Characteristics of Energetic Electron Events in Mercury’s Magnetosphere at the 10-ms Timescale

Tuesday, 16 December 2014
Ralph L McNutt Jr1, John O Goldsten1, David J Lawrence1, Richard D Starr2, George C Ho1, Patrick N Peplowski1, Brian J Anderson1, Haje Korth1, Stamatios M Krimigis1,3, Robert E Gold1, Sean C Solomon4,5 and Daniel N. Baker6, (1)Johns Hopkins Univ/APL, Laurel, MD, United States, (2)Catholic University of America, Washington, DC, United States, (3)Academy of Athens, Office of Space Research and Technology, Athens, Greece, (4)Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC, United States, (5)Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, United States, (6)University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States
Throughout its orbital mission, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has detected energetic electrons at Mercury. The electrons have been measured by the Energetic Particle Spectrometer (EPS) component of the Energetic Particle and Plasma Spectrometer (EPPS). Fewer but related bursts of hard X-rays measured by the sensors of the Gamma-Ray and Neutron Spectrometer (GRNS) on the MESSENGER spacecraft are identified as bremsstrahlung from these electron events produced within the sensors of these instruments. Following failure of the GRS cryogenic cooler required for measurement of gamma-rays of planetary origin, the GRS anticoincidence shield (ACS) of borated plastic has remained fully functional and able to detect neutrons and energetic electron (EE) events. Intensity, but not energy information, is now routinely obtained at a 10-ms cadence, compared with the 600-ms temporal resolution of the energetic particle detector on Mariner 10. Similar data, but at a slower cadence, also are provided by the scintillators of MESSENGER’s Neutron Spectrometer (NS). The X-Ray Spectrometer (XRS) on MESSENGER makes regular observations of photons produced by the impingement onto its detectors of low-energy (~10 keV) electrons and hence provides the primary measure of this lower-energy suprathermal electron population at Mercury. The accumulating data of the EPS, XRS, GRS ACS, and NS continue to show that these suprathermal electrons are persistent at all longitudes and that a substantial fraction are found in the dawn sector. As Mercury’s orbit continues to evolve as a result of solar gravitational perturbations, this instrument suite will continue to probe the spatial and temporal structure of these events in magnetospheric regions not yet sampled. Combined with the magnetic field model of the planet, these additional measurements will constrain further the sources and energization mechanism of these energetic electrons.