title: A homogeneous nucleus for comet 67P/Churyumov-Gerasimenko from its gravity field.
abstract: Cometary nuclei consist mostly of dust and water ice. Previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67P/Churyumov-Gerasimenko on the basis of its gravity field. The mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. The gravitational point mass is GM = 666.2 ± 0.2 cubic metres per second squared, giving a mass M = (9,982 ± 3) × 10(9) kilograms. Together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. The nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9P/Tempel 1. The most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. We conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. The high porosity seems to be an inherent property of the nucleus material.
authors: Rheinisches Institut für Umweltforschung an der Universität zu Köln, Abteilung Planetenforschung, 50931 Köln, Germany.
authors: M
authors: M
authors: Pätzold
authors: Institut für Raumfahrttechnik und Weltraumnutzung, Universität der Bundeswehr München, 85577 Neubiberg, Germany.
authors: T
authors: T
authors: Andert
authors: Rheinisches Institut für Umweltforschung an der Universität zu Köln, Abteilung Planetenforschung, 50931 Köln, Germany.
authors: M
authors: M
authors: Hahn
authors: Jet Propulsion Laboratory, Caltech, Pasadena, California 91109, USA.
authors: S W
authors: SW
authors: Asmar
authors: Université de la Polynésie Francaise, Faaa, Tahiti.
authors: J-P
authors: JP
authors: Barriot
authors: Rheinisches Institut für Umweltforschung an der Universität zu Köln, Abteilung Planetenforschung, 50931 Köln, Germany.
authors: M K
authors: MK
authors: Bird
authors: Institut für Raumfahrttechnik und Weltraumnutzung, Universität der Bundeswehr München, 85577 Neubiberg, Germany.
authors: B
authors: B
authors: Häusler
authors: Rheinisches Institut für Umweltforschung an der Universität zu Köln, Abteilung Planetenforschung, 50931 Köln, Germany.
authors: K
authors: K
authors: Peter
authors: Rheinisches Institut für Umweltforschung an der Universität zu Köln, Abteilung Planetenforschung, 50931 Köln, Germany.
authors: S
authors: S
authors: Tellmann
authors: Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany.
authors: E
authors: E
authors: Grün
authors: Planetary Science Institute, 1700 East Fort Lowell Suite 106, Tucson, Arizona 85719, USA.
authors: P R
authors: PR
authors: Weissman
authors: Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany.
authors: H
authors: H
authors: Sierks
authors: Laboratoire d'Astrophysique de Marseille, 13388 Marseille, France.
authors: L
authors: L
authors: Jorda
authors: Planetary Science Institute, 1700 East Fort Lowell Suite 106, Tucson, Arizona 85719, USA.
authors: R
authors: R
authors: Gaskell
authors: Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR) Berlin-Adlershof, 12489 Berlin, Germany.
authors: F
authors: F
authors: Preusker
authors: Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR) Berlin-Adlershof, 12489 Berlin, Germany.
authors: F
authors: F
authors: Scholten