Energetic particles in Saturn's magnetosphere during the Cassini nominal mission (July 2004-July 2008)

摘要

In July 2004 the Cassini spacecraft began its orbital tour in the Saturnian system and performed 74 orbits during the nominal mission (July 2004-July 2008) providing data from nearly all local times at various distances and latitudes relative to the planet. The particles and field instruments onboard the spacecraft were essentially operating continuously offering the possibility to study the global configuration and the dynamics of the second largest magnetosphere in our solar system extensively. One of those instruments aboard Cassini is the Low Energy Magnetospheric Measurement System (LEMMS), one of three particle detectors of the Magnetospheric Imaging Instrument (M1MI). M1M1/ LEMMS measures the intensity, energy spectra and pitch angle distributions of energetic ions (E> 30 keV) and electrons (E > 20 keV) separately. The measured energetic particle distributions together with the measured magnetic field provide a very powerful tool to investigate the Saturnian magnetosphere in those regions covered by the Cassini orbits. This paper will give an overview of the energetic particle measurements of the M1M1/LEMMS sensor in the Saturnian system. In the first part of the paper synoptic maps will be shown where all the data are presented as a function of various trajectory parameters of the spacecraft. Secondly bi-directional electron distributions along the magnetic field direction will be described as a feature in the Saturnian system. Thirdly the particle parameters in the inner magnetosphere with absorption signatures of the various moons are presented. Fourthly it will be shown that the region around about 15R_S seems to be a characteristic region where depletion signatures in energetic particle distributions are very often observed. At the end of this work a 60min intensity periodicity in the MIMI/LEMMS data is discussed.