The D/h Ratio in Water from Comet p/ Halley
Berthelier, J. J.; Eberhardt, P.; Krankowsky, D.; Hodges, R. R.; Schulte, W.; Dolder, U.; Lammerzahl, P.; Hoffman, J. H.; Illiano, J. M.
Switzerland, Germany, United States, France
Abstract
The neutral gas mass spectrometer on the Giotto spacecraft made neutral and ion composition measurements with a high mass resolution. From a preliminary evaluation of the ion data within the contact surface the authors obtain for the water in Halley an 18O abundance of 18O/16O = 0.0023±0.0006 and for the D/H ratio 0.6×10-4 ≤ D/H ≤ 4.8×10-4. The cometary 18O abundance is within error limits identical to the terrestrial one. The D/H ratio in Halley is definitely not compatible with the D/H in gaseous hydrogen of the protosolar nebula or the Jovian and Saturnian atmospheres. It is in the range observed for hydrogen in solar system objects which acquired their hydrogen as part of volatile molecules, e.g. as ices.