(4. Juni 1976)

If the magnetic field in a type I comet tail were of internal origin, it would decrease with distance along the tail axis, and the comet tail would increase in cross section. The tail of Comet Arend-Roland (1957 III) was shown not to expand with distance from the nucleus, whence it is concluded that the magnetic field in the tail is of external origin. The magnetic field in type I comet tails, estimated from different considerations, turns out to be of the order of the interplanetary field, so that one may suppose that it results from the captured solar-wind magnetic field.

Recently, Mendis and Alfvén (1974) suggested that substantial magnetic fields, up to 100-1000y, could sometimes be generated within the coma. This means that the magnetic field in the comet tail may result from processes analogous to those producing the Earth‘s magnetotail.