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Thick air, hot planet
Age 14 · Physics
A planet’s atmosphere lets sunlight in but slows the heat trying to leave, so a thicker atmosphere leaves the surface hotter. Venus has a very thick one and is scorching, Earth’s is just right for life, and Mars’s is so thin that it stays freezing.
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In the picture
- Venus’s thick atmosphere: it traps almost all outgoing heat
- Earth’s thin atmosphere: it lets some heat escape and keeps some
- Mars’s faint atmosphere: most heat slips away into space
- Heat sent back down: this is the greenhouse effect warming the surface
Examples
- A car parked in the sun gets hot inside because its glass lets light in but keeps the heat from escaping.
- A cloudy night stays warmer than a clear one because clouds send heat back down.
Key takeaways
- The thicker the atmosphere, the more heat it traps and the hotter the surface.
- Venus is hotter than Mercury even though it is farther from the Sun.
Quiz: Thick air, hot planet (Age 14)
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Why does Mars stay freezing cold?
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Venus is farther from the Sun than Mercury, yet it is hotter. Why?
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What does the greenhouse effect do to a planet’s surface?
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