First results from the Giotto magnetometer experiment during the P/Grigg-Skjellerup encounter

The Giotto magnetic field experiment has provided the first magnetic field data on the interaction between the solar wind and a low gas production comet, P/Grigg-Skjellerup. Waves produced by ion pick-up instabilities have been observed throughout the interaction region with particularly simple waveforms at large distances and a rich phenomenology. A bow shock has been observed outbound only, whereas inbound a change in the character of the wave fields occurred without a jump in the magnetic field vector. The inbound and outbound crossings of the bow wave and shock at 19900 km and 25400 km from the nucleus, respectively, imply a neutral gas production rate of (6.7 ± 1.6) × 10 27 s −1 . A magnetic field cavity of the comet was not crossed