# ESA Science & Technology - Publication Archive

## Publication archive

## Publication archive

Published: 05 January 2001

Published: 05 January 2001

Published: 05 January 2001

Published: 05 January 2001

Published: 01 December 1999

Published: 02 May 1999

Published: 02 May 1999

Published: 02 May 2000

Published: 01 January 1999

Published: 02 May 1997

_{60}. Four groups of the hydrocarbons are considered : Polyacetylenes (PA), Polyvinyles (PV), Vinylacetylenes (VA) and Allenes (Polyenes).

Published: 02 April 1997

Published: 15 December 1999

Bulletin of the American Astronomical Society, Vol 31, No. 4 (DPS)

Published: 02 September 1999

Published: 02 August 2000

Published: 01 January 2000

^{28}molecules s

^{-1}at perihelion, assuming a radius of 600 m. The calculated gas flux of water is within the order of measured values for comet 46P/Wirtanen. But our calculated values are maximum gas fluxes at noon—not averaged over one cometary day or taking the lesser insolation at the polar areas into account. Therefore, we conclude that either the radius of comet 46P/Wirtanen may be much larger than the accepted value of 600 m. A radius in the order of 2 km seems more likely to explain the measurements. Or, an other possibility could be that water-ice particles are blown off from the surface like dust particles. This may also increase the effective surface area of sublimation.

Published: 22 November 1998

^{-4}) is 10-20 times larger then the D/H ratio in the solar nebula. Therefore the cometary water had to originate in a giant molecular cloud, where the HDO is enriched by ion-molecule reactions.

Published: 02 July 1999

Geophysical Research Abstracts, Vol. 1, No. 3 (EGS)

Published: 01 March 1999

_{2}O

^{+}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 H

_{2}O

^{+}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 H

_{2}O

^{+}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 H

_{2}O

^{+}ions. Finally, the two dimensional images of model column densities are compared with observations.

Published: 03 October 1998

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