Quick – How many planets are there in the solar system? If you were born in the 20th century, the answer might be 9 on the tip of your tongue. Of course, the official answer is 8, ever since a 2006 International Astronomical Union vote removed Pluto from the lineup.
One problem was that if Pluto were allowed to continue as a planet, it would mean adding many other Pluto-like objects to the planetary roster. The group ultimately chose to keep the solar system tidy and tidy by throwing Pluto and its friends into a box marked “dwarf planets.”
Source: www.newscientist.com
