Cassini at Saturn's bow shock: Shedding light on cosmic particle accelerators

Astronomy Unit Seminars
Dr. Adam Masters (Imperial College)
David Burgess
February 6th, 2015 at 14:30
GO Jones Room 610

Shock waves are widespread in collisionless space plasmas throughout the Universe. How particles are accelerated at these shocks has been the subject of much research attention. The dominant source of the high-energy particles that pervade our Galaxy (cosmic rays) is thought to be the high-Mach number collisionless shocks that form around young supernova remnants, but it is unclear how much the lower Mach number collisionless shock waves frequently encountered by spacecraft in Solar System space plasmas can tell us about particle acceleration in the higher Mach number regime. Here we introduce recent studies of the shock wave that stands in the solar wind in front of the planet Saturn (Saturn’s bow shock), based on Cassini spacecraft observations. These investigations have defined a new direction of shock physics research, with the potential to bridge the gap between Solar System and astrophysical shocks. Studies to date have confirmed that Saturn’s bow shock is one of the strongest shocks in the Solar System, and a recent discovery indicates that electron acceleration at high-Mach numbers may occur irrespective of the upstream magnetic field geometry. This is important because astrophysical shocks can often only be studied remotely via emissions associated with accelerated electrons. We discuss ongoing work and future directions of this emerging sub-field.