To CO and N2 Abundance in Comet p/ Halley
Berthelier, J. J.; Eberhardt, P.; Krankowsky, D.; Hodges, R. R.; Schulte, W.; Dolder, U.; Lammerzahl, P.; Woweries, J.; Stubbemann, U.; Hoffman, J. H.; Illiano, J. M.
Switzerland, Germany, France, United States
Abstract
A preliminary evaluation of the mass 28 amu/e signal observed in the neutral mode of the Giotto neutral gas mass spectrometer (NMS) is presented. At 1000 km from the nucleus the authors obtain for the CO number density n(CO)/n(H2O) ≤ 0.07. The production rate of CO as parent molecule directly from the nucleus is thus less than 7% of the H2O production rate. However, CO is also produced from an extended source in the inner coma (R < 20,000 km) and at 20,000 km from the nucleus the authors obtain for the total equivalent CO production rate 0.05 ≤ Q(CO)/Q(H2O) ≤ 0.15. For N2 an upper limit Q(N2)/Q(H2O) ≤ 0.1 is derived. No parent molecule for the CO could be identified which would be in agreement with the NMS measurements. It is proposed that CO or a very short-lived parent is released in the coma from cometary dust grains, such as the "CHON" particles.