Venus and Greenhouse Effect

Overview

This lecture explains why Venus is the hottest planet in the solar system, focusing on the greenhouse effect and its impact on planetary temperatures.

Surface Temperatures of Mercury and Venus

• Mercury is extremely hot during the day (about 660°F) but cools at night.
• By distance from the Sun, Venus should be cooler than Mercury but is actually much hotter.
• Venus has an average surface temperature of about 860°F, hotter than Mercury even during Mercury’s day.
• Venus’s temperature remains constant at night and at the poles; there are no significant seasons.

Greenhouse Effect and Atmospheric Differences

• Venus is the hottest planet due to its thick atmosphere and runaway greenhouse effect.
• The greenhouse effect is not inherently bad; on Earth, it keeps the planet warm enough for life.
• A "runaway greenhouse effect" occurs when greenhouse heating spirals out of control, as on Venus.

How the Greenhouse Effect Works

• Greenhouse gases (like CO₂) allow visible and UV sunlight to reach the ground.
• The ground absorbs sunlight, heats up, and emits infrared (IR) radiation.
• Greenhouse gases absorb the IR radiation and trap heat, preventing it from escaping into space.
• On Earth, CO₂ makes up less than 1% of the atmosphere, but it's enough to keep Earth ~50–60°F warmer than without it.
• On Venus, a high concentration of CO₂ leads to extreme heat retention.

Real-Life Analogy

• A greenhouse or a parked car with closed windows heats up because glass lets visible light in but traps infrared light, mirroring the greenhouse effect.

Key Terms & Definitions

• Greenhouse Effect — The warming of a planet due to atmospheric gases trapping infrared radiation.
• Runaway Greenhouse Effect — A greenhouse effect that intensifies uncontrollably, causing extreme heating.
• Infrared (IR) Radiation — Light with longer wavelengths than visible light, emitted by warm objects.
• CO₂ (Carbon Dioxide) — A greenhouse gas that absorbs infrared radiation and contributes to atmospheric warming.

Action Items / Next Steps

• Review the process of the greenhouse effect and its differences on Earth and Venus.
• Prepare to discuss other planetary atmospheres in the next class.