WOW! Planet 10 Round the Corner

摘要

We learnt during our school days that there are nine planets in the solar system - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, working outwards from the sun. Subsequently, however, it was discovered that there are many small, icy objects like Pluto in the region known as the Kuiper belt which starts beyond Neptune and covers up to 55 AU (i.e. 55 times further from the sun than the earth is). The International Astronomical Union took a monumental decision in 2006 to declassify Pluto as a "Dwarf Planet". Any object in the Kuiper belt is not considered as a planet any more. The number of planets in the solar system was thus reduced to eight.