Max Planck Institute for Solar System Research | 2017 Oct 30
The high energy proton population in the environment of Saturn develops independently of the solar wind -- and thus in a considerably different way from the one on Earth.
[img3="© MPS, Image of Saturn: NASA/JPL/SSI"]http://www.mps.mpg.de/5124024/standard_ ... 314403.jpg[/img3][hr][/hr]The radiation belts of Earth and Saturn differ more strongly than previously assumed. In these belts, very energetic particles, such as electrons and protons, move around the planet at high velocities - captured by its magnetic field. In the case of the Earth, the solar wind, a current of charged particles from the Sun varying in strength, controls the intensity of the radiation belt both directly and indirectly. The radiation belts of Saturn, however, develop completely independently of the solar wind and are instead decisively influenced by the gas giant’s moons. These results are published today in the journal Nature Astronomy by a group of researchers from the Max Planck Institute for Solar System Research (MPS) in Germany co-leading the most comprehensive study on the subject to date. Key to the new findings are measurements of the MIMI-LEMMS instrument aboard NASA’s Cassini space probe, which explored the Saturn system for more than 13 years before its dive into the planet on the 15th of September this year.
The activity of the Sun – and with it the strength of the solar wind – follows an eleven-year cycle. Investigating the long term influence of the solar wind on a planet’s radiation belts therefore requires patience – and space missions of a considerable length. "If Cassini’s mission to the Saturn system had ended after four years, as initially planned, we would never have been able to achieve these results," explains Dr. Elias Roussos of the MPS. Fortunately, the mission was extended several times. The Magnetospheric Imaging Instrument (MIMI) with its high energy particle detector (LEMMS) on board Cassini was therefore able to record the distribution of charged particles in the vicinity of Saturn over a period of time that includes a complete solar cycle. "Such extensive in-situ data on the radiation belts of a planet are otherwise only available for Earth," says MPS researcher Dr. Norbert Krupp, who heads the MIMI-LEMMS team. ...
The Evolution of Saturn’s Radiation Belts Modulated by Changes in Radial Diffusion - P. Kollmann et al
- Nature Astronomy (online 30 Oct 2017 DOI: 10.1038/s41550-017-0287-x