The concept of there being eight planets in the solar system is not something that scientists enforce or ensure. The number of planets in our solar system, specifically eight, is based on the definition set forth by the International Astronomical Union (IAU) in 2006.
According to the IAU's definition, a planet is a celestial body that meets three criteria:
- It orbits the Sun.
- It is spherical in shape, meaning it has enough mass for gravity to pull it into a roughly round shape.
- It has cleared its orbit, meaning it has become gravitationally dominant in its immediate vicinity, clearing away or controlling other objects in its orbital path.
Based on these criteria, the eight planets in our solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Before 2006, there was some debate and uncertainty about how to classify certain celestial bodies, such as Pluto. In 1930, Pluto was classified as the ninth planet, but subsequent discoveries led to questions about its status. In 2006, the IAU redefined the term "planet," and as a result, Pluto was reclassified as a "dwarf planet" since it did not meet the third criterion of clearing its orbit.
It's worth noting that the number of planets in a solar system is not a fixed rule across the universe. Other star systems may have more or fewer planets, and the definition and classification of planets can vary depending on the context and criteria used by different scientific organizations.