Overshoots in planetary bow shocks

Abstract

An overshoot in the magnitude of the magnetic field is shown here to be a consistent feature of supercritical collisionless shocks, Mach number ≳3, throughout the Solar System. Although the variability of the solar wind at 1 AU allows us to study the Earth's bow shock over a wide range of β, the ratio of thermal pressure to magnetic pressure, the Mach number of the solar wind at 1 AU varies over a relatively narrow range. Data from Jupiter and Saturn allow us to study the bow shock at high Mach numbers rarely, if ever, observed at Earth. These combined planetary data show that the planetary bow shocks, at least as characterized by their overshoots, form part of a continuum, differences being dependent mainly on the varying solar wind conditions at each of the planets. The overshoot magnitude is found to increase both with β and magnetosonic Mach number. However, it is the radial variation of Mach number which causes the overshoot in the jovian and saturnian bow shocks to be much greater than in the terrestrial shock.