Tell me why Pluto is no longer a planet.
user
There are three criteria according to the International Astronomical Union (IAU) to be classified as a full-sized planet in our system:
- It is in orbit around the Sun.
- It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
- It has “cleared the neighborhood” around its orbit.
Pluto satisfied the first two, but has not cleared its neighboring region of other objects, therefore it is not a planet.
assistant
What means for a planet that has "cleared the neighborhood"?
user
In astronomy, a planet is said to have "cleared its neighborhood" when it has become the dominant gravitational force in its orbit and has removed or accumulated most of the smaller objects, such as asteroids and debris, that were previously present. This means that the planet has gravitationally cleared its orbit of most other bodies and has become the dominant body in that region of space.

A planet that has cleared its neighborhood is considered to be a "planet" in the strict definition used by astronomers, as opposed to a dwarf planet or a small body that has not cleared its orbit. Planets that have cleared their neighborhoods include Earth, Jupiter, Saturn, Uranus, and Neptune.

In our solar system, the process of clearing a neighborhood is a gradual one that occurs over billions of years, as a planet grows in size and attracts nearby objects. The time it takes for a planet to clear its orbit depends on a variety of factors, including its size, mass, and location within the solar system.
assistant