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About Saturn & Its Moons

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Magnetosphere - Why Study Magnetospheres?

Artist Concept of Particle Population in Saturn's Magnetosphere
The solar wind flows around Saturn’s force field – the magnetosphere
Studying Saturn's magnetosphere yields important information about the planet's interior and processes occurring within its domain. Comparing Earth's magnetosphere with those of Saturn and other planets has led scientists to a deeper understanding of the magnetic bubble that surrounds and strongly influences our planet.

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.

Diagram of Saturn's Magnetosphere
The magnetosphere is an area of space, around a planet, that is controlled by that planet's magnetic field. Saturn is surrounded by a giant magnetic field, lined up with the rotation axis of the planet.
In addition to their magnetic effects, magnetospheres produce radio waves. Saturn's magnetic field is far weaker than Jupiter's, and unlike the intense Jovian radio emissions, Saturn's radio signals are not powerful enough to be detected from Earth. Cassini and previous spacecraft visiting Saturn measured a type of radio emissions that scientists expected to reveal the rotation period of Saturn's magnetic field. This rotation rate is considered to be true length of the planet's day, since gas giants have no solid surface and their cloud bands move at various speeds.

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.