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Why is Pluto Not a Planet?

Why Is Pluto Not a Planet? Everything You need to Know

From its discovery in 1930 to its declassification in 2006, Pluto was considered to be one of the planets in the solar system. However, at a Prague conference in 2006, this all changed. Instead of being a planet, Pluto was moved to the newly created category of “dwarf planet”. Why was this change made, and what exactly makes Pluto so different? Why is Pluto not a planet?


why pluto is not a planet

What Is A Planet?

The word planet is derived from the Greek word “planetes”. It refers to a celestial object that orbits a star, is big enough to have enough gravity to take a spherical shape, and is big enough that any other similar objects around it would be cleared. This definition came into use in 2006 under the authority of the International Astronomical Union.

Planets have been chartered and categorized since the Ancient Greek societies, although the definitions for what was a planet were very different, with both the moon and sun also being called planetary bodies. It was finally agreed in the 17th century that all planets rotated around the sun, and at a similar time, it was also decided that the moon was in fact not a planet. It was instead classified as a satellite of Earth.

Our current solar system is known to have the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Now to answer the question “why is Pluto not a planet”, we need to look at its history and characteristics.

why is pluto is not a planet

Pluto’s History As A Planet

Pluto was discovered in the year 1930 by a man called Clyde Tombaugh, and at the time it was considered to be a planet. It is extremely small – its diameter is only 2/of the size of Earth’s moon. It is small and rocky, and its mass is only 2/10 of 1% of Earth.

Its orbit is very different from the other planets in the solar system – instead of being a roughly circular orbit, Pluto has an elongated oval-shaped orbit instead. This became one of the reasons why Pluto was declassified as a planet in 2006.

why is pluto no longer a planet

So Why Is Pluto Not A Planet?

Pluto is separated from the rest of the planets in the solar system due to the definitions outlined in 2006 of a planet and a dwarf planet. While a planet is a celestial object that orbits a star, big enough to have enough gravity to take a spherical shape, and is big enough that any other similar objects around it would be cleared, a dwarf planet orbits the sun, has enough mass to assume a shape that is nearly round, is not a moon, and has not cleared the neighborhood around its orbit.

Pluto fits the fourth criteria for being a dwarf planet. It also has a completely different orbital path to the other planets, setting it apart from them. It is not necessarily Pluto’s size or mass that stops it from being classified as a planet, it is its unusual orbit (although still traveling around the sun) and the fact that it does not have the necessary gravitational pull to clear the neighborhood around its orbit that leads it to be considered a dwarf planet instead.


Overall, there are various factors that led to Pluto being categorized as a dwarf planet in 2006. Despite being taught to be a planet since its discovery in 1930, it was eventually recognized to have too unique of an orbit and to have not cleared enough of its neighboring debris to reach planetary status.

If you want to read more about – why is Pluto not a planet, you can read here.

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