Cassini observations of the thermal plasma in the vicinity of Saturn's main rings and the F and G rings

The ion mass spectrometer on Cassini detected enhanced ion flux near Saturn's main rings that is consistent with the presence of atomic and molecular oxygen ions in the thermal plasma. The ring "atmosphere'' and "ionosphere'' are likely produced by UV photosputtering of the icy rings and subsequent photoionization of O-2. The identification of the O+ and O-2(+) ions is made using time-of-flight analysis and densities and temperatures are derived from the ion counting data. The ion temperatures over the main rings are a minimum near synchronous orbit and increase with radial distance from Saturn as expected from ion pick up in Saturn's magnetic field. The O-2(+) temperatures provide an estimate of the neutral O-2 temperature over the main rings. The ion mass spectrometer also detected significant O-2(+) outside of the main rings, near the F ring. It is concluded that between the F and G rings, the heavy ion population most likely consists of an admixture of O-2(+) and water group ions O+, OH+, and H2O+

Cassini in situ observations of long duration magnetic reconnection in Saturn’s magnetotail

Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy1, 2, 3, 4. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field5, 6. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn’s magnetotail. The data also show evidence of magnetic reconnection over a period of 19?h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn6. This counters the view of reconnection as a transient method of internal plasma loss at Saturn5, 7. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies

Solar Coronal Plumes

Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features