Why is Pluto Not a Planet

Pluto, named after the Roman God of the Underworld, was discovered for the first time by Clyde W. Tombaugh in 1930. Since then, rigorous studies and photographic plate comparisons have been done for about one year, which led to the designation of Pluto as a planet. That is why, many of us grew up with the textbook lessons that our solar system comprised nine planets, namely, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Of these, Pluto was the farthest and smallest planet of the solar system.

For many decades, astronomers were unsure regarding the mass of Pluto. Consequently, there was no doubt about Pluto as a planet till 1978. In that year, astronomer James Christy discovered that this small planet has a moon (known as Charon), whose diameter is predicted to be half of Pluto. But, what led to the breakthrough that Pluto is not a planet? This article throws lights on why is Pluto not a planet .

Why is Pluto Not a Planet Anymore?

It is true that Pluto is no longer a planet, but it is categorized under the dwarf planet. This is because, Pluto fails to meet the specific requirements of being a planet. A dwarf planet is defined as any spherical object that fails to clear its neighborhood around its orbit. And for an object to be called a planet, it needs to meet certain characteristic features; it should orbit the sun, should be large enough and have sufficient center of gravity to become spherical, and last but not the least, it should be a dominating body in its orbit. Though Pluto revolves around the sun, it is very small and does not clear its orbit.

The identification of Charon is like a milestone in the field of astronomy. With the discovery of Charon that orbits Pluto, astronomers succeeded in determining the actual mass of Pluto. Unlike other planets whose size is much bigger than their moons, the size of Pluto is twice that of Charon. Also, what astronomers found out is that Pluto and Charon are more or less similar to binary planets, which take approximately 6.38 days to complete one revolution around each other.

As mentioned already, the main reason for declaration of Pluto as a dwarf planet is that it does not clear its neighborhood in the orbit. Other planets have a strong gravitational force that upon interaction with small celestial bodies (comets, asteroids, etc.), they either consume them or sweep them up. In brief, planets have a cleared orbital path, which is not so in case of Pluto. The orbit of Pluto is somewhat untidy, with many other objects around its orbit. Because of this, Pluto is now relegated as a dwarf planet.

With this brief explanation, I hope you have cleared your queries regarding why is Pluto not a planet? Or why is Pluto a dwarf planet? In the latest 2006 publication, the International Astronomical Union (IAU) officially declared that our solar system has eight planets (not nine). However, it is possible to discover a large object in the solar system that qualify the definition of a planet. Also, it can still happen that Pluto gains its mass after crashing with objects and pass the planet-hood status. Until then, we have eight planets in our solar system!