EDP Sciences
Free Access
Volume 419, Number 1, May III 2004
Page(s) 375 - 383
Section Planets and planetary systems
DOI https://doi.org/10.1051/0004-6361:20040073

A&A 419, 375-383 (2004)
DOI: 10.1051/0004-6361:20040073

The nuclei of comets 126P/IRAS and 103P/Hartley 2

O. Groussin1, P. Lamy1, L. Jorda1 and I. Toth1, 2

1  Laboratoire d'Astronomie Spatiale, BP 8, 13376 Marseille Cedex 12, France
2  Konkoly Observatory, PO Box 67, Budapest 1525, Hungary

(Received 6 May 2003 / Accepted 15 January 2004 )

We report the detection of the nucleus of 126P/IRAS and 103P/Hartley 2 with the Infrared Camera of the Infrared Space Observatory (ISOCAM). 126P/IRAS was observed on 12 November 1996, when it was at $r_{\rm h}=1.71$ AU from the Sun and $\Delta=1.32$ AU from the Earth. 103P/Hartley 2 was observed on 5 February 1998, when it was at $r_{\rm h}=1.21$ AU from the Sun and $\Delta=0.91$ AU from the Earth. The observations were performed with the broadband LW10 filter centered at 11.5  $\mu$m. The spatial resolution was adequate to separate the thermal emission of the nuclei from that of their respective comae. We combined the ISOCAM observations with measured water production rates, using a model that considers a spherical nucleus with a macroscopic mosaic of small and numerous active and inactive regions, and we derived a radius of $1.57\pm0.14$ km and an active fraction at perihelion of $0.11\pm0.03$ for 126P/IRAS, and a radius of $0.71\pm0.13$ km and an active fraction of ~1 at perihelion and $0.30\pm0.11$ at 1.11 AU post-perihelion for 103P/Hartley 2. These two examples illustrate the large diversity of activity pattern that exists among cometary nuclei.

Key words: comets: individual: 126P/IRAS -- comets: individual: 103P/Hartley 2 -- comets: general

Offprint request: O. Groussin, grousssin@astro.umd.edu

© ESO 2004