Venus is the closest planet to Earth, right? Yes and no. To identify our closest neighbor, engineers affiliated with NASA, Los Alamos National Observatory, and the US Army's Engineer Research Development Center built a computer simulation to calculate the average proximity of Earth to its three nearest planets (Mars, Venus, and Mercury) over a 10,000-year-period. Because of the way the planets align during their respective orbits, the model shows that Earth spends more time nearer to Mercury than either Venus or Mars. “In other words, Mercury is closer to Earth, on average, than Venus is because it orbits the Sun more closely,” the authors explain. It’s not just Earth. Further calculations suggest that all seven planets in the Solar System spend most of their orbit closer to Mercury than any other planet. Sounds impossible? This is how they worked it out. The results are based on a technique called the point-circle method (PCM) – in essence, a mathematical equation that takes the orbits of two planets as circular, concentric, and coplanar, and calculates the average distance between two planets as they orbit the sun. "From the PCM, we noticed that the distance between two orbiting bodies is at a minimum when the inner orbit is at a minimum," the authors explain. "That observation results in what we call the whirly-dirly corollary (named after an episode of the cartoon Rick and Morty): For two bodies with roughly coplanar, concentric, circular orbits, the average distance between the two bodies decreases as the radius of the inner orbit decreases." "It’s clear from this corollary, and from the table, that Mercury (average orbital radius of 0.39 AU), not Venus (average radius of 0.72 AU), is the closest planet to Earth on average." (AU is astronomical units, the distance between Earth and the Sun.) Running a simulation that tracked the positions of all four planets over a 10,000-year-period and calculated the average distance between them, they found this to be true for all the other planets in the solar system. Mercury is always the closest. Credit: @tomstockman
