The current definition, adopted in 2006 by the International Astronomical Union (IAU), states that a planet must:
1. Orbit the Sun.
2. Be massive enough for its own gravity to make it round.
3. Have cleared its neighborhood around its orbit.
This definition led to Pluto being reclassified as a dwarf planet because it failed to meet the third criterion. Pluto shares its orbital space with many other objects in the Kuiper belt.
However, this definition is not without controversy:
* Some argue that the third criterion is arbitrary and makes the definition unnecessarily restrictive. It's argued that other celestial bodies like Eris, Ceres, and Makemake should also be considered planets.
* Others argue that the current definition is a good one, as it helps to distinguish planets from other celestial bodies. This makes it easier to study and categorize objects in our solar system.
The debate continues, and there is no easy answer. Some scientists believe that the definition should be revisited, while others believe that it is working well as is. It's likely that the debate will continue for some time, as there is no clear consensus on the best way to define a planet.
Beyond the definition, there are also discussions about the possibility of discovering new planets in our solar system. While we haven't found any new planets in recent years, the possibility of discovering new objects, particularly beyond the orbit of Neptune, remains.
In short, the debate about the number of planets in our solar system is a complex one, involving both scientific and philosophical considerations. It's a debate that will likely continue as we learn more about our solar system and the universe beyond.
