The Dust Mantle of Comet 9P/Tempel 1: Dynamical Constraints on Physical Properties

Abstract

The trajectories of dust particles ejected from a comet are affected by solar radiation pressure as a function of their ratios of radiation pressure cross section to mass. Therefore, a study on the orbital evolution of the particles caused by the radiation pressure reveals the physical properties of dust on the surface of the comet nucleus. In the course of NASA's Deep Impact mission, the ejecta plume evolved under the influence of the radiation pressure. From the evolution and shape of the plume, we have succeeded in obtaining $\beta \approx 0.4$, where $\beta$ is the ratio of the radiation pressure to the solar gravity. Taking into account $\beta \approx 0.4$ as well as the observational constraints of a high color temperature and a small silicate-feature strength, dust particles ejected from the surface of comet 9P/Tempel 1 are likely compact dust aggregates of sizes $\approx 20\mu$m (mass $\sim 10^{-8}$\,g). This is comparable to the major dust on the surface of comet 1P/Halley ($\sim 10\mu$m) inferred from in-situ measurements and theoretical considerations. Since such dust aggregates with $\beta \approx 0.4$ must have survived on the surface against jets due to ice sublimation, the temperature of ice in the nucleus must be kept below 145\,K, which is much lower than equilibrium temperature determined by solar irradiation and thermal emission. These facts indicate that 9P/Tempel 1 has a dust mantle composed of $20\mu$m-sized dust aggregates with low thermal conductivities $\sim 1{\mathrm{erg}\mathrm{cm}}^{-1}{\mathrm{K}}^{-1}{\mathrm{s}}^{-1}$.

4 pages, 3 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (5)

• Two different evolutionary types of comets proved by polarimetric and infrared properties of their dust
• Cometary Dust Trail Associated with Rosetta Mission Target: 67P/Churyumov-Gerasimenko
• Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact
• Comet 9P/Tempel 1: Interpretation with the Deep Impact Results
• Deep Impact: Optical Spectroscopy and Photometry Obtained at MIRA

Cited by in corpus (8)

• An interferometric study of the Fomalhaut inner debris disk. III. Detailed models of the exozodiacal disk and its origin
• The tensile strength of dust aggregates consisting of small elastic grains: Constraints on the size of condensates in protoplanetary disks
• The Morphological, Elastic, and Electric Properties of Dust Aggregates in Comets: A Close Look at COSIMA/Rosetta's Data on Dust in Comet 67P/Churyumov-Gerasimenko
• Geometrical structure and thermal conductivity of dust aggregates formed via ballistic cluster-cluster aggregation
• Light Scattering and Thermal Emission by Primitive Dust Particles in Planetary Systems
• SOFIA Infrared Spectrophotometry of Comet C/2012 K1 (Pan-STARRS)
• How much large dust could be present in hot exozodiacal dust systems?
• Monitoring Observations of the Jupiter-Family Comet 17P/Holmes during 2014 Perihelion Passage