What is a Planet? main content.

What is a Planet?

Part of Dorothy and Lewis B. Cullman Hall of the Universe.

What is a planet_HERO AMNH/D. Finnin

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In our solar system, planets are the major bodies orbiting the Sun. Because we cannot yet observe other planetary systems in similar detail, a universal definition of a planet has not emerged. In general, planets are massive enough for their gravity to make them spherical, but small enough to avoid nuclear fusion in their cores.