Activity and nucleus properties of 46 P/Wirtanen

Astronomical observations of size and of related outgassing rates seem not to be compatible for the nucleus of comet 46 P/Wirtanen, the target comet o f the ROSETTA mission. This possible disagreement has caused speculations a bout peculiar properties of this comet nucleus. It is shown by model calcul ations which also takes into account vertical heat fluxes into the nucleus that there is a possibility to combine the results of astronomical observat ions within a model of a freely sublimating ice surface of this comet with an outgassing area of about half the dayside surface. The resulting 'half-s ize' parameter (i.e. the radius of an equivalent sphere) can be shown to be of about R approximate to (725 +/- 230) m, and the nucleus is shown to hav e an active area of about half of the dayside surface, i.e. of about 25% of the total surface. (C) 1999 Elsevier Science Ltd. All rights reserved.