Thermal inertias of pebble-pile comet 67P/Churyumov-Gerasimenko

Abstract

The Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided new data to better understand what comets are made of. The weak tensile strength of the cometary surface materials suggests that the comet is a hierarchical dust aggregate formed through gravitational collapse of a bound clump of small dust aggregates so-called ``pebbles'' in the gaseous solar nebula. Since pebbles are the building blocks of comets, which are the survivors of planetesimals in the solar nebula, estimating the size of pebbles using a combination of thermal observations and numerical calculations is of great importance to understand the planet formation in the outer solar system. In this study, we calculated the thermal inertias and thermal skin depths of the hierarchical aggregates of pebbles, for both diurnal and orbital variations of the temperature. We found that the thermal inertias of the comet 67P/Churyumov-Gerasimenko are consistent with the hierarchical aggregate of cm- to dm-sized pebbles. Our findings indicate that the icy planetesimals may have formed via accretion of cm- to dm-sized pebbles in the solar nebula.

17 pages, 14 figures. Accepted for publication in MNRAS

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• Survivability of Amorphous Ice in Comets Depends on the Latent Heat of Crystallization of Impure Water Ice
• Low rock mass fraction within trans-Neptunian objects inferred from the spin-orbit evolution of Orcus-Vanth and Salacia-Actaea
• Interpebble contact radius in a comet nucleus
• Oxygen Isotope Exchange Between Dust Aggregates and Ambient Nebular Gas
• Numerical Investigation on the Compressive Behavior of Hierarchical Granular Piles
• Fine-grained rim formation via kinetic dust aggregation in shock waves around evaporating icy planetesimals