What Is Venus's Atmosphere Like?
QUICK ANSWER
Venus's atmosphere is the densest of any rocky planet, composed mostly of carbon dioxide (96.5 percent), with surface pressure 92 times Earth's, sulfuric acid clouds, and almost no water. The thick atmosphere is what causes Venus's runaway greenhouse effect and uniformly extreme surface temperatures.
Venus's atmosphere is what makes Venus hellish. The surface conditions, the lethal temperatures, the crushing pressure, the chemistry of the clouds, all come down to what's in the air. Understanding Venus is largely a matter of understanding what's wrapped around it.
What is Venus's atmosphere made of?
According to NASA, Venus's atmosphere is about 96.5 percent carbon dioxide, 3.5 percent nitrogen, and trace amounts of sulfur dioxide, water vapor, carbon monoxide, and other gases. Earth's atmosphere by comparison is 78 percent nitrogen and 21 percent oxygen, with only 0.04 percent carbon dioxide. Venus's atmosphere essentially has the same gases Earth's does, just in radically different proportions, with CO2 dominant instead of trace.
How thick is Venus's atmosphere?
Extremely. Surface atmospheric pressure on Venus is about 92 bars, which is 92 times the pressure at Earth's sea level. To put that in perspective, you'd have to dive about 3,000 feet underwater on Earth to feel the same pressure. Venus's atmosphere is so thick that the air itself behaves almost like a fluid near the surface, dense enough that walking through it would feel more like walking through water than air. Spacecraft visiting Venus have to be built more like submarines than like aircraft.
What are Venus's clouds made of?
Venus's clouds are made primarily of droplets of sulfuric acid, with some hydrochloric acid mixed in. The cloud layer sits between about 30 and 45 miles above the surface and is thick enough to completely hide the ground from view in visible light. Acid rain falls from the clouds, but the temperature increases rapidly as you descend, so the rain evaporates before it reaches the surface, never actually touching the ground. The clouds also rotate around Venus much faster than the planet itself, completing a full circuit in about 4 Earth days.
How does Venus's atmosphere drive the greenhouse effect?
Carbon dioxide is exceptionally good at absorbing infrared radiation. When sunlight reaches Venus's surface and warms it, the surface re-radiates that heat as infrared, which the CO2 atmosphere absorbs and re-emits in all directions, including back toward the surface. With so much CO2 and so much heat trapped, the surface temperature climbs to about 900°F and stays there constantly. Without the dense CO2 atmosphere, Venus would be much closer in temperature to Earth, despite being closer to the Sun.
Venus's atmosphere is the planet's defining feature: 96.5 percent carbon dioxide, 92 times Earth's pressure, laced with sulfuric acid clouds, and responsible for the runaway greenhouse effect that makes the surface uninhabitable. Understand Venus's atmosphere and you understand the planet. It's the engine that drives everything else about Venus.
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