The effect of Kepler orbits on the distribution of neutrals and ions around comet Halley

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The effect of Kepler orbits on the distribution of neutrals and ions around comet Halley

Daly, P.W. / Jockers, K.

Abstract The densities of neutral particles emitted isotropically with a fixed initial relative speed from comet P/Halley have been calculated out to distances of 24 Gm (≡ 24 × 10⁶ km) by finding their Kepler orbits about the Sun. Furthermore, ion fluxes along the Giotto inbound path are determined from the upstream neutral densities. The results are compared to those that would be obtained if one assumes that the neutrals possess a spherically symmetric, 1/R ² distribution. It is shown that for initial speeds of 1 km s⁻¹, typical for water group neutrals, the resulting ion flux along the Giotto trajectory falls off with distance less steeply than otherwise expected. For speeds of 8 and 20 km s⁻¹, representing H atoms, the results are very close to those of the spherically symmetric model. However, if radiation pressure is included, then the slower component of H atoms and the consequence H⁺ ions cannot be observed by Giotto beyond 8 Gm.