Saturn's moons rip through its radiation belts

The moons around Saturn have a much larger effect on the planet's radiation belts than solar winds.


The intensity of the bands of radiation around Saturn dropped in 2012 much faster than would be expected if the solar wind was responsible
Credit: NASA/JPL/Space Science Institute


The radiation belts surrounding Saturn are split apart by the planet’s many moons, according to the latest interpretation of data from NASA’s Cassini spacecraft.

Radiation belts encircle several worlds in our Solar System, including Earth and Saturn, and are created by very energetic particles becoming caught in the planets’ magnetic fields.

On Earth, the bands’ intensity is governed by the solar wind - a stream of charged particles emanating from the Sun's surface – its ebbs and flows affecting the belts both directly and indirectly.

Around Saturn, however, moons seem to be the prominent power.


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While observing Saturn, Cassini detected that its belts ranged from the inner ring out to the moon Tethys, some 285,000km into space, also encompassing many other moons.

However, the belt’s intensity was not uniformly spread within this gap. Instead, the moons appeared to have carved spaces in the belt as they soak up the charged particles, preventing them from diffusing inwards, as happens around Earth.

“This creates areas in the radiation belt which are completely isolated from one another,” says Elias Roussos from the Max Plank Institute for Solar System Research.


NASA's Cassini mission revealed Saturn to us like never before. Scientists will be analysing its data and drawing conclusions for years to come.
Credit: NASA/JPL-Caltech/Space Science Institute


Between 2010 and 2012, the researchers found that the changes in the solar wind didn’t match what was happening within Saturn’s belts at the time.

The Sun may still have been responsible for the alterations, but it is the ultraviolet radiation that affects the belt intensity rather than the solar wind.

The observations were only possible as the probe spent over 13 years around the planet, meaning it could watch the planet throughout an entire 11-year solar cycle and observe the effect this had on the belts.

“If Cassini’s mission to the Saturn system had ended after four years, as initially planned, we would never have been able to achieve these results,” says Roussos.

Not only will the observations help astronomers understand the radiation belts around our own planet, and how they could affect spacecraft in orbit, but it will also increase understanding of how the belts might behave around other planets and exoplanets.

“Our analyses also remind us how strongly the properties of the radiation belts depend on the structure of the particular planet system, that is, the position and number of moons for the case of Saturn,” says Roussos.


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