Venus is a star.
Venus . It has the densest atmosphere of the four terrestrial planets , consisting of more than 96 % carbon dioxide . Venus was the first planet to have its motions plotted across the sky , as early as the second millennium BC . As the closest planet to Earth , Venus has been a prime target for early interplanetary exploration . It was the first planet beyond Earth visited by a spacecraft ( Mariner 2 in 1962 ) , and the first to be successfully landed on ( by Venera 7 in 1970 ) .