Bow shock analysis at comets Halley and Grigg‐Skjellerup

Abstract

Abstract. The interaction of an active comet with the solar wind is effected by the pickup of heavy cometary ions over extended regions of space. It was predicted before any spacecraft encounters with comets that a bow shock would form at a critical point in the mass-loaded flow. Here we present an analysis of the results from Giotto's encounters of comets Halley and Grigg-Skjellerup on the plasma structure of the bow shock regions at the two comets. This is achieved in a joint analysis of data on solar wind and cometary ions, magnetic field, and electrons. We find that these mass-loading shocks are among the most complex in the solar system with heavy cometary ions dominating the component pressures. Results of Mach number calculations at Halley support earlier interpretations that bow shocks were, indeed, seen with possible solar wind disturbance inbound. At Grigg-Skjellerup, Mach number results support the interpretation of a "wave" inbound and a "shock" outbound; both features also occur near to the expected location for a bow shock. A weak correlation between magnetic field strength and electron density is noted at the Grigg-Skjellerup outbound shock in agreement with quasi-perpendicular hybrid simulations.

2D hybrid simulations of the solar wind interaction with a small scale comet in high Mach number flows

“…Halley, with the largest neutral production rate of the three, affected SW plasma out to distances of 5 x 106 km [Gringauz et at., 1986], compared to a pickup ion gyroradius of • 104kin [SzegS, 1988], and had several plasma boundaries, some open to interpretation. Grigg-Skjellerup represented the interaction at a much smaller source, and consequently was found to have fewer boundaries and a weaker shock-like interaction, such that on the inbound pass it was interpreted as a bow "wave" [Coates et al, 1997].…”

Multipoint observations of plasma phenomena made in space by Cluster

“…The Earth's bow shock was discovered in 1964 (Ness et al 1964) and subsequently, bow shocks have been observed at all of the visited planets (Treumann and Jaroschek 2008), at comet Halley (Coates et al 1997), and, most recently, at the termination shock that separates the solar system from interstellar space (see for example, Stone et al 2005). Soon after the Earth's bow shock was discovered, Kaufmann (1967) noted that some shock transitions from upstream to downstream were sharp and well defined, while others were noisy and accompanied by large magnetic fluctuations.…”

Pickup Particle Acceleration at Comets, Moons and Magnetospheres

“…The mass loading associated with these slows the plasma enough that eventually a bow shock forms. Pickup ions play a key role at the bow shock [26,27,28].…”