Pluto....Planet Exiled

Upto now, all science textbooks and other Astronomy related books describe our Solar System as having the Sun at the center, nine planets revolving around the Sun, several small and big satellites of the planets and other objects like asteroids and comets.

Finally the time has come which indicates that a change is needed in the description of the Solar System. The smallest planet of the Solar System, Pluto, has now been revoked of its status as a planet. This makes our solar system comprised of eight planets, instead of nine.

Pluto is not the only planet, which is revoked of its status. In 1801, a small rocky body was discovered which was later named as Ceres was proclaimed as a planet. A year later a second rocky body was found in a similar orbit; several other discoveries along the same lines soon followed. In 1802 Ceres's planet hood was also revoked.

Ever since the discovery of  (former planet) Pluto in 1930, scientists always had differing views of whether it should at all be considered as a planet. The main reason for changing Pluto's status is its' own size. It is so small that it cannot even compete with a few of the natural satellites of other planets, for e.g. Jupiter's Ganymede, Saturn's Titan, and Earth's Moon are bigger than Pluto. Of course, for that matter even Mercury is smaller than Ganymede, but it is denser and has a near circular orbit around the Sun, whereas while orbiting around the Sun, Pluto cuts through the Neptune's orbit making it the ninth planet. Pluto being small in size and less dense has low gravitational force, which doesn't help much in keeping its path along the orbit clear of debris.

The IAU (International Astronomical Union) decided to lay clear the rules and criteria for an object to be called as a planet. The rules are as follows:

1. An object that is in orbit around the Sun

2. An object that has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes hydrostatic equilibrium (nearly round) shape

3. An object that has cleared the neighborhood around its orbit

Pluto satisfies the first and the second rule but fails to comply with the third one and that throws it out of the planetary status. IAU also defined a set of rules for an object to be considered as a Dwarf Planet and the rules are as follows:

1. An object that is in orbit around the Sun

2. An object that has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes hydrostatic equilibrium (nearly round) shape

3. An object that has NOT cleared the neighborhood around its orbit

4. An object that should not be a satellite of any other planet of the Solar System

Since the final stroke of Pluto's demotion, it often occurs that many brilliant scientists and experts died with knowledge that our Solar System contains nine planets, millions of teachers trained billions of students about nine planets and now there will be a drastic change. New discoveries and inventions have always compelled scientists to rethink on the established beliefs and theories. Centuries old belief about earth-centered universe was one day shattered, so was the belief of instantaneous effect of light, absolute space and absolute time. All these have changed and now we are witnessing a change in the number of planets, saying goodbye to the ninth planet.