While many people consider Venus to be Earth’s nearest planetary neighbor, a recent commentary in Physics Today suggests that Mercury is, in fact, Earth’s closest planet on average over time. This assertion was made by Tom Stockman, Gabriel Monroe, and Samuel Cordner in a 2019 article.
Venus is often cited as our closest neighbor due to its proximity during its closest approach to Earth, which can be about 38 million kilometers when it passes between Earth and the Sun. Additionally, Venus is similar in size to Earth, making the label understandable when “closest” refers to its nearest approach.
NASA materials have also referred to Venus as our closest planetary neighbor based on this measure of closest approach.
The debate arises from the method used to calculate average distances between planets. A common method subtracts the average distances of each planet from the Sun, yielding a smaller number for Earth and Venus, which appears to indicate Venus as the closest on average.
However, this method assumes the planets are on the same side of the Sun, which is rarely the case. Stockman and the authors introduced two alternative methods: a point-circle method that averages distances across all possible orbit positions and a simulation tracking the planets’ positions over 10,000 years. The simulation showed that Mercury was the closest planet to Earth about 47% of the time, Venus 36%, and Mars 17%.
The calculation also revealed that Mercury is, on average, the closest planet to every other planet in the solar system. This is due to Mercury’s tight orbit around the Sun, which keeps it consistently near other planets compared to those on wider orbits that spend significant time on the far side of the Sun.
This finding does not alter the order of the planets or imply that Mercury comes physically closer to Earth than Venus does at its nearest approach. Venus remains the record-holder for closest approach to Earth.
The conclusion of the study addresses a specific question regarding which planet is nearest on an average distance basis over time. The ongoing debate centers around the definition of “closest neighbor” rather than the mathematical calculations, which seem to be sound.
For practical applications, particularly in spacecraft planning, the important factors are the geometry at launch and the close approaches that create transfer windows. By these measures, Venus and Mars continue to be the primary targets.
The findings present an interesting trivia point rather than redefining our understanding of the solar system.
Source: spacedaily.com via Google News.
