Is Mercury the hottest planet?

No.Venus is the hottest planet in our solar system, at about 872°F (467°C) on the surface, even though Mercury is closer to the Sun. Venus's thick atmosphere traps heat; Mercury has almost no atmosphere to keep it.

What's actually true

Venus, not Mercury, is the hottest planet. Mercury is closest to the Sun, so it seems like the obvious winner. But Venus is hotter, with surface temperatures around 872°F (467°C). Its thick carbon dioxide atmosphere traps heat, so the surface stays scorching day and night. Mercury has almost no atmosphere to hold heat, so its night side gets very cold.

Takeaway: Venus is the hottest planet, about 872°F, because its thick atmosphere traps heat. Being closest to the Sun isn't enough.

Why people believe it

Distance from the Sun is the rule we learn first, and for most planets it works: the farther out, the colder. Mercury is closest, so it seems it must be hottest. The missing piece is the atmosphere. A thick blanket of carbon dioxide turns Venus into a runaway greenhouse, while Mercury lets its heat escape into space, so its night side drops far below freezing.

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