The interaction of rotation and magnetic field in the Solar system

During the early phases of star formation, torsional Alfven waves propagating along the locally distorted galactic magnetic field can transport away the bulk of the initial angular momentum of a condensation, so enabling it to contract to solar nebula dimensions. Enough primeval magnetic flux may be retained for magnetic redistribution of angular momentum to continue until the proto-sun reaches the pre-Main Sequence Hayashi phase. A rotating star with a convective envelope has a dynamo-maintained field which brakes the star through coupling to the stellar wind. Observational evidence from young star clusters and from T Tauri stars suggests that the zero-age Main Sequence Sun had about ten times its present angular momentum. The same braking process, scaled up because of the much more powerful T Tauri winds, can explain why the zero-age sun had lost at least nine-tenths of the centrifugal upper limit, and is more acceptable than the suggestion that the 'missing' solar angular momentum has been magnetically fed into the planetary system. (author)