May 3, 2013
Cassini Sees Seasonal Plasma Changes On Saturn
Lee Rannals for redOrbit.com — Your Universe Online
NASA's Cassini spacecraft has helped shed light on one way the bubble of charged particles around Saturn changes with the planet's seasons.
Earth has a magnetosphere like Saturn, and the latest results may help scientists better understand variations in it and the Van Allen radiation belts, which both affect things from space flight safety to satellite and cell phone communications. Researchers wrote in the Journal of Geophysical Research their findings help provide an important clue in solving a riddle about the planet's naturally occurring radio signal.
The team looked at Cassini data collected around Saturn from July 2004 to December 2011, examining "flux tubes." These tubes funnel charged particles in towards Saturn. The scientists found the occurrence of the tubes correlates with radio wave patterns in the northern and southern hemisphere, depending on the season. This effect is roughly similar to how Earth's northern lights appear more frequently in the spring and fall.
The scientists used radio emissions to help determine Saturn's rotation period, which is a technique used in the past to measure Jupiter's rotation period. The new results could help scientists understand why these signals vary.
Scientists have known for some time Saturn's magnetospheric processes are linked together, but they did not understand how they were linked. The researchers found during winter and in the northern hemisphere, the occurrence of flux tubes correlates with the Saturn kilometric radiation (SKR) period originating in the northern hemisphere. A similar flux tube and SKR correlation was made in the southern hemisphere during southern winter.
Saturn's magnetosphere has also helped make another great observation recently. Researchers reported back in February Cassini detected subatomic particles in Saturn's magnetosphere that could have come from a supernova. They wrote in the journal Nature Physics Cassini picked up particles that had been accelerated to ultra-high energies in a blast of solar wind around Saturn. This discovery could help scientists hone in on how the acceleration of electrons in very strong shocks with "Mach numbers" depend on the angle between the magnetic field and a vector at right angles to the shock front.
“The Cassini observations have given us a glimpse of a process never before seen directly, providing new information on how high-energy particles, like cosmic rays, are accelerated to such high velocities by magnetic fields throughout the Universe,” says Nicolas Altobelli, one of ESA´s Cassini project scientists.