Introduction

Abstract

The study of asteroids started on the first day of the 19th century when Piazzi, observing from Palermo, discovered a new object in the Solar System. Though the specific discovery by Piazzi was serendipidous, a campaign had been initiated by von Zach, whereby the zodiac was divided into 24 zones and a different astronomer was assigned to search each zone for a suspected planet. Piazzi was not one of these 24 astronomers. The expectation of finding a planet was based on the belief that the Titius-Bode law that predicted planetary distances was correct (see Nieto 1973 for a discussion of this law). We must remember that its correctness had only recently in 1781 been demonstrated through the discovery of the planet Uranus by Herschel. The only unexpected element in the discovery by Piazzi was that the new planet, named Ceres, was rather faint, much fainter than expected, indicating that the body was somewhat smaller than the “predicted” planet. Within the next four years, three further similar objects were discovered, Pallas, Juno and Vesta, two by Olbers and Juno by Harding. No further objects of this class were discovered for 40 years and it was during this period that the group were called minor planets — for they clearly were not proper planets. It was also during this time interval that the hypothesis was put forward first that these minor planets were remnants of a proper planet that had been broken up by some mechanism.