Venus Is Not Earth's Closest Planet. Here's Why
For more than 15 years, several educational websites, such as The Planets and Space Dictionary, and even NASA’s official website claimed that Venus is the nearest planet to Earth on average. Some websites even published the average distance between each pair of planets and showed that Venus is the nearest planet to Earth on average. However, this is factually incorrect.
This inaccuracy stems from a simple yet wrong assumption. For years, the average distance between two planets was calculated assuming that the average distance between every point on two concentric ellipses would be the difference in their radii. This seems quite intuitive and justified on first look. However, in reality, the aforementioned difference only shows the average distance of the ellipses’ closest points.
A better method to more accurately capture distances between planets is the point-circle method which was specifically designed to find the closest planet to Earth. This method treats a planet’s position at any given time as a uniform probabilistic distribution around a circle defined by the average orbital radius. The average distance between planets is then determined using rotational symmetry. This new procedure is quite complex when compared with the traditional procedure. However, this new procedure captures the distance between planets more accurately.
Simulations of our solar system have shown that the new procedure, the point-circle method, predicts the average distance between planets within an error margin of less than 1% while the traditional approach has an error margin of up to 300%. To understand why Mercury is the closest planet (on average), we need to understand that Mercury, due to its small orbit, never goes as far away as the other planets with their bigger orbits which makes it the closest planet to all the other planets in the solar system.
Reference: Venus is not Earth’s closest neighbor. (2019). Physics Today. Published.