By Sabine Stanley Ph.D., John Hopkins University
Venus’s atmosphere is made up of as much carbon dioxide as is the Earth’s. However, it is much denser, creates winds strong enough to flip the planet over, turns Venus into a rocky desert, and makes a burning hell out of it at 850oF. At the same time, Venus’s distance from the Sun does not explain this extreme heat. Then what does?
Venus’s atmosphere is so thick that it looks almost impenetrable. It took humans 12 spacecraft failures until one finally landed on the planet’s hot and rocky surface. Even then, the highest spacecraft record of sending back data to Earth is 127 minutes, as the extreme heat and pressure of Venus’ atmosphere crash and burn. If Venus is Earth’s twin planet, why is its atmosphere so dramatically different?
Learn more about How the Solar System Family Is Organized.
Layers of Venus’s Atmosphere
The pressure 50 kilometers above Venus’s surface is equal to the sea-level pressure on Earth, i.e., one bar. On the surface, Venus has an atmospheric pressure of 92 bars, equal to the pressure in a one-kilometer depth of an ocean on Earth.
The bottom layer of the atmosphere of Earth, the troposphere, reaches up to almost 10 kilometers above the surface. More than 75% of atmospheric Earth’s mass is concentrated in the troposphere, and temperature decreases with the height due to convection. On the other hand, Venus’s troposphere extends up to 65 kilometers, while its other layers are smaller than Earth’s. Hence, Venus’s atmosphere is in total less than Earth’s.
Venus’s troposphere is immediately followed by the mesosphere – the middle atmosphere. The final layer is the exosphere, which is too thin for gas to behave like a gas, as collisions do not occur. Venus’s exosphere is about 220 to 350 kilometers above its surface, while Earth’s is about 600 kilometers above. Nonetheless, the composition of the two similarly-high atmospheres makes them significantly different.
This is a transcript from the video series A Field Guide to the Planets. Watch it now, on Wondrium.
The Composition of Venus’s Atmosphere
The leading element in Venus’s atmosphere is carbon dioxide, while the Earth’s is nitrogen. Interestingly, the twin planets have almost the same amount of carbon dioxide in their atmospheres. However, Earth can remove it from the atmosphere and bury it in carbonate rocks, while plants absorb it and convert it into oxygen. The carbonate rocks are usually in the oceans and are recycled back to Earth through plate tectonics, to keep carbon dioxide balance on Earth.
Conversely, Venus has no plants and oceans for removing carbon dioxide; consequently, it resides in the atmosphere to create an extreme greenhouse effect. Venus also lacks plate tectonics and cannot send carbonate rocks deep into the planet. Hence, the atmosphere is the only place for carbon dioxide to go.
Learn more about Earth: How Plate Tectonics Sets Up Life.
Acid Clouds on Venus
Another element in Venus’s atmosphere is sulfur. The UV light in the atmosphere breaks up carbon dioxide into carbon monoxide and atomic oxygen. This atomic oxygen reacts with sulfur dioxide, creating sulfur trioxide. Sulfur trioxide then combines with the very little amounts of water vapor in Venus’s atmosphere and creates the sulfuric acid H2SO4.
Thus, there are sulfuric acid clouds around the planet. The acid is strong enough even to dissolve metals and stone. These horror clouds exist at heights of around 50−70 kilometers above Venus’s surface.
Learn more about Orbiting Earth: Up through the Atmosphere.
Pressure and Temperature on Venus
Carbon dioxide domination in Venus’s atmosphere creates its high pressure, and the surface temperature of about 850°F. The temperature of each planet can be estimated by its distance from the Sun and orbital characteristics. Planets re-emit the absorbed energy as infrared, i.e., heat. The temperature derived from balancing the amount of absorbed energy with the amount of re-emitted energy is known as the equilibrium temperature.
Another term to explain the temperature of a planet is the albedo, which is the planet’s capability to reflect the Sun energy. The higher the albedo, the more the Sun energy gets reflected. Venus is thoroughly covered with reflective clouds and has the highest albedo in the solar system planets. Thus, its equilibrium temperature is about 50°F, whereas the real temperature is 850°F due to the carbon dioxide dominance.
The heat reflected from Venus gets trapped in the greenhouse gasses in Venus’s atmosphere and creates the extreme heat. On Earth, the equilibrium temperature without the greenhouse effect would be about 0°F, which is not the best condition for life. The greenhouse effect has raised it to 60°F, creating the current conditions. Lead would melt on the surface of Venus, while water melts on Earth.
Common Questions About Venus’s Atmosphere
The quick answer is no. Venus’s atmosphere contains no oxygen, is made up of 96% carbon dioxide, has a pressure 92 times higher than Earth’s sea-level pressure, and is extremely hot due to its greenhouse effect. The whole planet is a desert hot enough to melt lead, and the few water molecules that may erupt from its active volcanoes join the thick atmosphere immediately as vapor.
Venus has been nicknamed the ‘Evening Star’ as it is the brightest object after Sun and Moon in the sky. The reason is Venus’s orbit and the structure of the planet. It is much closer to the Sun than Earth is, and reflects a lot of the light across the solar system. Despite all the light it reflects, Venus’s atmosphere has made it much hotter than expected.
Venus’s atmosphere is almost 100 times thicker than the Earth’s. Venus is only 28% closer to the Sun compared to Earth, and it had the same level of carbon dioxide, as did the Earth. However, Earth had the conditions to keep running and still water as liquid and create the life that absorbs a lot of the carbon dioxide. Venus, on the other hand, had no trees and water and turned into a greenhouse with a dense atmosphere.
Venus’s atmosphere is made of 96% carbon dioxide, and even though there are some H2O molecules around as well, there is no life and liquid water to absorb the CO2 and create oxygen.