* Astronomy

New Transient Radiation Belt Discovered at Saturn
Scientists using the Cassini spacecraft's Magnetospheric Imaging instrument (MIMI) have detected a new, temporary radiation belt at Saturn, located around the orbit of its moon Dione at about 377 000 km from the centre of the planet. The discovery will be presented at the European Planetary Science Congress in Potsdam by Dr Elias Roussos on Monday 14 September.
Radiation belts, like Earth's Van Allen belts, have been discovered at Jupiter, Saturn, Uranus and Neptune. However, to date, it has only been possible to observe the variability of their intensity at Earth and Jupiter. Now that Cassini has been orbiting Saturn for more than five years, it has been possible to assess for the first time changes in Saturn's radiation belts.
An international team of astronomers made the discovery analysing data from the MIMI's LEMMS sensor, which measures the energy and angular distribution of charged particles in the magnetic bubble that surrounds Saturn.

"The most dramatic changes have been observed as sudden increases in the intensity of high energy charged particles in the inner part of Saturn's magnetosphere, in the vicinity of the moons Dione and Tethys. These intensifications, which could create temporary satellite atmospheres around these moons, occurred three times in 2005 as a response to an equal number of solar storms that hit Saturn's magnetosphere and formed a new, temporary component to Saturn's radiation belts" - Dr Elias Roussos.

The new belt, which has been named 'the Dione belt,' was only detected by MIMI/LEMMS for a few weeks after each of its three appearances. The team believe that newly formed charged particles in the Dione belt were gradually absorbed by Dione itself and another nearby moon, named Tethys, which lies slightly closer to Saturn at an orbit of 295 000 km.
Unlike the Van Allen belts around the Earth, Saturn's radiation belts inside the orbit of Tethys are very stable, showing negligible response to solar storm occurrences and no variability over the five years that they have been monitored by Cassini.
Interestingly, it was found that the transient Dione belt was only detected outside the orbit of Tethys. It appeared to be clearly separated from the inner belts by a permanent radiation gap all along the orbit of Tethys.

"Our observations suggest that Tethys acts as a barrier against inward transport of energetic particles and is shielding the planet's inner radiation belts from solar wind influences. That makes the inner, ionic radiation belts of Saturn the most isolated magnetospheric structure in our solar system" - Dr Elias Roussos.

The radiation belts within Tethys's orbit probably arise from the interaction of the planet's main rings and atmosphere and galactic cosmic ray particles that, unlike the solar wind, have the very high energies needed to penetrate the innermost Saturnian magnetosphere. This means that the inner radiation belts will only vary if the cosmic ray intensities at the distance of Saturn change significantly.

"Outside the orbit of Tethys, the variability of Saturn's radiation belt might be enhanced in the coming years as we start approaching the solar maximum. If solar storms occur frequently in the new solar cycle, the Dione belt might become a permanent, although highly variable, component of Saturn's magnetosphere, which could affect significantly Saturn's global magnetospheric dynamics" - Dr Elias Roussos.

Source: European Planetology Network

Saturns rings still puzzle scientists
Saturn's rings have fascinated scientists ever since Italian astronomer Galileo Galilei first spotted them through one of his telescopes in the 17th century. But just how the icy rings came into being remains a mystery that has only deepened with each new scientific finding.
Astronomers now know that the planet hosts multiple rings that consist of roughly 35 trillion-trillion tons of ice, dust and rock. The Cassini spacecraft and its Voyager predecessors have also spotted changing ring patterns, partially formed ring arcs and even a moon spewing out icy particles to form a new ring. All of this suggests that the rings have constantly evolved over time.

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Equinox to reveal Saturn secrets
Planetary scientists are keenly observing an equinox on Saturn on 11 August, in a bid to learn more about the gas giant's ring system.
A planet's equinox comes twice a year when the Sun crosses its equator, making day and night the same length.
It takes Saturn nearly 30 Earth years to orbit the Sun, so this is the first equinox since 1994.

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Saturn ring plane crossing on August 11, 2009.

All planets in our solar system wobble on their axes to some extent. This change of attitude eventually places a planet's equator directly in line with the photons of light streaming in from the sun. This is called "equinox," and on Earth it occurs every year about March 21 (spring equinox) and September 22 (autumnal equinox). On Saturn, it occurs twice during each 29 Earth-year-long orbit around the sun (about every 15 years).

"Saturn has been performing the "ring plane crossing" illusion about every 15 years since the rings formed, perhaps as long as 4.5 billion years ago, so by now it is pretty good at it.  The magician's tools required to perform this trick are pure sunlight, a planet that wobbles, and a main ring system that may be almost 200-thousand miles wide, but only 30 feet thick" - Linda Spilker, deputy project scientist for the Cassini Saturn mission at NASA's Jet Propulsion Laboratory in Pasadena, California.

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