The planet closest to Earth isn’t Venus or Mars

The order of the planets’ orbits going outward from the Sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.  The orbit of Venus is a little closer to the orbit of Earth than the orbit of Mars is.

But Venus is not our closest neighbor in the Solar System.  Mercury is, most of the time.

The thing many people forgot is that the planets are in motion, and are different distances from each other at different times.  Venus is somewhat closer to the Earth than Mercury when they are both on the same side of the Sun as Earth, but much further away than Mercury when they are on the opposite side of the Sun from Earth.  The video shows how this works.

In fact, Mercury is the closest planet to all the other planets in the Solar System for this reason.

The failure to keep in mind that the planets are constantly changing position in relation to each other invalidates the background (though not the enjoyment) a lot of old-time science fiction.

Most stories with an interplanetary background assume, without spelling it out, that a space voyage from, say, Earth and Mars is like an ocean voyage from Nantucket to Shanghai, a journey between two fixed points.

Instead, how long it would take to get from Planet A to Planet B, and how much trouble it would take, would depend on the date.


Venus is not Earth’s closest neighbor by Tom Stockman, Gabriel Monroe and Samuel Cordner for Physics Today.

[7/15/2019]  Minor edits for clarification.

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