Why Is Pluto Not a Planet

Pluto, designated as 134340 Pluto, is the second largest dwarf planet known to-date in the Solar System and the 10th largest heavenly body directly revolving around the Sun. Formerly classified as a planet, Pluto is presently believed the largest member of a distinctive population known as the Kuiper belt.

Just like other members of the belt, Pluto is chiefly composed of hard rock and ice and is considerably small: about one fifth the mass of the Earth’s Moon and 1/3rd of its volume. It follows an eccentric and relatively inclined orbit that carries it from 4.4 to 7.4 billion km from the Sun. This allows Pluto to periodically come near the Sun than Neptune.

Since its discovery in 1930 through 2006, Pluto was believed to be the Solar System’s ninth planet. By late 70s, after the discovery of minor planet 2060 Chiron toward the exterior of Solar System and the apprehension of Pluto’s very low mass, its consideration as a major planet invited reservations from different corners of the world.pluto Why Is Pluto Not a Planet

Years later, in the earlier part of 21st century, several similar objects as Pluto were traced out in the outer Solar System, particularly the scattered disc object Eris, 27% massive than Pluto. Consequently, the International Astronomical Union (IAU) had to redefine the term “planet” on August 24, 2006.

The new definition ommitted Pluto from the category of Planet, and included it as a member of “dwarf planet” category. As per new classification, Pluto has been assigned the number 134340. Some scientists still maintain that the status of Pluto as planet should have been unchanged.

The debate pertaining to the controversy whether Pluto is a planet or something else finally culminated in an IAU resolution, during the year 2006, which issued an official definition of the “planet”. The resolution espoused following three prerequisites for a heavenly body to qualify for a planet: -

  1. The object must orbit the sun;
  2. The object must have enough magnitude of mass that could qualify it being a sphere of its own gravitational force, i.e. its own gravitational force should form it into hydrostatic equilibrium;
  3. It will have its surrounding cleared in or around the length of its orbit.

Pluto does not meet the 3rd postulate because its mass is just 7/100 of the mass of other objects in its orbit. For example, the Earth’s mass is 1.7 million times the total mass in its revolve ways. IAU further suggested that Pluto be categorized into “dwarf planets”. Moreover, it should be held as the prototype for the ‘Plutoid’ of ‘transneptunian’ objects where it would be classified as per its concurrently learnt status.

Even the actual lunar status of Pluto’s moon Charon is dubious for the barycentre is not being traced in the centre of either body. IAU is predicting that both Pluto and Charon instead form binary system.

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