Comparison of observed and calculated implanted ion distributions outside comet Halley's bow shock

This paper compares calculated and measured energy spectra of implanted H + and O + ions on the assumption that the pickup geometry is quasi‐parallel and about 1% of the waves generated by the cometary pickup process propagate backward (toward the comet). The model provides a good description of the implanted O + and H + energy distribution near the pickup energies. The thickness of the implanted ion velocity distribution shells was nearly constant between 2.50×10 6 km and 1.20×10 6 km (just outside the shock) along the inbound Giotto trajectory. The explanation is that the velocity diffusion coefficient and characteristic diffusion time vary approximately as 1/ r and r , respectively, and therefore their product (which determines the velocity shell thickness) remains nearly constant.