Using MESSENGER Data to Model the Thermochemical Evolution of Mercury's Interior

Abstract:

Understanding the evolution of terrestrial planets, such as Mercury, is key to understanding the planetary differences seen today. The MESSENGER mission, launched in 2004, collected data to improve our understanding of the formation, evolution, and space environment of Mercury. MESSENGER indicated the surface was rich in Mg and S (and other moderately volatile and volatile (e.g., C) elements), but Ti and Fe poor, suggesting the surface (and interior) could be dominated by Mg-rich silicate minerals, as well as sulfides. Further, the high S and low Fe contents of the surface volcanics indicate they formed under very reducing conditions. This implies the mantle has a similarly low FeO content, less than 1 wt.%, and a high S content, around 7 wt.%. To understand the thermal evolution of Mercury’s mantle, a focused study will be done on the Northern Volcanic Plains region, which provides insight into the composition of the Mercurian mantle. We will use a thermal model to understand the mantle’s temperature evolution.

Using the mission data described above, in addition to previous experimental data, we provide constraints on the mantle’s thermal evolution. Assuming a homogeneous mantle composition, with the known values of the heat producing elements (K, Th, and U), and the associated liquidi and solidi estimates, we can analyze the melting of the mantle. We will construct a thermochemical model to describe the thermal and melting history of the mantle which generated the Northern Volcanic Plains This model will analyze a range of bulk compositions, volatile content, and oxygen fugacities. Results from this model will be compared to the known age of the Northern Volcanic Plains to create a snapshot of the mantle’s evolution. Comparing the melt composition and melt volume from this model to the observed surface composition, we will determine how the thermochemical evolution of the Northern Volcanic Plains connects with the overall thermal evolution of the planet.