If someone asks you what planet is closest to Earth, you’ll probably blurt out Venus. That’s a perfectly normal thing to say, but it’s also wrong. Numerous websites and even NASA itself say Venus is our closest planetary neighbor. A new article in Physics Today lays out a more accurate way to determine which planets are closest together. It turns out the averages are highly counterintuitive. Mercury is the closest planet to Earth -- in fact, it’s the closest planet to every other planet.