Abstract
We derive masses and densities for a number of short period comets with known sizes, including 1P/Halley, 2P/Encke, 6P/d'Arrest, 9P/Tempel 1, 10P/Tempel 2, 19P/Borrelly, 22P/Kopff, 45P/Honda-Mkros-Pajdusáková, 46P/Wirtanen, 67P/Churyumov-Gerasimenko and 81P/Wild 2. The method follows the one developed by Rickman et al. (1987) based on the asymmetry of the gas production curve, and the delay or advance in the time of the perihelion passage with respect to the one derived for a purely gravitational orbit. This delay or advance in the time of the perihelion passage is related to a change in the orbital period, which is due to the forces arising from the anisotropic outflow of gas, causing a jet acceleration on the nucleus. The gas production curve is derived from an empirical correlation with the visual light curve. Therefore, from the observed light curve and change in the orbital period, we can derive the perturbing force components and hence the mass. The computed densities are in all cases very low (less than about 0.8/cm^3) in agreement with previous results and models of the cometary nucleus depicting it as a very porous object.