The number of planets in our solar system hasn't changed. There are still eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The reason we sometimes hear about "only eight planets" is because in 2006, Pluto was reclassified as a dwarf planet.

This happened because the International Astronomical Union (IAU) defined a planet as a celestial body that:

1. Orbits the Sun.

2. Has enough gravity to pull itself into a nearly round shape.

3. Has cleared its neighborhood around its orbit.

Pluto, while meeting the first two criteria, failed the third. It shares its orbital space with other objects in the Kuiper Belt.

So, while Pluto is no longer considered a planet, it's still a fascinating and important celestial body. It's just classified differently.