Why is Pluto no longer considered a planet?

Pluto was reclassified from a planet to a dwarf planet primarily because it does not meet all the criteria defined by the International Astronomical Union (IAU) in 2006 for an object to be considered a full-fledged planet. According to the IAU, for a celestial body to be classified as a planet, it must satisfy three conditions: 1. It must orbit the Sun. 2. It must be massive enough for its gravity to shape it into a nearly round (hydrostatic equilibrium) shape. 3. It must have "cleared the neighborhood" around its orbit, meaning it is gravitationally dominant and has removed smaller objects and debris near its orbital path. Pluto meets the first two criteria: it orbits the Sun and is spherical in shape. However, Pluto fails the third criterion because it shares its orbital zone with other objects in the Kuiper Belt, a region of the Solar System beyond Neptune filled with many small icy bodies. Pluto's gravitational influence is not strong enough to clear these nearby objects, so it cannot be considered dominant in its orbital neighborhood. Because of this, the IAU introduced the category of "dwarf planet" for bodies like Pluto that meet the first two criteria but not the third. This reclassification helps astronomers better categorize the diverse objects in our Solar System based on their physical and orbital characteristics.