H2O + ions in comets: models and observations |
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| Institution: | 1. Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS - Université Bourgogne Franche-Comté, 9 Av. A. Savary, BP 47870, Dijon Cedex F-21078, France;2. Groupe de Spectrométrie Moléculaire et Atmosphérique (GSMA), CNRS UMR 7331, Université de Reims Champagne-Ardenne, U.F.R. Sciences Exactes et Naturelles, Moulin de la Housse B.P. 1039, Reims Cedex 2 51687, France;1. INAF-IAPS, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, via del Fosso del Cavaliere, 100, 00133 Rome, Italy;2. LESIA, Observatoire de Paris, LESIA/CNRS, UPMC, Université Paris-Diderot, F-92195 Meudon, France;3. Institute for Planetary Research, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany;4. Université Grenoble Alpes, CNRS, IPAG, Grenoble, France;5. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA;6. Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, Lecce, Italy |
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| Abstract: | An improved magnetohydrodynamic (MHD) model with chemistry is presented. The analysis of the source and sink terms for H2O + shows that for small comets up to 11% of water molecules are finally ionized. For large comets (such as Halley) this fraction decreases to less than 3%. From the MHD scaling laws a similarity law for the individual ion densities is deduced which takes into account that the mother molecules are depleted by dissociation. This is applied to H2O + ions. Radial density profiles from model calculations, observations by Giotto near comet Halley, and ground based observations of three comets confirm this scaling law for H2O + ions. From the similarity law for the density a scaling law for the column density is derived which is more convenient to apply for ground based observations. From these scaling laws methods are derived which allow the determination of the water production rate from the ground based images of the H2O + ions. Finally, the two dimensional images of model column densities are compared with observations. |
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