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

TL;DR

This study reports the first detection of millimetre thermal emission from comet 8P/Tuttle's nucleus from Earth, providing insights into its size and thermal properties using multi-wavelength observations.

Contribution

It is the first to detect millimetre thermal emission from a cometary nucleus from Earth and constrains its thermal inertia and emissivity using combined observations and shape modeling.

Findings

Millimetre thermal emission of comet 8P/Tuttle detected for the first time since 1997.

Thermal inertia constrained to be lower than ~10 J K-1 m-2 s-1/2.

Emissivity estimated to be lower than 0.8, indicating sub-surface contribution.

Abstract

Little is known about the physical properties of cometary nuclei. Apart from space mission targets, measuring the thermal emission of a nucleus is one of the few means to derive its size, independently of its albedo, and to constrain some of its thermal properties. This emission is difficult to detect from Earth but space telescopes (Infrared Space Observatory, Spitzer Space Telescope, Herschel Space Observatory) allow reliable measurements in the infrared and the sub-millimetre domains. We aim at better characterizing the thermal properties of the nucleus of comet 8P/Tuttle using multi-wavelentgh space- and ground-based observations, in the visible, infrared, and millimetre range. 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. 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 spheres shape model derived from Hubble Space Telescope observations, we constrained the thermal properties of the nucleus. Our millimetre observations are best match with: i) a thermal inertia lower than ~10 J K-1 m-2 s-1/2, ii) an emissivity lower than 0.8, indicating a non-negligible contribution of the colder sub-surface layers to the outcoming millimetre flux.