The Size Distribution of Jupiter-Family Comet Nuclei

We present an updated size distribution for the nuclei of Jupiter-Family Comets, based on observations of nuclei at large heliocentric distances. The data set used includes our own recently published work and that of others published since the comprehensive review by Lamy et al. (2004, in Comets II), in addition to older measurements from the refereed literature that were included in that compilation. We apply a new approach to make a rigorous assessment of the uncertainty on the size distribution power law slope, taking into account all unknown factors and sources of uncertainty. We include: 1) the uncertainty on the original photometry; 2) the difference between the measured effective radius from snap-shot observations and the mean effective radius for observations at unknown rotational phase of a nucleus with unknown pole orientation and axial ratio; 3) the unknown solar phase function; and 4) the unknown albedo. We use a Monte Carlo technique to look at how the size distribution changes when allowing individual size measurements to vary within these uncertainties. We find the cumulative size distribution can be fit by a power law, N( > r) r^{-a}, where r is the radius and the slope, a = 1.86 ± 0.15. This work was funded in part by the NASA Planetary Astronomy Program and was performed in part at the Jet Propulsion Laboratory under contract with NASA.