John Moran on Pluto

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Pluto and Charon

This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope. The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 4.4 billion km from Earth.

John Moran, Planetarium operator at World Museum Liverpool, sent this summary of the recent controversy surrounding Pluto:

'In August 2006, the International Astronomical Union held a meeting in Prague. The purpose of this meeting was to decide the fate of the ninth planet in our solar system, Pluto.
In light of recent discoveries in the Kuiper belt; a huge expanse of space bodies beyond Pluto, it has been decided to de-classify Pluto to the status of "Dwarf planet", therefore eliminating it from our nine planet system.
The definition of a planet is that it must move around the Sun in a continuous non interrupted orbit. It must have enough mass for its gravity to squash it into a spherical shape. And the plain of its orbit must lay in an almost straight line, similar to the other planets. The problem with Pluto, is that its orbit crosses that of Neptune and its plain is much steeper, so therefore very different to the other planets.
It has long been known that Pluto was probably a Kuiper belt object. But with the recent discoveries of Sedna and Zena, scientists were left with a dilemma. Do we keep adding more and more KBO's to the overall number of planets in our solar system? Or do we take the unprecedented step of demoting Pluto? They decided on the latter.
This may be a controversial step, and one that will upset many people. But as one scientist put it, "we must look at the solar system as it is, not as we would like it to be".'