The planet with the highest surface temperature is Venus. Despite being second from the Sun, Venus experiences extreme greenhouse conditions due to its thick atmosphere, composed mainly of carbon dioxide, with clouds of sulfuric acid. The average surface temperature on Venus reaches about 900 degrees Fahrenheit (475 degrees Celsius), making it hotter than Mercury, which is closer to the Sun. This intense heat prevents liquid water from existing on its surface and contributes to a hostile environment that has made exploration both challenging and fascinating for scientists.