Influence of the energy input on the vapor flux and on the temperature distribution of comet nuclei

Abstract

Understanding the power balance at the surface of the nucleus is essential to study the chemical and physical evolution of a comet. Therefore, we present a detailed energy budget analysis for the surface of a model comet in the orbit of P/Wirtanen, target comet of the European spacecraft mission Rosetta, for a variety of parameters and assumptions. We will show that for a fast spinning Jupiter-family comet like P/Wirtanen with a rotation period of about 6 hours a fast rotator approximation unterestimates the effective energy input. This yields to lower gas fluxes from the surface. For an active, not dust covered surface we obtain a water gas flux on the order of about 2 + 10_28 molecules s_-1. This value is within the order if measured values for comet P/Wirtanen at perihelion. But the calculated values are maximum gas fluxes at noon - not averaged over one cometary day or takung lesser insolation of the pol areas into account. Therefore we conclude that maybe the determined radion of comet P/Wirtanen is much larger than the value of 700 m. A radius in the order of 2 or 3 km seems to be more likely to explain the measurements. One other possibility could be that water ice particles are blown off from the surface like dust particles. This may also increase the effective surface area of sublimation.