Found in 1930, Pluto is the ninth planet in our solar system. Unlike other stars, Pluto was found because of the disturbance it caused to Neptune's orbit. And when found, designated as a planet. However, after decades of further examination, its size has turned out to be quite small for a planet and has been reclassified. There are many reasons for this.

Firstly, let's review the difference between a planet and a dwarf star. A planet, on one hand, is in orbit of a star but is not a satellite and it has sufficient mass to be nearly spherical in shape and has cleared the neighborhood around its orbit. On the other hand, though, a dwarf planet, or in this case, Pluto, is defined as a celestial body with much the same definition as a planet but hasn't cleared its own debris field, proving that its mass is insufficient to pull all of the nearby surrounding objects into itself, absorbing them and turning into a larger star.