The Sky at Night season 22 episode 9
The Edge of the Solar System
The outer planets, Uranus, Neptune and Pluto, are now visible in the evening sky. Do these worlds mark the real edge of the Solar System? There have been suggestions that an undiscovered planet may exist and searches have been made periodically. Patrick Moore discusses the evidence, and speculates upon the possibility that our planetary system may extend much farther than is generally believed.