Giotto / IMS Observations of Ion Flow Velocities and Temperatures Outside the Magnetic Cavity of Comet p/ Halley
Schwenn, R.; Balsiger, H.; Goldstein, B. E.; Goldstein, R.; Fuselier, S. A.; Ip, W. H.; Neugebauer, M.; Rettenmund, U.; Rosenbauer, H.; Shelley, E. G.; Drake, J.
United States, Switzerland, Germany
Abstract
Fluid parameters for He2+ ions obtained from the Giotto Ion Mass Spectrometer HERS sensor are presented; also investigated are proton densities and velocities and thermal speeds of protons, alpha particles, and heavy ions in the hour before closest approach. A bow shock transition lasting ten minutes is observed. A region of enhanced He2+ ion densities, and velocity, and decreased temperature is observed from 20:26 to 21:45. Sharp decreases in the proton density are observed at 23:30 and at 23:41; there are also sharp drops in alpha particle density and temperature at 23:30. There is a relative flow velocity between alpha particles and oxygen ions of approximately 20 km s-1 during a period roughly from 22:55 to 23:10; by 23:30 the difference in flow velocity is less than the experimental uncertainities.