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Difficulty: MediumThe Solar System and Planets

Although Mercury is the closest planet to the Sun, Venus maintains the highest average surface temperature of any planet in the solar system. What is the primary reason for Venus's extreme surface temperature?

  1. A
    A massive gaseous envelope composed predominantly of hydrogen and helium that prevents heat from escaping
  2. A thick atmosphere composed primarily of carbon dioxide that traps solar heat through an extreme greenhouse effectAnswer
  3. C
    Intense internal radioactive decay and continuous volcanic magma flows covering the entire rocky crust
  4. D
    A low-albedo metallic surface of exposed iron and nickel that absorbs nearly all incoming solar radiation

Answer

A thick atmosphere composed primarily of carbon dioxide that traps solar heat through an extreme greenhouse effect
Venus possesses a heavy, dense atmosphere made almost entirely of carbon dioxide. While solar radiation reaches the surface, the thick CO2CO_2 layer traps the outgoing infrared thermal radiation, producing a runaway greenhouse effect that heats the planet to over 460∘C460^\circ\text{C}, making it hotter than Mercury.

Step-by-Step Solution

1
Analyze the planetary structure and atmosphere of Venus
Venus is a terrestrial planet with an extremely dense atmosphere consisting of approximately 96.5% carbon dioxide (CO2CO_2) and clouds of sulfuric acid.
Understanding atmospheric composition is essential for explaining heat retention on terrestrial worlds.
2
Evaluate the thermal mechanism responsible for planetary heating
Visible solar radiation penetrates the upper atmosphere and warms the rocky surface, which re-emits energy as infrared radiation. The dense CO2CO_2 atmosphere absorbs and re-radiates this infrared energy, preventing it from escaping into space.
This runaway greenhouse effect creates higher average temperatures (about 465∘C465^\circ\text{C} or 869∘F869^\circ\text{F}) than on Mercury, which lacks a substantial heat-trapping atmosphere.

Key Concept

Planetary Atmospheres and the Runaway Greenhouse Effect
Estimated Time:45s
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Topics

The Solar System and Planets

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