EDP Sciences
Free access
Volume 412, Number 3, December IV 2003
Page(s) 879 - 891
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20031496

A&A 412, 879-891 (2003)
DOI: 10.1051/0004-6361:20031496

Activity on the surface of the nucleus of comet 46P/Wirtanen

O. Groussin and P. Lamy

Laboratoire d'Astrophysique de Marseille, BP 8, 13376 Marseille Cedex 12, France
(Received 4 March 2003 / Accepted 6 May 2003)

We present a thermal model of the nucleus of comet 46P/Wirtanen, constrained by the temporal variations of the water production rate, in order to understand the activity on its surface. We consider a spherical nucleus with a macroscopic mosaic of small and numerous active and inactive regions. At heliocentric distances $r_{\rm h}$  > 1.5 AU, the active regions represent 5-15% of the surface. At ~1.5 AU, a rapid increase takes place and the active fraction reaches 70 to 100% in about 10 days, and then remains approximately constant up to perihelion where $Q_{\rm {H_2O}}=1.3\pm0.3\times10^{28}$ molecule s -1. Post-perihelion, this fraction returns to ~10%. The model is consistent with a geometric albedo $\leq$0.06. A refractory crust likely forms post-perihelion and can explain the variations of the activity over an orbit. Finally, we derived an erosion of ~0.5 m per revolution and a remaining lifetime for the nucleus of several hundred revolutions.

Key words: comets: individual: 46P/Wirtanen

Offprint request: O. Groussin, olivier.groussin@oamp.fr

© ESO 2003

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