What is a planet?

Answer 1

In 2006, the International Astronomical Union (IAU) adopted a new definition of what constitutes a "planet" in our solar system: A celestial body that orbits the sun, has sufficient mass to assume a nearly-spherical shape resulting from its own gravity, clears out debris from the neighborhood around its orbit, and is not a satellite of another planet.

There are 8 objects in our solar system that meet this criteria; the historical planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto is now classified as a dwarf planet, along with the asteroid Ceres and the Kuiper Belt objects Haumea, Makemake, and Eris.

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Note that the above would mean that a planet in a different solar system would be defined as follows: "A celestial body that orbits a star or the remnants of a star, has sufficient mass to assume a nearly-spherical shape resulting from its own gravity, clears out debris from the neighborhood around its orbit, and is not a satellite of another planet."

Answer 2

A planet is a celestial body that orbits a star, is spherical in shape due to gravity, and has cleared its orbit of other debris. In our solar system, there are eight recognized planets, including Earth, Mars, Jupiter, and Saturn.

Answer 3

A planet is a celestrial body that orbit the star