Astronomers at the XXVIth General Assembly of the International Astronomical Union have voted to reclassify Pluto as a “dwarf planet” under a new classification scheme. The three types of bodies are:
- Planets: The eight worlds starting with Mercury and moving out to Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Dwarf planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite."
- Small solar system bodies: All other objects orbiting the sun.
Already this decision is under attack. Some note that neither Earth nor Jupiter has cleared the neighbourhood around their orbits. Also the resolution was voted upon by only 424 astronomers out of the world’s approximately 10,000 professional astronomers.
One reason for the decision was the 2005 discovery of 2003 UB313 nicknamed “Xena”, a trans-Neptunian object (TNO) larger than Pluto based on photographs taken in 2003. As it became likely that other objects larger than Pluto would be discovered astronomers had to decide what actually was a planet.
NASA’s New Horizons probe is reach its closest point to Pluto in 2015. If the question of Pluto’s status is still open, some of the information collection could help settle the matter.