The Active Surface Fraction of a Comet Nucleus from Energy-Limited Sublimation

This paper examines the fraction of a comet nucleus surface that is actively sublimating. Using only published input values and transparent formulae, the calculation obtains the following headline results: solar_flux_at_1_5AU_W_m2 = 604.9; sublimation_mass_flux_kg_m2_s = 0.0002187; nucleus_surface_area_m2 = 4.9e+07. At 1.5 AU the solar flux is about 605 watts per square metre and the energy-limited sublimation flux is about 2.2 x 10^-4 kilograms per square metre per second. Inputs, formulae and limitations bearing on the fraction of a comet nucleus surface that is actively sublimating are all declared in the text, and the accompanying script reproduces the full set of numbers without reliance on unpublished material. Agreement and disagreement with independent published estimates are reported at their actual size, and the conclusions are limited to what the budget arithmetic for the icy surface of a Jupiter-family nucleus at 1.5 AU from the Sun supports.