Orientation, location, and velocity of Saturn's bow shock: Initial results from the Cassini spacecraft

摘要

The Cassini spacecraft commenced its tour of the planet Saturn on 1 July 2004 (GMT). During the insertion orbit, the Cassini magnetometer (MAG), radio/plasma wave experiment (RPWS), and plasma spectrometer (CAPS) obtained in situ measurements of the magnetic field and plasma conditions associated with Saturn's environment. Analysis of the magnetic field data indicate that Cassini repeatedly crossed a mainly quasi-perpendicular bow shock boundary on both the inbound (post-dawn) and outbound (predawn) legs. Modeling of the bow shock and magnetopause crossing positions shows evidence for a magnetospheric compression during Cassini's immersion in the magnetosphere. The magnetic signatures of the bow shock crossings show the clearly defined “overshoot” and “foot” regions associated with the quasi-perpendicular geometry. The duration of the shock foot, considered in combination with the RPWS and CAPS solar wind electron parameters upstream of the bow shock crossings, indicates that the length scale for the bow shock ramp at Saturn is about an ion inertial length. This is consistent with multispacecraft observations of the spatial scale of the Earth's shock foot region. The data are generally consistent with Saturn bow shock velocities up to ～400 km s?1 and shock structures governed by ion dynamics.