About Saturn & Its Moons
Magnetosphere - Why Study Magnetospheres?
Saturn's magnetosphere is formed by its magnetic field. The structure and strength of the field at different locations within the magnetosphere can tell us about Saturn's interior structure and reveal unseen details about how the planet interacts with the solar wind – the flow of electrically charged particles (electrons and ions) blown outward by the sun – which fills interplanetary space. A planet's magnetosphere forms a sort of shield against the solar wind, and its particles respond to the electric and magnetic forces present in this magnetic bubble.
Magnetic fields themselves are invisible, but we can study them with a diverse set of instruments, like those on Cassini. Cameras can take images of auroras formed by magnetospheric particles slamming into the planet's upper atmosphere. Measuring the flow of charged particles around the spacecraft can hint at how Saturn's rings and moons release material into the magnetosphere, interacting with it and modifying it.
Puzzlingly, the rotation rate Cassini measured was slower than that measured 25 years earlier by the Voyager spacecraft. Since an actual slowing of the giant planet's rotation was highly unlikely, scientists had a mystery on their hands. Cassini data later suggested that material blasted into space by the geologic activity on Enceladus was likely to blame. Apparently Saturn's magnetic field is slowed down as it drags through the ring of particles that litter the orbit of Enceladus.
Cassini also observes lightning-produced radio emissions in order to detect and track monster storms that sometimes punch through Saturn's clouds from below. These radio emissions act as an alert to point Cassini's cameras, as well as telescopes on Earth, toward Saturn to monitor the activity of such powerful storms and learn more about them.
Studying the environment of Saturn's magnetosphere reveals other hidden information, like the fascinating possibility that Rhea might have rings of its own. The ghostly ring features called spokes appear to be closely connected to the magnetic field, so magnetosphere studies are key to understanding how they form.