A scientist at the Open University in Britain believes he knows what makes long-period comets, such as the recent visitor, Comet Hale Bopp, come streaking into our part of the solar system. There may be a 10th planet beyond Pluto, a giant with at least as much mass as Jupiter. Dr John Murray noted that the long period comets all tended to come to the inner solar system along a single arc. He theorises that the planet's huge magnetic field would be strong enough to knock comets off of their perches at the edge of the solar system, sending them spinning in towards the sun.