Expansion Velocity and Temperatures of Gas and Ions Measured in the Coma of Comet p/ Halley
Berthelier, J. J.; Eberhardt, P.; Krankowsky, D.; Hodges, R. R.; Dolder, U.; Lammerzahl, P.; Woweries, J.; Stubbemann, U.; Hoffman, J. H.; Illiano, J. M.; Herrwerth, I.; Shulte, W.
Germany, United States, France, Switzerland
Abstract
In situ measurements of flow velocity and temperature in the inner coma were obtained from ram energy spectra of molecules and ions observed by the NMS experiment onboard the Giotto probe to comet Halley. Radial flow speed was (800 ± 50) m s-1 at distances from the nucleus between 1000km and 4000 km. Whereas ions became stagnant just outside the contact surface (located near 4500 km), the outflow of water vapour even accelerated and was above 1 km s-1 at 30000 km. Ion temperatures were around 200 K inside the contact surface where the plasma is collisionally coupled to the gas; at this boundary ion temperature rises by about 1000 K and then further increases to reach about 5000 K at 15000 km. Gas temperature remains below 300-500 K over this range of distances. A near zero volt spacecraft potential was inferred.