Why is Pluto Excluded from the Solar System

Pluto was the 9th and farthermost planet in the solar system. It’s no longer considered a planet of the solar system, instead now called a dwarf planet. It was discovered by Clyde Tombaugh.

What is a planet after all

Scientists were not clearing the air about what’s a planet and what’s not for a long time. Then International Astronomical Union (IAU) published three criteria to decide whether a celestial body is a planet or not. The three criteria were as follows:

  1. It must be orbiting around the sun.
  2. It should have enough mass for a nearly round shape or to assume hydrostatic equilibrium.
  3. It must have cleared the surrounding or neighbouring space of other objects.

But as per the criteria, Pluto wasn’t fitting the system. It had cleared the first two criteria except the last one. The third criteria meant that the object shouldn’t cross any other object’s path or orbit, which in case of Pluto didn’t happen. Because it has an orbit that crosses its nearest planet Neptune’s orbit.

Pluto, Saturn, Uranus, Neptune, Pluto  orbits compared
Orbit of Planets

 Sun at center,    Saturn as Yellow,    Uranus as Aqua    Neptune as Blue Pluto As Violet

What is a Dwarf Planet

So, now the question arises as to why Pluto was considered as a dwarf planet. To understand that, we got to first understand what a dwarf planet is. A dwarf planet is an object in space which has no influence of its own in its surrounding space, and which isn’t a satellite itself. Same goes for Pluto.

Pluto has also the most irregular orbits among all the planets. Surprisingly, it’s even smaller than our earth’s moon. It’s even believed that this planet had its origin somewhere other than the solar system in the vast space, and it got pulled by the Sun’s powerful gravity and started orbiting around it.

Unusual Fact about Pluto

Another unusual fact about this planet is that it orbits at an angle of 17 degree to the plane, whereas other planets orbit in a flat plane. Its orbit is really elliptical in shape. One of the other dwarf planets found in the solar system named, Eris, is even bigger than Pluto. So, how can it be called a planet after all?

Earth compared to Pluto
Moon, Earth and Pluto

Author: Som Abhisek.

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