The visual appearance of comets under varying solar wind conditions

Abstract

Three dimensional MHD simulations have been performed for four different sets of solar wind conditions and cometary outgassing rates appropriate to the Halley encounters. Even though the simulations are single fluid calculations, it is possible to separate the solar wind and cometary ions using the divergenceless nature of the solar wind ions. We then integrate the cometary ion density along the line-of-sight from the observer through the comet to determine how the comet would look to a distant observer under these different conditions. In general comet tails appear longer when the interplanetary magnetic field lies in the plane of the sky rather than along the line-of- sight. Also the tail shrinks as the speed of the solar wind increases and/or the mass loading rate decreases.