Abstract
The orientation of plasma tail rays in type-1 cometary tails is investigated by considering a solar wind interaction similar to that observed with the planet Venus. The absence of an internal magnetic field in this planet makes possible a purely ionospheric interaction similar to that expected in a cometary environment. Applying the most recent experimental and theoretical results of the flow configuration in the Venus wake, it is predicted that the cometary tail rays are preferably formed in the vicinity of the midnight plane of the comet. The suggested coplanarity of the system of tail rays renders observation difficult for comets located at high ecliptic latitudes. This is seen as providing a self-consistent explanation of the precipitous decrease observed in the detection frequency of such structures at high latitudes.
