Giotto magnetic-field results on the boundaries of the pile-up region and the magnetic cavity

Summary

The application of the minimum-variance-technique to the magnetic field measurements obtained during the Giotto encounter at comet P/Halley has led to the following results on the inner plasma boundaries in the magnetoplasma surrounding the comet:

• (a) Modelling the boundary of the magnetic pile-up region firstly by a half-sphere cylinder combination and secondly by a paraboloid with the axes of both surfaces aligned with the aberrated solar wind has led to stand-off distances towards the aberrated solar wind of 143 000 km and 215 000 km, respectively. These can be considered as extreme case without flaring and with strong flaring, respectively.

The axis of symmetry had a transverse offset of about 80 000 km from the nucleus.

• (b) The ionopause i. e. the outer boundary of the magnetic cavity region had either a smooth surface of radius 4600 km displaced from the nucleus by 1500 km or, alternatively, it had no average displacement but strong ripples aligned with the aberrated solar wind direction and a wavelength of at least 200 km. Combinations are also possible.

The ionopause must be a tangential discontinuity thereby containing further evidence of the null magnitude of the cavity field.