Earth-based detection of the millimetric thermal emission from the nucleus of comet 8P/Tuttle^⋆

¹ Istituto di Radioastronomia – INAF, via Gobetti, 101 Bologna Italy
e-mail: boissier@ira.inaf.it
² ESO, Karl Schwarzschild Str. 2, 85748 Garching bei Muenchen, Germany
³ Institut de radioastronomie millimétrique, 300 rue de la piscine, Domaine universitaire, 38406 Saint Martin d’Hères, France
⁴ Laboratoire d’Astrophysique de Marseille, Université de Provence, CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁵ LESIA, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France

Received: 3 November 2010
Accepted: 17 January 2011

Abstract

Context. Little is known about the physical properties of cometary nuclei. Measuring the thermal emission of a nucleus is one of the few means of deriving its size, independently of its albedo, and constraining some of its thermal properties. This emission is difficult to detect from Earth but space telescopes, such as th Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory, allow reliable measurements to be made in the infrared and the sub-millimetre domains.

Aims. We attempt to characterize more accurately the thermal properties of the nucleus of comet 8P/Tuttle using multiwavelength space- and ground-based observations, in the visible, infrared, and millimetre range.

Methods. We used the Plateau de Bure Interferometer to measure the millimetre thermal emission of comet 8P/Tuttle at 240 GHz (1.25 mm) and analysed the observations with the shape model derived from Hubble Space Telescope observations and the nucleus size derived from Spitzer Space Telescope observations.

Results. We report on the first detection of the millimetre thermal emission of a cometary nucleus since comet C/1995 O1 Hale-Bopp in 1997. Using the two contact-sphere shape model derived from Hubble Space Telescope observations, we constrain the thermal properties of the nucleus. Our millimetre observations are most accurately reproduced by assuming: i) a thermal inertia lower than  ~10 J K^-1 m^-2 s^−1/2, and ii) an emissivity lower than 0.8, which is indicative of a non-negligible contribution of the colder sub-surface layers to the outcoming millimetre flux.