Answer: Venus
Surprised? Mercury is the closest planet to our sun (at 58 million km), so why is Venus (which is 108 million km from the sun) the hottest?
Venus has an atmosphere that is mostly made up of carbon dioxide which is a green house gas. This atmosphere acts a bit like a one way open door that lets in the sun’s radiation and then retains the heat like an oven. In contrast, Mercury doesn’t have an atmosphere, so it only experiences heat when it faces the sun and when it turns its back to the sun, it loses its heat as there is not atmosphere to trap it. In fact, the surface temperature of Mercury varies from 425C when facing the sun and drops to -173C on the shadow side. But Venus, with its atmospheric trapping shell soars up to 460C.
