The Influence of Mercury's Magnetosphere on Its Outermost Atmosphere

Trustees Of Boston University, Boston

Investigators

Abstract

Many different processes can free atoms from the surface of the planet Mercury. Most atoms then fall back to Mercury's surface. However, some atoms having higher energies can be picked up and pushed by the sun's radiation, extending Mercury's thin atmosphere farther away from the sun. During Mercury's orbit around the sun, the contributions of all of these processes change at different times. Monitoring the signals from emissions of sodium atoms is an excellent way to trace these processes as they occur during Mercury's orbit. The investigators will build an instrument that can see Mercury's surface and its thin atmosphere at the same time, so that they can measure and model sodium's activity in order to understand Mercury's surface/atmosphere processes. This instrument will be installed on a Japanese telescope located in Hawaii. This project will involve a new collaboration between Japanese and United States astronomers, fostering international co-operation that benefits the U.S. The results of this work will be included in university astronomy classes, benefiting student education. Atoms can be liberated from the surface of the planet Mercury by many processes, including photon-stimulated desorption, thermal evaporation, ion sputtering and meteoroid vaporization. Most of these atoms follow a ballistic trajectory, and return to the planet's surface. However, those atoms released with higher energies can be accelerated by solar radiation pressure, creating a coma-like extension of Mercury's exosphere. The relative contributions of these mechanisms to the exosphere are disputed, and recent modeling suggests that no single source mechanism dominates during the entire Mercury year. The investigators will build a new instrument for spectral high-definition imaging to conduct regular, ground-based observations of sodium on Mercury and in its exosphere. Sodium is an excellent tracer of the morphology and dynamics present in Mercury's exosphere system. By producing near-simultaneous spectral images of the sodium brightness enhancements above Mercury's surface and the anti-sunward variations in exospheric sodium, the variability of both sources can be tracked. The observations will then be comprehensively modeled. This investigation will strengthen international collaboration between the Japanese Tohaku University and Boston University through joint observations at the Tohuku 60 cm (24")Telescope on Haleakala, Hawaii. The results from the research will be incorporated into university classes.