February 18, 2013
Cassini Spacecraft Witnesses Possible Supernova Shockwave On Saturn
Lee Rannals for redOrbit.com - Your Universe Online
For the first time, scientists from the international Cassini spacecraft have detected subatomic particles that have been accelerated to ultra-high energies in a blast of solar wind around Saturn, hinting at the possibility that the ringed planet may have experienced the aftermath of a supernova.
According to a report by the European Space Agency (ESA) that appeared recently in the journal Nature Physics, this acceleration may be the result of the strongest shock wave ever encountered on Saturn before. The Cassini spacecraft detected particles being accelerated to ultra-high energies similar to those seen in the acceleration that takes place around supernova explosions.
As supernovae ensue, debris begins to accelerate outward, creating a shock wave that can be felt from a long-distance away. Under certain magnetic field orientations and depending on the strength of the shock, particles can even be accelerated to very close to the speed of light. Very strong shocks at young supernova remnants are known to boost electrons to ultra-relativistic energies.
Space telescopes have revealed evidence in the form of X-ray emissions for accelerated electrons at supernova remnant shocks. However, these observations were made of far away objects, so the orientation of the local magnetic field has only been poorly measured.
Scientists hope to glean a better understanding of how the acceleration of electrons in very strong shocks with large "Mach numbers" depend on the angle between the magnetic field, and a vector at right angles to the shock front.
“Cassini has crossed Saturn´s bow shock hundreds of times, recording typical AlfvÃ©n Mach numbers of around 12. But during one particular crossing in early 2007, we measured a value of ~100, during which time the shock was quasi-parallel,” explained Adam Masters of the Institute of Space and Astronautical Science (ISAS) in Japan and lead author of the paper.
Masters says Cassini has given scientists the ability to study the nature of a supernova shock in situ — or where they occur — bridging the gap to distant high-energy astrophysical phenomena that are typically out of reach.
“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.
Just weeks ago, Cassini mission scientists reported that they had witnessed a large thunder and lightning storm consume itself on Saturn. This storm wrapped itself about 190,000 miles around the planet, and eventually engulfed itself. Data like this helps scientists get a better perspective of weather patterns in other worlds around our Solar System.