Introduction

Abstract

Natural and artificial satellites constitute an important class of the small bodies of the solar system. Satellites (from the Latin for “attendants”) was the word chosen by Kepler in 1611 to describe Galileo’s discovery of secondary planets orbiting Jupiter. Currently 63 natural planetary satellites are known to exist: Earth and Pluto have 1 each, Mars 2, Neptune 8, Jupiter 16, Uranus 17, and Saturn 18; there are good dynamical grounds for believing that more remain to be discovered. Indeed, the discovery of Caliban and Sycorax (Gladman et al. 1997), two outer moons of Uranus moving in retrograde orbits, was made within six months of the Maratea meeting. With the discovery of a moon orbiting the asteroid (243) Ida (Belton et al. 1995), only the second asteroid to have been seen close-up, we also have to consider the possibility that natural satellites of asteroids are commonplace. As well as the natural satellites there are several hundred active artificial satellites and probably several thousand inactive ones.