Why is Venus hotter than Mercury?

Why is Venus hotter than Mercury?

• A. It is closer to the Sun
• B. It rotates faster
• C. It has a thinner atmosphere
• D. Venus has a strong greenhouse effect

Answer: (D)

The key idea here is how a planet's atmosphere traps heat and shapes its surface temperature. Venus has a very thick atmosphere rich in carbon dioxide, with clouds of sulfuric acid. This long-lived blanket of gases is highly effective at absorbing infrared radiation that the planet itself radiates after being heated by sunlight. The result is heat getting trapped near the surface, causing a runaway warming that pushes temperatures up to around 465°C. Mercury, by contrast, has almost no atmosphere, so there’s nothing to trap the heat. As sunlight heats the surface, it radiates that heat back into space quickly, and the surface can cool dramatically when night falls. So even though Mercury is closer to the Sun, it doesn’t stay as hot overall as Venus because it lacks the greenhouse warming. The other factors—distance to the Sun, or the planet’s rotation rate—don’t explain the high temperatures on Venus. Venus’s thick atmosphere and strong greenhouse effect are the dominant reason it’s hotter than Mercury.

The key idea here is how a planet's atmosphere traps heat and shapes its surface temperature. Venus has a very thick atmosphere rich in carbon dioxide, with clouds of sulfuric acid. This long-lived blanket of gases is highly effective at absorbing infrared radiation that the planet itself radiates after being heated by sunlight. The result is heat getting trapped near the surface, causing a runaway warming that pushes temperatures up to around 465°C.

Mercury, by contrast, has almost no atmosphere, so there’s nothing to trap the heat. As sunlight heats the surface, it radiates that heat back into space quickly, and the surface can cool dramatically when night falls. So even though Mercury is closer to the Sun, it doesn’t stay as hot overall as Venus because it lacks the greenhouse warming.

The other factors—distance to the Sun, or the planet’s rotation rate—don’t explain the high temperatures on Venus. Venus’s thick atmosphere and strong greenhouse effect are the dominant reason it’s hotter than Mercury.