Which Planet Is the Hottest in the Solar System?
Which planet is the hottest in the solar system? Most people say Mercury. It makes sense, it sits closest to the Sun. Spoiler: wrong. The hottest planet is Venus, and it's not even close. Its surface sits at around 464°C (867°F), hot enough to melt lead. Mercury doesn't come near it. So how can a planet almost twice as far from the Sun be much hotter? The answer is its atmosphere. We'll show you why Venus breaks every record and why your gut gets this one wrong.
Which planet is the hottest, and how hot exactly?
The hottest planet in the solar system is Venus. Its average surface temperature is around 464°C (867°F). That heat is the same everywhere, day or night, pole or equator. For context: lead melts at 327°C (621°F). On Venus, you'd be liquid in no time.
Why Mercury is not the hottest planet
Here's where it gets strange. Mercury sits closest to the Sun, about 36 million miles (58 million km) away. Venus is almost twice as far, around 67 million miles (108 million km). Yet Venus is far hotter. Why?
Because Mercury has almost no atmosphere. In the daytime its surface hits 800°F (430°C). At night it drops to around minus 290°F (minus 180°C). With no air to hold the heat, it escapes straight into space. On average Mercury sits at just 167°C.
Did you know?
On Mercury, daytime temperatures can hit 800°F (430°C) and night temperatures fall to minus 290°F (minus 180°C). That's a swing of more than 1,000°F, all because the planet has no atmosphere to trap heat.
A greenhouse effect that ran away
Venus does the opposite. Its atmosphere is 96.5% carbon dioxide. The pressure at the surface is about 92 times Earth's. That's like being 3,000 feet (900 m) underwater.
This thick blanket acts like a trap. Sunlight comes in and heats the ground. The heat tries to leave, but the atmosphere won't let it out. It stays locked in. Scientists call this a runaway greenhouse effect. That's exactly why they study Venus as a warning sign for Earth.
Want to test your gut for numbers like these? Try our science estimation questions. Free, runs right in your browser.
A day on Venus is longer than a year
Here's one more fact that ties your brain in a knot. Venus spins so slowly that a single rotation takes about 243 Earth days. Its trip around the Sun, its year, takes only about 225 Earth days. So a day on Venus is longer than its year. And it spins backwards, so the Sun would rise in the west.
Which planet is the hottest in the solar system?▾
Venus. Its surface averages around 464°C (867°F). That beats Mercury, even though Mercury sits closer to the Sun. The heat on Venus is the same everywhere, day or night.
Why is Venus hotter than Mercury if Mercury is closer to the Sun?▾
Because Venus has a dense carbon dioxide atmosphere that traps heat like a blanket. Mercury has almost no atmosphere, so it loses its heat straight into space the moment the Sun goes down.
How hot is it on Venus?▾
Around 464°C (867°F) on average, hot enough to melt lead. The temperature stays nearly the same across the whole planet, from pole to equator and day to night.
How hot and how cold does Mercury get?▾
Mercury reaches up to 800°F (430°C) during the day. At night it falls to around minus 290°F (minus 180°C). That's a swing of more than 1,000°F because it has no atmosphere to hold the heat.
What is the atmosphere of Venus made of?▾
About 96.5% carbon dioxide. The surface pressure is roughly 92 times Earth's, similar to the pressure 3,000 feet (900 m) underwater.
Is a day on Venus really longer than a year?▾
Yes. One full rotation of Venus takes about 243 Earth days. One orbit around the Sun, its year, takes only about 225 Earth days. So a Venus day is longer than a Venus year.
Remember this: distance from the Sun doesn't decide the heat on its own. The atmosphere does. That's why Venus, at 464°C, is the hottest planet, not Sun-hugging Mercury. If you like surprises like this, read how hot the Sun really is, or how far the Moon really is.
Autor:in
Leon EikmeierChefredakteur
Leon Eikmeier ist Gründer von Quiztimate und MetaOne. Er schreibt über kontraintuitive Fakten, Wissen und die Psychologie des Lernens.