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Astron. Astrophys. 335, L46-L49 (1998)

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Letter to the Editor

Spectral evolution of ROSETTA target comet 46P/Wirtanen *

R. Schulz 1, C. Arpigny 2, J. Manfroid 2, J.A. Stüwe 3, G.P. Tozzi 4, K. RemborG. Cremonese 5, 6 and S. Peschke 7

1 ESA Space Science Department, ESTEC, Postbus 299, 2200 AC Noordwijk, The Netherlands
2 Université de Liège, Institut d'Astrophysique, B-4000 Liège, Belgium
3 Astronomisches Institut, Ruhr-Universität Bochum, D-44780 Bochum, Germany
4 Osservatorio Astrophisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
5 Max-Planck-Institut für Aeronomie, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau
6 Osservatorio Astronomico, Vic. Osservatorio, 5, I-35122 Padova, Italy
7 Max-Planck-Institut für Kernphysik, Postfach 10 39 80, D-69029 Heidelberg, Germany

Received 31 October 1997 / Accepted 10 January 1998


The compositional evolution of the coma of ROSETTA target comet 46P/Wirtanen was studied along its pre-perihelion orbit. At 2.34 AU the first gaseous species, CN and C3, were detected. C2 and NH2 arose at 2.0 AU. The production rate curves of gas and dust show a steep increase between 1.8 AU and 1.6 AU indicating a distinct change of the outgassing conditions. The C2 production increases more rapidly with decreasing solar distance than CN. As one consequence the C2/CN ratio strongly varies with heliocentric distance. Due to this variation a classification of 46P/Wirtanen by the taxonomy introduced by A'Hearn et al. (1995) distinguishing comets with typical abundance ratios from carbon-chain depleted comets, is impossible. It would be classified as depleted beyond about 1.6 AU whereas it would be designated typical at smaller distances. The knowledge of the unexpected changes in the activity curves of 46P/Wirtanen will help to optimize the ROSETTA mission scenario in particular with regard to science operations.

Key words: comets – coma composition – space missions

* based on observations obtained at ESO La Silla within ESO programmes No. 57.F-0290 and 58.F-0413

Send offprint requests to: R. Schulz

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© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998