Beyond the orbits of Neptune and Pluto is a huge, widely spread area of mainly icy objects, from some comets come: the Kuiper Belt. In June 2002 the discovery of a 'tenth planet', Quaoar, was announced by Caltech in Pasadena. It is in fact the largest Kuiper Belt Object currently known, and is about half as big as Pluto, and about a billion miles further away,

Some Kuiper Belt Objects have their own satellites, or are 'binaries'. Here we see such a pair, and beyond them the very distant Sun, with its band of Zodiacal Light – dust and debris left behind from the formation of the Solar System, and in the plane of the planets' orbits.

Much further away even than the Kuiper Belt is the Oort Cloud. Not just a belt, this is a spherical cloud of icy bodies which are the source of long-period comets – ie those which take more than 200 years to orbit the Sun. It extends for about 3 light-years. They are only weakly affected by the Sun's gravity, and can be perturbed by other stars, sometimes making them fall towards our part of the Solar System. When they approach the Sun they begin to grow a tail.

All of the above images were used in The Sky at Night on BBC TV in April 2005.

The February 2006 issue of Sky & Telescope magazine (USA) contains an excellent review by Paul Weissman of what we have learned about comets since Fred Whipple suggested his 'dirty snowball' theory in 1950. Hardy was commissioned to produce the cover for this issue (right), as well as a double-page interior for the article.

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