BepiColombo—Comprehensive exploration of Mercury: Mission overview and science goals

Observations of radar speckle patterns tied to the rotation of Mercury establish that the planet occupies a Cassini state with obliquity of 2.11 ± 0.1 arc minutes. The measurements show that the planet exhibits librations in longitude that are forced at the 88-day orbital period, as predicted by theory. The large amplitude of the oscillations, 35.8 ± 2 arc seconds, together with the Mariner 10 determination of the gravitational harmonic coefficient C22, indicates that the mantle of Mercury is decoupled from a core that is at least partially molten.

Large Longitude Libration of Mercury Reveals a Molten Core

[1] We present the analysis of 205 spatially resolved measurements of the surface composition of Mercury from MESSENGER’s X-Ray Spectrometer. The surface footprints of these measurements are categorized according to geological terrain. Northern smooth plains deposits and the plains interior to the Caloris basin differ compositionally from older terrain on Mercury. The older terrain generally has higher Mg/Si, S/Si, and Ca/Si ratios, and a lower Al/Si ratio than the smooth plains. Mercury’s surface mineralogy is likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, and lesser amounts of Ca, Mg, and/or Fe sulfides (e.g., oldhamite). The compositional difference between the volcanic smooth plains and the older terrain reflects different abundances of these minerals and points to the crystallization of the smooth plains from a more chemically evolved magma source. High-degree partial melts of enstatite chondrite material provide a generally good compositional and mineralogical match for much of the surface of Mercury. An exception is Fe, for which the low surface abundance on Mercury is still higher than that of melts from enstatite chondrites and may indicate an exogenous contribution from meteoroid impacts.

/pdf/chemical-heterogeneity-on-mercury-s-surface-revealed-by-the-1zsbrpa5bx.pdf

Chemical heterogeneity on Mercury's surface revealed by the MESSENGER X-Ray Spectrometer

http://www.planetary.brown.edu/pdfs/4118.pdf

The global distribution of pyroclastic deposits on Mercury: the view from MESSENGER flybys 1-3.

http://oro.open.ac.uk/16347/1/Fraser_et_al.pdf

P Thomas

Papers

The mercury imaging X-ray spectrometer (MIXS) on BepiColombo