Hottest Planets in the Solar System

Data

💡 Note: What Decides a Planet's Temperature?

When people think of the "hottest planet," most guess Mercury because it sits closest to the Sun. But the real answer is Venus, roasting at 464 °C — hot enough to melt lead (which melts at 327 °C) and even zinc (420 °C). A planet's temperature is decided by four things: distance from its star, the atmosphere it holds, how much light it reflects (albedo), and the heat it generates inside. Venus is the perfect demonstration of why distance alone doesn't decide the winner.

Why is Venus the hottest?

• Runaway greenhouse effect. Venus is wrapped in a crushing 92-bar atmosphere made almost entirely of carbon dioxide, with thick clouds of sulfuric acid.
• Those clouds and gases trap the Sun's heat far more effectively than Earth's thin CO₂ blanket — nearly all of it stays trapped, so the surface never cools off.
• The surface is so hostile that the Venera Soviet landers survived there for barely one to two hours before being crushed and cooked — Venera 13 lasted about 127 minutes while recording 464 °C at 92 bar.
• Day and night barely matter on Venus: the thick atmosphere and slow rotation (a Venusian day is longer than its year) spread the heat evenly, so the dark side stays just as hot.

Mercury: extreme swings, but a cooler average

• Mercury has almost no atmosphere, so its surface temperature swings violently — from roughly −173 °C on the night side to +427 °C on the Sun-facing side.
• Because it has nothing to trap heat, the admitted "mean" surface temperature lands around 167 °C, far below Venus.
• Interesting quirk: the closest planet to the Sun can still get colder than 0 °C in shadowed polar craters, which may hide water ice.

What "surface" means on the giants

• The gas giants (Jupiter, Saturn) and ice giants (Uranus, Neptune) have no solid surface — they are mostly hydrogen, helium, and icy compounds under enormous pressure.
• So astronomers measure their temperature at the 1-bar level, roughly the altitude where atmospheric pressure matches Earth's at sea level — that's where the visible cloud tops sit.
• These depths are genuinely freezing: Jupiter −108 °C, Saturn −139 °C, and the ice giants below −195 °C.

Fun facts about planetary cold and heat

• Uranus is the coldest planet, not the most distant one. Its atmosphere has dipped to about −224 °C, because it radiates little internal heat — the odd one out among the giants.
• Neptune, despite being farther out, is warmer than Uranus because it still releases internal heat left over from its formation (it radiates about 2.6 times more energy than it receives from the Sun).
• Earth's mean temperature of about 15 °C is a Goldilocks result: close enough to the Sun for liquid water, not so close that water boils away. Swap Earth into Venus' orbit and both oceans would boil.
• The hottest place ever recorded on Earth is Furnace Creek in Death Valley, USA: 56.7 °C in 1913. That is comfortably warm to us — yet still 400 °C colder than a typical day on Venus.
• Temperature scales mix Celsius and Kelvin in astronomy. Absolute zero is −273.15 °C, and a simple conversion is K = °C + 273.15. So Venus at 464 °C is 737 K, and Neptune at −201 °C is just 72 K.
• NASA's Parker Solar Probe is the record-holder for a human-made object's speed and proximity to the Sun, and its heat shield withstands about 1,400 °C — yet the spacecraft simply flies through the Sun's diffuse corona rather than landing on anything as hot as Venus' surface.
• Albedo matters in reverse: Venus' dazzling white clouds reflect about 70% of the sunlight that reaches it. Even so, the tiny fraction that gets absorbed is trapped so efficiently that the surface still cooks.

So the takeaway is a satisfying plot twist of planetary science: the second planet outrunks the first, one planet in the habitable zone stays pleasantly warm, and the ice giants are among the coldest places in the Solar System — all because temperature is about atmospheres and greenhouse blankets, not just how close you are to the Sun.