Earth-based detection of the millimetric thermal emission from the nucleus of comet 8P/Tuttle
Résumé
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 similar to 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.