Why is Venus hotter than Mercury, even though Mercury is closer to the sun?
Venus's thick carbon dioxide atmosphere traps heat in an extreme greenhouse effect, while Mercury has almost no atmosphere to hold onto any warmth at all.
Quick Answer
Mercury sits closer to the sun, but it has essentially no atmosphere, so heat radiates back into space almost as fast as it arrives — its surface swings from scorching by day to hundreds of degrees below freezing at night. Venus, despite being farther out, is wrapped in a thick atmosphere that is mostly carbon dioxide. Sunlight passes through and heats the surface, but that thick atmosphere traps the heat from escaping, an extreme version of the greenhouse effect. The result is a surface temperature around 464°C (867°F), hot enough to melt lead, and hotter than any other planet in the solar system.
Key Facts
- Mercury's surface swing
- Roughly 430°C by day to -180°C at night, with virtually no atmosphere
- Venus's atmosphere
- Mostly carbon dioxide, trapping heat in an extreme greenhouse effect
- Venus's surface temperature
- About 464°C (867°F) — hot enough to melt lead
Distance from the sun isn't the whole story
How hot a planet gets depends not just on distance from the sun but on whether it has an atmosphere that can hold onto heat. Mercury is closest to the sun, but with no real atmosphere, incoming heat escapes back into space almost as quickly as it arrives.
Venus traps heat instead of releasing it
Sunlight passes through Venus's thick clouds and warms its surface, but the dense carbon-dioxide atmosphere prevents that heat from radiating back out. That trapped energy keeps building up, an extreme version of the same greenhouse effect that warms Earth on a much smaller scale.
The result: the hottest planet isn't the closest one
Venus's surface stays hot enough to melt lead around the clock, day or night, pole or equator, because its atmosphere holds the heat in so effectively. Mercury, despite its proximity to the sun, cannot compete without an atmosphere to trap that energy.