Ion composition and dynamics at comet Halley
Abstract
The ion mass spectrometer aboard the Giotto spacecraft measured the composition and velocity distributions of cometary ions at distances of ~7.5×l06 to ~1,300 km from the nucleus of comet Halley. Well outside the bow shock, pick-up cometary H+ ions were found in a diffuse shell-like distribution. Heavier ions (C+, H2O+-group, CO+ and S+) with similar distributions have been identified at <=3×l05 km. Solar-wind He2+ was found throughout the coma to as close as ~5,000 km; He+ produced by charge exchange was seen inside ~2×105 km. Deeper within the coma the main cometary hot-ion species identified were H+, H2+, C+, O+, OH+, H2O+, H3O+, CO+ and S+. A pile-up of heavy cometary ions was found at ~104 km from the nucleus. Giotto crossed the contact surface at ~4,600 km, based on changes in ion flow velocity and temperature. Inside, ion temperatures as low as ~340 K and outflow velocities of ~1 km s-1 were found. Outside the contact surface ion densities vary as r-2, with a transition to an r-l dependence approximately at the contact surface. A large C+ abundance throughout the coma indicates an unexpected direct source of atomic carbon. The nitrogen abundance, on the other hand, is relatively low.
- Publication:
-
Nature
- Pub Date:
- May 1986
- DOI:
- 10.1038/321330a0
- Bibcode:
- 1986Natur.321..330B
- Keywords:
-
- Abundance;
- Giotto Mission;
- Halley'S Comet;
- Ion Distribution;
- Mass Spectroscopy;
- Coma;
- Ion Density (Concentration);
- Ion Temperature;
- Plasma Dynamics;
- Plasma Interactions;
- Solar Wind;
- Astrophysics; Comets;
- COMETS;
- HALLEY;
- SPACECRAFT OBSERVATIONS;
- MISSION DESCRIPTION;
- EXPERIMENTS;
- IONS;
- COMPOSITION;
- DYNAMICS;
- GIOTTO;
- ION MASS SPECTROMETER;
- VELOCITY;
- IMS;
- DISTRIBUTION;
- DISTANCE;
- COMAE;
- HYDROGEN;
- HELIUM;
- FORMATION;
- FLOW;
- CONCENTRATION;
- TEMPERATURE;
- DENSITY;
- ABUNDANCE;
- CARBON;
- NITROGEN;
- HIS;
- PLASMA;
- SOLAR WIND;
- INTERACTION;
- HERS;
- PARAMETERS;
- SPECTRA;
- HIGH ENERGY RANGE SPECTROMETER;
- HIGH INTENSITY RANGE SPECTROMETER