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During the 1800s, astronomers began to realize most recent discoveries were unlike the traditional planets. They shared the same [[asteroid belt|region of space]], between [[Mars]] and [[Jupiter]], and had a far smaller mass. Bodies such as [[Ceres (dwarf planet)|Ceres]], [[2 Pallas|Pallas]], and [[4 Vesta|Vesta]], which had been classed as planets for almost half a century, became classified with the new designation "[[asteroid]]." From this point, a "planet" came to be understood, in the absence of any formal definition, as any "large" body that orbited the Sun. There was no apparent need to create a set limit, as  there was a dramatic size gap between the asteroids and the planets, and the spate of new discoveries seemed to have ended after the discovery of [[Neptune]] in 1846.<ref> http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html. When Did the Asteroids Become Minor Planets? U.S. Naval Observatory  

During the 1800s, astronomers began to realize most recent discoveries were unlike the traditional planets. They shared the same [[asteroid belt|region of space]], between [[Mars]] and [[Jupiter]], and had a far smaller mass. Bodies such as [[Ceres (dwarf planet)|Ceres]], [[2 Pallas|Pallas]], and [[4 Vesta|Vesta]], which had been classed as planets for almost half a century, became classified with the new designation "[[asteroid]]." From this point, a "planet" came to be understood, in the absence of any formal definition, as any "large" body that orbited the Sun. There was no apparent need to create a set limit, as  there was a dramatic size gap between the asteroids and the planets, and the spate of new discoveries seemed to have ended after the discovery of [[Neptune]] in 1846.<ref> http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html. When Did the Asteroids Become Minor Planets? U.S. Naval Observatory  

However, in the 20th century, [[Pluto]] was discovered. After initial observations led to the belief it was larger than Earth, the recently-created [[International Astronomical Union|IAU]] accepted the object as a planet. Further monitoring found the body was actually much smaller, but, as it was still larger than all known asteroids and seemingly did not exist within a larger population, it kept its status for some seventy years.<ref>{{cite web

However, in the 20th century, [[Pluto]] was discovered. After initial observations led to the belief it was larger than Earth, the recently-created [[International Astronomical Union|IAU]] accepted the object as a planet. Further monitoring found the body was actually much smaller, but, as it was still larger than all known asteroids and seemingly did not exist within a larger population, it kept its status for some seventy years. http://www.cfa.harvard.edu/icq/ICQPluto.html. Is Pluto a giant comet?

http://www.cfa.harvard.edu/icq/ICQPluto.html. Is Pluto a giant comet?

In the 1990s and early 2000s, there was a flood of discoveries of similar objects in the [[Kuiper belt|same region]] of the Solar System. Like Ceres and the asteroids before it, Pluto was found to be just one small body in a population of thousands. A growing number of astronomers argued for it to be declassified as a planet, since many similar objects approaching its size were found. The discovery of [[Eris (dwarf planet)|Eris]], a more massive object widely publicised as the [[tenth planet]], brought things to a head. The IAU set about creating the [[definition of planet]], and eventually produced one in 2006. The number of planets dropped to the eight significantly larger bodies that had [[clearing the neighbourhood|cleared their orbit]] ([[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]] & [[Neptune]]), and a new class of [[dwarf planet]]s was created, initially containing three objects (Ceres, Pluto and Eris).http://www.cfa.harvard.edu/iau/special/08747.pdf

In the 1990s and early 2000s, there was a flood of discoveries of similar objects in the [[Kuiper belt|same region]] of the Solar System. Like Ceres and the asteroids before it, Pluto was found to be just one small body in a population of thousands. A growing number of astronomers argued for it to be declassified as a planet, since many similar objects approaching its size were found. The discovery of [[Eris (dwarf planet)|Eris]], a more massive object widely publicised as the [[tenth planet]], brought things to a head. The IAU set about creating the [[definition of planet]], and eventually produced one in 2006. The number of planets dropped to the eight significantly larger bodies that had [[clearing the neighbourhood|cleared their orbit]] ([[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]] & [[Neptune]]), and a new class of [[dwarf planet]]s was created, initially containing three objects (Ceres, Pluto and Eris).http://www.cfa.harvard.edu/iau/special/08747.pdf