Responses (6)
Pluto used to be classed as a planet but with the discovery of other Kuiper-belt objects and the later observation of Eris in 2005 (an object in our Solar system larger than Pluto) a decision had to be made as to whether Eris should become a planet or Pluto and similar objects should be relegated to the term Dwarf planet. In 2006 a meeting of the world's astronomers and other scientists decided that Pluto would be declassified, this decision was seen as controversial at the time but if this change had not happened there would now be between 13 and 17 planets in our Solar system. Pluto is still out there.