The first visit to another planet

On this day in 1962, a spacecraft called Mariner 2 flew past Venus, the first spacecraft ever to fly past another planet and send back what it found. It measured how hot Venus is and studied the space around it.

Why it mattered

Mariner 2 found that Venus is very hot, much hotter than the Earth, because its thick air holds in the sun's heat like a heavy blanket.