Coma Gas Number Density Profile from a Haser Description of Outgassing

This paper examines the radial number density profile of gas in a cometary coma. Using only published input values and transparent formulae, the calculation obtains the following headline results: Q_molecules_s = 1e+27; expansion_speed_m_s = 800; parent_scale_length_km = 8e+04. Density falls from about 10^15 molecules per cubic metre at ten kilometres from the centre to about 9 x 10^8 at ten thousand kilometres, a drop of more than six orders of magnitude over three decades of distance, with the exponential factor contributing noticeably only in the outermost value. For the radial number density profile of gas in a cometary coma, every input is named and every formula is stated, and the deposited script regenerates each quoted value, so the calculation can be audited or rescaled by any reader. Agreement and disagreement with independent published estimates are reported at their actual size, and the conclusions are limited to what the budget arithmetic for an expanding coma described by the classical Haser formulation supports.