Major Developments Major Developments by Calendar Year

August 24, 2006, was an important day in the history of planetary science. It was absolutely the first day when official scientific definition of the word “planet” is explained. It was also the famous day as Pluto was propelled out of the planetary family. Pluto is a tiny, solid, icy world in a more lengthened orbit unlike other planets, which move closely in circular paths. Another abnormality about Pluto is the inclination of its orbit. All the other planets follow paths in a confined band within the limits of the constellations, we call the zodiac, but Pluto’s orbit deviates from this and takes the path above and below that band. Another deviation is Pluto does not dominate its neighborhood i.e., Charon, its large “moon,” is only about half the size of Pluto, while all the true planets are far bigger than their moons. So officially, Pluto is not a planet and considered as dwarf planet. Pluto is the second-largest known dwarf planet in the Solar System (after Eris) and the tenth-largest body noticed, directly revolving around the Sun. Before 2006, there were nine planets, they Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Now, there are only eight planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.