Dwarf planet be discovered, and the number of planets would start growing quickly if Pluto were to remain a planet. Eris (then known as ) was discovered in January 2005; it was thought to be slightly larger than Pluto, and some reports informally referred to it as the "tenth planet". As a consequence, the issue became a matter of intense debate during the IAU General Assembly in August 2006. The IAU's initial draft proposal included Charon, Eris, and Ceres in the list of planets. After many astronomers objected to this proposal, an alternative was drawn up by the Uruguayan astronomers Julio Ángel
Atmosphere of Pluto (but also changes in viewing geometry) results in appreciable changes of brightness and color of Pluto. Methane and carbon monoxide, despite their low abundance, are significant for thermal structure of the atmosphere: methane is a strong heating agent and carbon monoxide is a cooling one (although amount of this cooling is not completely clear). "New Horizons" discovered in the atmosphere of Pluto a multi-layered haze, which covers the entirety of the dwarf planet and reaches altitude over 200 km. The best images show about 20 layers of the haze. Horizontal extent of the layers is no less than 1000 km;