The Solar System

Planet Basics

What is a planet?

There have been many attempts to define the term “planet” over the centuries, but to date there is still no universally agreed-upon scientific definition of the term. Generally speaking, however, a planet usually refers to an object that is not a star (that is, has no nuclear fusion going on in its core); that moves in orbit around a star; and that is mostly round because its own gravitational pull has shaped it into, more or less, a sphere.


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