SHOULD PLUTO BE REINSTATED AS A PLANET?
The two sides of the emotive decision to demote Pluto from full planetary status
The official act that took planetary classification from Pluto was IAU Resolution 5A, ‘Definition of a Planet in the Solar System’, on 24 August 2006. This document states that for an object to be considered a planet must satisfy three conditions. It states:
“A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has cleared the neighbourhood around its orbit.”
Since Pluto is not massive enough to clear its orbit of debris, it fails to meet the third condition. There’s also the problem that if Pluto were to be classed as a planet then so too would many other objects in the Kuiper Belt, and the planet count in the Solar System would rise dramatically. There are some who have argued to keep Pluto as a planet for sentimental reasons: for much of its history, it has been thought of as a planet and therefore should continue to be so. Some astronomers point out that there are inconsistencies in the wording of Resolution 5A – while it is true that Pluto hasn’t cleared its orbit, neither has Earth or Jupiter. Earth orbits with 10,000 near-Earth asteroids, while 100,000 Trojan asteroids lie within Jupiter’s orbit. One could argue that both Jupiter and Earth also fail the IAU definition. Those who hold this view say that a better definition of what a planet is might be to say that any object orbiting the Sun that has a surface area greater than 1,000km can be called a planet. If this definition were to be adopted both Pluto and Eris would be classed as planets.