The Sky at Night

The Hunt for the Tenth Planet

0.0July 19, 1982

Is there a new planet in the solar system? Many astronomers believe that there is a massive body beyond Neptune, the outermost of the main planets now known: it could be a planet, but it might also be a dark star or a black hole. The movements of the two Pioneer space-craft now on their way out of the solar system may provide valuable clues. Patrick Moore gives an up-to-date report.