Mercury Is Actually Earth’s Closest Planet on Average
Mercury is Earth’s closest planet on average, and it is also the closest planet to every other planet in the solar system.
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Mercury seems like an unlikely answer when you ask which planet is closest to Earth. Venus is often taught as our nearest planetary neighbor because Venus can make the closest single approach to Earth. But that is a different question from asking which planet stays closest on average over long periods of time. Mercury wins that comparison. Mercury orbits much closer to the Sun than Earth does, so although its position changes constantly, it does not spend long stretches wandering far from Earth. Venus can swing much farther away when it moves to the opposite side of the Sun. Researchers examined planetary positions over thousands of years and found that Mercury has the smallest average separation from Earth. The same pattern extends beyond Earth: when average distance over time is used, Mercury is also the closest planet to each of the other planets in the solar system. The surprising result comes from thinking about planets as moving objects rather than fixed points in a diagram. A planet can be the closest during a particular encounter without being the closest when distances are averaged across long periods.
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