THE TRANS-NEPTUNIAN REGION

The search for additional planets in the Solar System beyond the known planets has fascinated the human race since time immemorial. During t he second half of this century it was realized that the source of the new comets that we observe today must also be located beyond the plane t Neptune and so as time progressed, searches of the trans-Neptunian r egion were conducted more in the hope of finding proto-comets rather t han a new planet. In 1992, a body was found orbiting the Sun in the re gion beyond the Planets and, since that date the known population has grown to a total of nearly forty bodies. This review is concerned with the search for these bodies and a summary of our knowledge to date of the known members of the population.