What is a Planet?

  • Exhibition Text

    • 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.

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  • For Educators

    • Topic: Astronomy

      Subtopic: Planets

      Keywords: Astrophysics, Planets

      Audience: General

In This Section

Our Planetary Neighborhood

Our Planetary Neighborhood

Orbiting our star, the Sun, are the inner rocky planets and the outer gas giant planets, along with their many moons.