Pluto on Thursday lost its seven-decade status as the ninth and outermost planet of the solar system, the world’s top astronomical body decided.
The decision was made at an assembly of the International Astronomical Union (IAU).
“The eight planets are Mercury, Earth, Venus, Mars, Jupiter, Saturn, Uranus and Neptune,” said the IAU resolution, passed in a raised-hands vote after what, by the discreet standards of the astronomical community, was a stormy debate. Pluto has now been redefined as a “dwarf planet”. The need to define what it takes to be a planet stems from technological advances that enable astronomers to look further into space and to measure more precisely the size of celestial bodies in our solar system. In addition to the categories of “planet” and “dwarf planet”, a third category has been created to encompass all other objects, except satellites, to be known as “small solar-system bodies”.
Pluto’s status had been contested for many years by astronomers who said that its tiny size and highly eccentric orbit precluded it from joining the other acknowledged planets. The anti-Pluto movement gained ground after the discovery of a distant object beyond Pluto’s orbit called 2003 UB313, also known unofficially as Xena. Its discoverer said UB313 was as big as Pluto and thus could lay claim to being a planet.
Pluto was discovered on February 18 1930 by an American astronomer, Clyde Tombaugh, then aged 24.Named after the god of the underworld in classical mythology, it orbits the Sun at an average distance of 5 906 380 000km, taking 247,9 Earth years to complete a single circuit.
An unmanned United States spacecraft, New Horizons, is due to fly by Pluto and the Kuiper Belt in 2015.