Series: Astronomy Unit Seminars
Speaker: Dr Ingo Mueller-Wodarg (Imperial College)
Abstract: The ongoing Cassini mission as well as a rich set of Earth based observations have given important constraints to our understanding of how Saturn's upper atmosphere is coupled to its magnetosphere. As for the case of Jupiter, angular momentum is transferred from atmosphere to magnetosphere in order to bring sub-corotating plasma to co-rotation. In exchange, energy is transferred from magnetosphere to atmosphere in the form of precipitating particles and Joule heating. This polar energy source on Saturn is larger by a factor of several tens than solar heating and therefore dominates the upper atmosphere in terms of energetics and dynamics. This talk presents comprehensive calculations of the response of Saturn’s coupled thermosphere-ionosphere to forcing by solar radiation, magnetospheric energetic electron precipitation and high latitude electric fields caused by sub-corotation of magnetospheric plasma. Significant recent additions to the physical processes calculated in our Saturn Thermosphere Ionosphere General Circulation Model (STIM-GCM) include the comprehensive and self-consistent treatment of neutral-ion dynamical coupling and the use of self-consistently calculated rates of plasma production from incident energetic electrons. The project examines how energy and momentum are redistributed in the atmosphere. This work is equally of relevance to our understanding of Jupiter, our next target of observation by the forthcoming JUNO and planned JUICE missions. Finally, understanding the physics of magnetosphere-atmosphere coupling on Gas Giants within our solar system is paramount for understanding similar processes occurring on exoplanets as well.