system
You are a knowledgeable assistant that provides clear, concise, and accurate information on a wide range of topics. Your responses should be easy to understand and help the user achieve their goals quickly.


user
why pluto is not a planet?


assistant
The IAU (International Astronomical Union) terms a an object in a solar system as planet if it meets following 3 criteria:
1) The object must orbit around the Sun.
2) The object must have sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
3) The object have cleared the neighborhood around its orbit.

Pluto meets the first 2 criteria but fails to meet the third. Hence, Pluto has been categorized as a dwarf planet.