The adjective planetary has to do with any astronomical body that revolves around a star — including the earth. Rather than a circle, planetary motion takes us in an elliptical shape around the sun.
In science, planetary usually describes the attributes or motion of planets. It's also used for anything that behaves in a similar way, like planetary electrons, which revolve around their atomic nucleus as if they were tiny planets. You can also talk about things that affect our entire planet using this word: "She worries a lot about the planetary effects of climate change."
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