Venus has the distinction of being the hottest planet in the solar system, and the fault lies solely with its atmosphere. What is it about the air on Venus that keeps the planet cooking?

False-colour image of cloud features seen on Venus by the Venus Monitoring Camera (VMC) on Venus Express.
False-colour image of cloud features seen on Venus by the Venus Monitoring Camera (VMC) on Venus Express.

Atmospheric makeup

The atmosphere of Venus is made up almost completely of carbon dioxide. Nitrogen exists in small doses, as do clouds of sulfuric acid. The air of Venus is so dense that the small traces of nitrogen are four times the amount found on Earth, although nitrogen makes up more than three-fourths of the terrestrial atmosphere. This composition causes a runaway greenhouse effect that heats the planet even hotter than the surface of Mercury, although Venus lies farther from the sun. When the rocky core of Venus formed, it captured much of the gas gravitationally.

In addition to warming the planet, the heavy clouds shield it, preventing visible observations of the surface and protecting it from bombardment by all but the largest meteorites.

Although Venus and Earth are similar in size, someone standing on the ground on Venus would experience air about 90 times heavier than Earth's atmosphere; pressures are similar to diving 3,000 feet beneath the ocean. Ironically, the most Earth-like atmosphere in the solar system occurs 30 to 40 miles (50 to 60 kilometers) above the surface of Venus. Both oxygen and hydrogen rise above the heavier gas layer covering the ground, and the pressures are similar to our planet.

  • Carbon dioxide: 96 percent
  • Nitrogen: 3.5 percent
  • Carbon monoxide, argon, sulfur dioxide, and water vapor: less than 1 percent

Climate and weather

Winds of about 224 mph (360 kph) keep the clouds of Venus in constant motion. Though the planet spins slowly, only once every 243 Earth days, the clouds zip around the top of the planet every four days. But wind speeds drop closer to the surface, where they only move a few miles per hour.

On Earth, seasons change based on the planet's tilt; when a hemisphere is closer to the sun, it experiences warmer regions. But on Venus, most of the sun's heat fails to make it through the thick atmosphere. As such, the planet not only doesn't experience significant temperature changes over the course of the year, it also keeps things constant from night to day.

The clouds of Venus appear to be bright white or yellow. Unlike Jupiter or Saturn, there are no discernable bands or storms visible to the naked eye.

— Nola Taylor Redd, Contributor