Details

Autor(en) / Beteiligte

• Glass, A. N.
• Raines, J. M.
• Jia, X.
• Sun, W.
• Imber, S.
• Dewey, R. M.
• Slavin, J. A.

Titel

Observations of Mercury's Plasma Sheet Horn: Characterization and Contribution to Proton Precipitation

Ist Teil von

• Journal of geophysical research. Space physics, 2022-12, Vol.127 (12), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2022

Link zum Volltext

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• The Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft was the first spacecraft to orbit the planet Mercury. Previous analysis of MESSENGER data has established that of all the planets in the solar system, Mercury's magnetosphere is the most like Earth's, dominated by the Dungey cycle in its dynamic response of the magnetosphere to solar wind forcing. In this work, we identify and describe for the first time Mercury's northern plasma sheet horn—a Dungey cycle feature key to plasma precipitation. We find three possible geometries for potential horn observation by MESSENGER and describe a case study of each. Two additional case studies are presented with geometries particularly favorable to estimating plasma precipitation within the horns. Estimates of proton precipitation flux are performed, which show precipitation levels on the order of 107 per cm2 per second, on the same order of magnitude as the estimated proton precipitation flux in the dayside cusp despite the higher average energy of the protons in the horn. Potential paths for future study of the horns are discussed. Plain Language Summary The Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft was the first spacecraft to orbit the planet Mercury. Previous analysis of MESSENGER data has established that of all the planets in the solar system, Mercury's magnetosphere is the most like Earth's. In this work, we identify and describe for the first time Mercury's northern plasma sheet horn—a key feature present in Earth's magnetosphere which acts to guide plasma toward the surface. We find that, at Mercury, this plasma precipitates onto the planetary surface through the plasma sheet horn at a rate similar to rates previously observed for plasma precipitation on the planet's dayside. We discuss how the horn is a particularly important region for future study, because the average energy of the particles in the horn is different to particles on the dayside, and because the region of space over which the nightside precipitation happens can vary significantly. Key Points Mercury's northern plasma sheet horn was observed by the Fast Imaging Plasma Spectrometer and magnetometer instruments aboard Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) MESSENGER traversed the plasma sheet horn in three different geometries over the course of its mission at Mercury Proton precipitation rates in the plasma sheet horn are of the same order of magnitude as those in Mercury's dayside cusp