2020-4-8

Thermal inertia of a pebble-pile comet 67P/Churyumov-Gerasimenko

Arakawa Sota (postdoc, NAOJ)

Abstract:

The Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided plenty of data to understand what comets are made of.
The weak tensile strength of the cometary surface materials suggests that comets are hierarchical dust aggregates 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 inertia and the diurnal skin depth of the hierarchical aggregates of pebbles.
We found that the thermal inertia of the comet 67P/Churyumov–Gerasimenko is consistent with the hierarchical aggregate of cm- or dm-sized pebbles.
In contrast, the observed temperature dependence of the thermal inertia is inconsistent with the hierarchical aggregate of mm-sized pebbles.
Our findings indicate that the icy planetesimals might have formed via accretion of cm- or dm-sized compressed dust aggregates in the solar nebula.