Pluto is known as a dwarf planet because of its size and characteristics. Here are the main reasons why:

Size and Shape
- Pluto is significantly smaller than the eight planets of our solar system.
- Its diameter is only about 2,377 km, which is less than one-fifth of the Earth's diameter.
- Pluto also has an irregular shape, unlike the round shape of most planets.

Orbit
- Pluto's orbit is highly elliptical and tilted compared to the other planets.
- It takes 248 Earth years for Pluto to complete one orbit around the Sun.

Composition
- Pluto is made up of rock and ice, similar to the composition of other planets in the outer solar system.
- However, it is not massive enough to clear its orbit of other debris, which is a requirement for a planet.

Classification
- In 2006, the International Astronomical Union (IAU) redefined the term "planet" and classified Pluto as a "dwarf planet."
- According to the IAU, a dwarf planet is a celestial body that orbits the Sun, has a nearly round shape, and has not cleared its orbit of debris.

In summary, Pluto's small size, irregular shape, highly elliptical orbit, and inability to clear its orbit of debris led to its classification as a dwarf planet.

Because it is smaller than all planets and it has no orbit to take revolution around The Sun