Solar wind flow through the comet P/Halley bow shock

Abstract

The bow shock of a comet is formed by the interaction of three different particle populations; solar wind ions, cometary ions and electrons. We follow the behaviour of the solar wind protons through the Giotto inbound shock crossing at comet P/Halley. A foreshock boundary is seen at ~ 1.4 106 km where the level of solar wind fluctuations increases substantially. The shock itself is seen some 2.5 105 km closer. It is a complex structure with high-amplitude waves in the cometary ion foot of the shock preceding a permanent drop in the solar wind speed. The width of the shock structure is ~ 40,000 km. There is evidence for a further excursion back into the cometary ion foot after the initial shock crossing. The cometary ion density is inferred from the solar wind speed changes and is compared with measurements.