The dilemma over the status of the distant Pluto was resolved on Thursday with leading astronomers approving historic new guidelines under which it is no longer defined as a planet.
After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union stripped Pluto of the planetary status it has held since its discovery in 1930.
It is the first time that scientists have had a formal definition of what is — and is not — a planet. Thursday's decision by the prestigious international group spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club.
For now, membership will be restricted to the eight 'classical' planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The much-maligned Pluto doesn't make the grade.
It has been reclassed as 'dwarf planet'. The definition also lays out a third class of lesser objects that orbit the sun -- 'small solar system bodies,' a term that will apply to numerous asteroids, comets and other natural satellites.