Mercury’s enigmatic origin: results from the MESSENGER mission
IPGP - Îlot Cuvier
Séminaires généraux de l’IPGP
Denton S. Ebel
American Museum of Natural History
The MESSENGER mission has clarified planet Mercury’s anomalous density, reduced mantle, and very low albedo. Mercury is not depleted in volatile elements relative to the other terrestrial planets. Mercury’s large core/mantle ratio has been hypothesized to result either from gradual, orderly processes particular to the innermost protoplanetary disk, or from chaotic processes such as a mantle-stripping impact. Substantial reaccretion of silicate material is highly likely for a large impact on proto-Mercury. Collisional simulations can predict Mercury’s high core/mantle ratio, but not its extremely reduced chemistry or its low albedo. Undifferentiated meteorites exist that formed by ‘orderly’ nebular processes and that match the redox state and volatile abundance of Mercury’s silicate fraction. Equilibrium condensation in a vapor enriched in C-rich interplanetary dust can produce both FeO-free silicates and highly reduced minerals. Mechanisms for non-stochastic dynamical metal-silicate fractionation in the innermost disk have been proposed. While a stochastic, chaotic process such as a giant impact cannot be entirely ruled out based on MESSENGER data, it cannot explain Mercury’s full combination of chemical anomalies. In contrast, Mercury may represent a planetary embryo, recording extreme but orderly chemical and dynamical processes in the innermost solar nebula.