At first glance, it seems obvious which planet should be the hottest: Mercury, the one closest to the Sun. But nature doesn’t always follow our assumptions.
In reality, Venus, the second planet from the Sun, is significantly hotter than Mercury—hot enough to melt lead, cook spacecraft in minutes, and erase any chance of surface water.
So… Why?
Let’s look at the key differences:
1. Atmosphere Makes All the Difference
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Mercury has almost no atmosphere. Its surface absorbs solar heat during the day, but without air to trap that heat, it escapes quickly after sunset.
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Venus, on the other hand, has a thick, toxic atmosphere made mostly of carbon dioxide (CO₂), over 90 times denser than Earth’s.
That thick atmosphere acts like a massive thermal blanket—trapping heat in a runaway greenhouse effect.
2. Temperatures Compared
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Mercury:
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Daytime: up to 430°C (800°F)
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Nighttime: as low as −180°C (−290°F)
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Huge temperature swings between day and night
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Venus:
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Surface temperature: about 465°C (870°F) day and night
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Constant heat, no cool-down period
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In fact, Venus is hotter than Mercury at all times, despite being nearly 50 million kilometers farther from the Sun.
3. Venus’ Cloudy Skies
Venus is permanently shrouded in thick sulfuric acid clouds, which reflect most sunlight. Ironically, most of the heat doesn’t come from direct sunlight—it comes from infrared radiation trapped by CO₂, bouncing again and again within the atmosphere.
What This Tells Us
The case of Venus teaches us something crucial:
Atmosphere, not distance, is what determines a planet’s temperature.
It also serves as a stark warning. Venus may once have had oceans, like Earth. But runaway greenhouse gases turned it into a hellish pressure cooker, with crushing air and acidic rain that evaporates before hitting the ground.
Venus isn’t the closest planet to the Sun—
But it’s the hottest world in the solar system.
And a haunting reminder of what happens when a planet’s climate runs out of control.
