Scientists do not actively ensure that there are exactly eight planets in the solar system. The number of planets in the solar system is determined by the criteria set by the International Astronomical Union (IAU), which is the internationally recognized authority for naming celestial objects and defining their classification.
In 2006, the IAU established three criteria for an object to be classified as a planet:
- The object must be in orbit around the Sun.
- The object must be spherical or nearly spherical in shape.
- The object must have cleared its orbit of other debris.
Under these criteria, Pluto, which had been considered the ninth planet, was reclassified as a "dwarf planet" because it did not meet the third criterion. It was found to share its orbit with other objects in the Kuiper Belt.
Since then, the solar system has consisted of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These are the objects that meet the IAU's criteria for planet classification.
It's important to note that our understanding of the solar system and its objects continues to evolve as new discoveries are made. Future observations and research may lead to further refinements or adjustments in our understanding of planetary classification.