There is no “cometopause” at comet Halley

Abstract

Immediately after the flybys at comet Halley by a fleet of spacecraft in 1986, Gringauz et al. (1986a) reported the detection by the Vega‐ 2 spacecraft of a chemical and sharp plasma boundary, which they named the “cometopause,” at a distance of ∼1.6 × 10 5 km from the nucleus. Gringauz and Verigin (1991) presented the “cometopause” as a permanent feature of the solar wind ‐ Halley type comet interaction at ∼1 UA from the Sun. This permanent boundary presumably separates an upstream region dominated by the solar wind from the downstream region where heavy cometary ions dominate. We present here the analysis of the results of the Giotto positive ion cluster composition analyzer ‐ Rème plasma analyzer (PICCA‐RPA2) ion mass spectrometer and electron electrostatic analyzer ‐ Rème plasma analyzer (EESA‐RPA1) electron spectrometer data, which clearly show that there is no such boundary at comet Halley.