Planet Closest to Earth

Venus is not the planet closest to Earth on average.  At a close approach to Earth, yes, Venus is closer to our planet than any other planet and closer to Earth than the sun.

But averaging the distance from Venus to Earth over time, that average distance is greater than the average distance from Mercury to Earth.  Mercury is usually closer to Earth than Venus is.  This is a strange and counter-intuitive truth, but there it is.  Even odder is the fact that Mercury is also, on average, the closest planet to Mars and Jupiter and Saturn and Uranus and even Neptune.  Though not orbiting the Sun in the near-plane of the eight planets, Mercury is also the closest planet to Pluto on average.

Closest approach is not the same as closest distance on average.  This is a very recent discovery.  See https://physicstoday.scitation.org/do/10.1063/PT.6.3.20190312a/full/