Scientists use a set of criteria known as the International Astronomical Union (IAU) definition of a planet to determine whether an object is classified as a planet or not. The criteria include:

    1. The object must be in orbit around the Sun.
    2. The object must have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape (this is known as hydrostatic equilibrium).
    3. The object must have cleared the neighborhood around its orbit of other debris, such as asteroids or comets.

If an object meets all three of these criteria, it is classified as a planet. If it meets the first two criteria but not the third, it is classified as a dwarf planet, like Pluto.

The third criterion is often the most controversial, as it requires that a planet must be gravitationally dominant in its orbit, meaning it has cleared out any debris that might compete with it for space in its orbit. This is why Pluto was reclassified as a dwarf planet in 2006, as it orbits in a region of the Solar System with other large objects and has not cleared its orbit of debris.

It's important to note that this definition is not without controversy and has been debated by scientists and astronomers. However, it remains the official definition used by the IAU for the classification of planets.
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