Saturn’s ULF foreshock boundary.

ANDRÉS NAHUEL; DANIEL O. GOMEZ; CESAR BERTUCCI; CHRISTIAN MAZELLE

San Francisco

Congreso; American Geophysical Union, Fall Meeting 2011; 2011

American Geophysical Union

Although the solar wind is highly supersonic, intense ULF wave activity has been detected in regions just upstream of the bow shocks of magnetized planets. This feature was first observed ahead of the Earth’s bow shock, and the corresponding region was called the ULF foreshock, which is embedded within the planet’s foreshock. The properties as well as the spatial distribution of ULF waves within the Earth’s foreshock have been extensively studied over the last three decades and have been explained as a result of plasma instabilities triggered by solar wind ions backstreaming from the bow shock. Since July 2004, the Cassini spacecraft has characterized the Saturnian plasma environment including its upstream region. The purpose of the present study is to characterize the properties of waves observed in Saturn’s ULF foreshock by the Vector Helium Magnetometer (VHM) onboard Cassini from Saturn Orbit Insertion until August 2005. The amplitude of these waves is usually comparable to the mean magnetic field intensity, while their frequencies are comparable or somewhat smaller than the local proton cyclotron value. We use the single spacecraft techniques already used for the Earth’s foreshock to identify the outer boundary of Saturn’s ULF foreshock. Our results show the existence of a clear boundary for Saturn’s ULF foreshock, with characteristics similar to the Earth’s foreshock.