Someone (7th Feb) asked about comets.  Think homoeopathic lasers with the solar system as your body and the comets hiting minute but incredibly important fine tuning points.  Most of the random ones get sucked up by Jupiter.  Triggers, those that get through.  I've only got the barest basic functions of this site as yet, so give me a week or three........    thanks for all the lovely comments!  Leave a name!