The categorization of planets in our solar system is based on the guidelines set by the International Astronomical Union (IAU), the internationally recognized authority responsible for classifying celestial bodies. The IAU established a formal definition of a planet in 2006, which helps differentiate between planets and other objects in the solar system.
According to the IAU's definition, a celestial body must meet the following criteria to be considered a planet:
- It must orbit the Sun.
- It must be spherical in shape, or in hydrostatic equilibrium, meaning it has enough mass for gravity to pull it into a round shape.
- It must have cleared its orbit of other debris and objects, meaning it is the dominant gravitational influence in its orbital zone.
Based on these criteria, there are currently eight recognized planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These objects fulfill the requirements outlined by the IAU's definition.
It's worth noting that the reclassification in 2006 led to the reclassification of Pluto, which was previously considered the ninth planet. Pluto, along with other similar-sized objects in its vicinity, was redefined as a "dwarf planet" since it did not meet the criterion of having cleared its orbit. This decision was made to create a more precise and consistent definition of what constitutes a planet.
While our current understanding is based on the IAU's definition, the scientific understanding of celestial objects can evolve over time as new discoveries are made. Future research and advancements in our knowledge may lead to revisions in our understanding of planetary classification.