Determining which planet is closest to Earth requires an understanding of the distances between planetary orbits within the solar system. The average distances between planets can fluctuate due to their elliptical orbits. Typically, Venus is considered the closest planet to Earth. Its orbit is the nearest in proximity, making it, on average, the closest planet to Earth for much of the time.
However, an interesting perspective called the “average proximity” approach suggests that if you consider the entire orbit around the Sun, Mercury could be argued to have the closest average distance to Earth. This is because Mercury has an orbit within the innermost part of the solar system and effectively spends less time getting relatively farther away, compared to the time Venus and Mars do in their respective orbits.
Despite this, when people talk about planetary proximity relative to Earth, they often refer to times when the planets align or are at their respective closest points (inferior conjunction for Venus). At these times, Venus is indeed much closer to Earth than either Mercury or Mars, which aligns with traditional observations and teachings. Therefore, in the context of typical orbital proximity discussions, Venus is closer than Mercury or Mars, but through analytical models considering long-term averages, Mercury can be seen as staying closer over time due to its smaller orbit.