , 1997Sprague et al, , 2007Sprague et al, , 2009) and the geological analysis of color and high-resolution monochrome images obtained from MESSENGER's flybys (Head et al, 2008(Head et al, , 2009aRobinson et al, 2008;Denevi et al, 2009) indicate that a considerable fraction of Mercury's crust had a volcanic origin. A basaltic or diabase composition, with relatively low FeO and substantial plagioclase content, is plausible for the volcanic material, and by extension olivine is likely a major mineral in Mercury's upper mantle (BVSP, 1981).…”

Identification and measurement of neutron-absorbing elements on Mercury’s surface

“…Specifically, there has been much debate about the Fe content of Mercury's surface materials (e.g., Sprague et al, 2007;Boynton et al, 2007). For example, 1-lm absorption bands resulting from Fe 2+ in silicates are either absent or very weak in reflectance spectra of Mercury at visible to near-infrared wavelengths.…”