Venus is hotter than Mercury because its incredibly thick carbon-dioxide atmosphere creates a runaway greenhouse effect that traps heat, while Mercury has almost no atmosphere and cannot hold on to its warmth.

Quick Scoop

  • Mercury is closer to the Sun, but has almost no atmosphere, so it heats up in the day and then cools dramatically at night.
  • Venus is farther out, yet wrapped in an ultra-dense CO₂ atmosphere over 90 times thicker than Earth’s, which acts like a thermal blanket.
  • Sunlight gets in, the surface radiates heat, but the thick CO₂ and clouds of sulfuric acid trap that heat, driving a runaway greenhouse effect.
  • Result: Venus stays around 460–470°C (about 860–875°F) almost everywhere, day and night, making it the hottest planet in the solar system.

A bit more detail

On Mercury, there’s no substantial air to insulate the planet, so surface temperatures swing from extremely hot on the dayside to extremely cold on the nightside; the heat can radiate away directly into space. Venus, by contrast, keeps its heat because its dense CO₂ atmosphere absorbs infrared radiation and circulates it efficiently around the globe, smoothing out temperatures between day and night. Over time, this turned into a runaway greenhouse effect, where trapped heat just keeps building, making Venus a permanent pressure-cooker world rather than just a hot, sunlit rock like Mercury.

Information gathered from public forums or data available on the internet and portrayed here.