Thermal Properties, Sizes, and Size Distribution of Jupiter-Family Cometary Nuclei

TL;DR

This study uses Spitzer Space Telescope data to analyze the thermal emission, sizes, and distribution of Jupiter-family comet nuclei, providing the largest radiometrically-derived dataset and insights into their physical properties and population characteristics.

Contribution

It presents new effective radii and beaming parameters for 89 comet nuclei, offering the largest compilation of such physical properties and revealing key aspects of their size distribution and thermal behavior.

Findings

Average beaming parameter is 1.03, indicating low thermal inertia.

JFC population is incomplete below 3 km radius.

Size distribution follows a power-law with slope around -1.9.

Abstract

We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 with the Spitzer Space Telescope. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We conclude the following. (a) The average beaming parameter of the JFC population is 1.03+/-0.11, consistent with unity, and indicating low thermal inertia. (b) The known JFC population is not complete even at 3 km radius, and even for comets with perihelia near ~2 AU. (c) We find that the JFC nuclear cumulative size distribution (CSD) has a power-law slope of around -1.9. (d) This power-law is close to that derived from visible-wavelength observations, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3 to 6 km. (f) Our CSD is consistent with an intrinsic distribution that lacks many sub-kilometer objects.