The IAU General Assembly meets every three years. on August 24, 2006 the Assembly passed a resolution that redefined the
definition of a planet, which classified Ceres, 2003 UB313 and Pluto as dwarf planets, and reduced the number of planets in
the solar system to 8.
The details are presented below
Kuiper Belt Objects(KBOs)/Trans Neptunian Objects Due to its small size and distant location, some astronomers argue that Pluto isn't a planet at all.
They think of it as giant asteroid, or comet. If so, Pluto would then become the largest known member of the Kuiper belt, a disc full of icy bodies that swarm outside the planets.
There is a disk-shaped region called Kuiper belt, past the orbit of Neptune roughly 450 crore km to 1500 crore kms from the
Sun. It is considered to be the source of the short-period comets. Astronomers also call the objects in this belt
Trans-Neptunian objects. There are estimated to be perhaps 70,000 Trans Neptunian Objects (TNOs), each at least 100 km
across. Some astronomers for a long time kept arguing that Pluto & Charon should be considered to be large Kupier belt
As a growing area of the sky is searched for Kupier belt objects, astronomers are beginning to detect the larger objects.
They have over 1000 km diameter. The first such object discovered was Varuna, measured in 2001. Later they announced the
discovery of Quaoar, Sedna, 2003 UB313 and many more. About 10 such objects have been found so far. Of these 2003 UB313 is
suspected to be bigger than Pluto. It is at a distance of 1770 crore km from the Sun.
Pluto’s classification as a "dwarf planet"
There has recently been considerable controversy about the classification of Pluto. It was classified as the ninth planet
shortly after its discovery and remained so for 75 years. But on 2006 Aug 24 the IAU decided on a new definition of "planet"
which does not include Pluto. Pluto is now classified as a "dwarf planet", a class distict from "planet".
The International Astronomical Union (IAU) unites national astronomical societies from around the world. It is
internationally recognized by astronomers as the official authority responsible for naming stars, planets, asteroids, and
other celestial bodies and phenomena, and is the official body of astronomy.
The XXVIth General Assembly of the International Astronomical Union was held during August 14 to August 25, 2006 in Prague,
Czech Republic. The IAU General Assembly meets every three years. on August 24, 2006 the Assembly passed a resolution that
redefined the definition of a planet, which classified Ceres, 2003 UB313 and Pluto as dwarf planets, and reduced the number
of planets in the solar system to 8.
The Eight Official Planets
The 2006 redefinition of "planet" by the International Astronomical Union (IAU) states that, in the solar system, a planet is
an astronomical object if it satisfies the following conditions
1.The object must be in orbit around a star, but not be a star itself.
2.The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should
pull it into a shape of hydrostatic equilibrium.
3.It must have cleared the neighborhood around its orbit. This means nothing of comparable mass may orbit near the planet.
A non-satellite body fulfilling only the first two criteria is classified as a "dwarf planet", whilst a non-satellite body
fulfilling only the first criterion is termed a "small solar system body" (SSSB).
According to the definition, there are currently eight planets and three dwarf planets known in the solar system.
The three dwarf planets are : Pluto, Ceres and 2003 UB 213 (xena)
Ceres is a dwarf planet in the asteroid belt. Its name is derived from the Roman goddess Ceres - the goddess of growing
plants and of motherly love. It was discovered on January 1, 1801, by Giuseppe Piazzi. With a diameter of about 950 km, Ceres
is by far the largest and most massive body in the asteroid belt: it contains approximately a third of the belt's total mass.
The classification of Ceres has changed more than once. At the time of its discovery it was considered a planet, but upon the
realization that it represented the first of a class of many similar bodies, it was reclassified as an asteroid for over 150
The New Solar System with Eight Planets and Three Dwarf Planets