Image credit: NASA/JPL-Caltech

Prior to Cassini’s Grand Finale, our knowledge of the vertical distribution of Saturn’s ionospheric electron densities relied upon the remote observations using radio occultation measurements. For the first time in the history of space exploration, Cassini’s instruments were able to take measurements inside Saturn’s ionosphere. As reported in a new Geophysical Research Letters paper, Cassini’s Grand Finale orbits in 2017 spanned five months and carried the spacecraft deep into Saturn’s ionosphere, enabling the Radio and Plasma Wave Science (RPWS) instrument to obtain the first in situ measurements of Saturn’s ionospheric plasma. Modeling of the electron density measurements shows that the ionosphere extends over an altitude range of more than 15,000 kilometers, with the electron density decreasing exponentially with altitude. The high altitude electron density is greater in the northern hemisphere than it is in the southern hemisphere. This is thought to be due to the effects of ring shadows in the south, which reduce the rate of ionization. READ MORE »