Postulate:
All Comets are originated as “Small Comets”, by Birkeland magnetic field interference near to the solar surface as is shown in the photograph. http://migratingblackholes.blogspot.com/
mentioned before.
All these Comets where able to produce or gather enough water molecules, during their journey away from the sun, to be influenced by the solar gravity field and become an elliptical orbit around the sun.