[en] 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 C_3, were detected. C_2 and NH_2 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 C_2 production increases more rapidly with decreasing solar distance than CN. As one consequence the C_2/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. (\cite{AMSOB}) 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. based on observations obtained at ESO La Silla within ESO programmes No. 57.F-0290 and 58.F-0413
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Schulz, R.; ESA Space Science Department, ESTEC, Postbus 299, 2200 AC Noordwijk, The Netherlands
Arpigny, Claude ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)
Manfroid, Jean ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)
Stuewe, J. A.; Astronomisches Institut, Ruhr-Universitaet Bochum, D-44780 Bochum, Germany
Tozzi, G. P.; Osservatorio Astrophisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy