Venus has an extremely dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen, and traces of other gases including sulfur dioxide.
The mass of its atmosphere is 93 times that of Earth's, whereas the pressure at its surface is about 92 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 km (⁵⁄₈ mi) under Earth's oceans.
The density at the surface is 65 kg/m³, 6.5% that of water or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level.
The CO
2-rich atmosphere generates the strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F).
This makes Venus' surface hotter than Mercury's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F), even though Venus is nearly twice Mercury's distance from the Sun and thus receives only 25% of Mercury's solar irradiance.
This temperature is higher than that used for sterilization.

Venus' atmosphere is extremely enriched of primordial noble gases compared to that of Earth.
This enrichment indicates an early divergence from Earth in evolution.
An unusually large comet impact or accretion of a more massive primary atmosphere from solar nebula have been proposed to explain the enrichment.
However, the atmosphere is also depleted of radiogenic argon, a proxy to mantle degassing, suggesting an early shutdown of major magmatism.

Studies have suggested that billions of years ago, Venus' atmosphere could have been much more like the one surrounding Earth, and that there may have been substantial quantities of liquid water on the surface, but after a period of 600 million to several billion years, a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.
Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there is speculation on the possibility that life exists in the  upper cloud layers of Venus, 50 km (30 mi) up from the surface, where the temperature ranges between 303 and 353 K (30 and 80 °C; 86 and 176 °F) but the environment is acidic.

Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus' surface does not vary significantly between the planet's two hemispheres, those facing and not facing the Sun, despite Venus' extremely slow rotation.
Winds at the surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface.
This alone would make it difficult for a human to walk through, even without the heat, pressure, and lack of oxygen.

Above the dense CO
2 layer are thick clouds consisting mainly of sulfuric acid, which is formed by sulfur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate.
Additionally, the atmosphere consists of approximately 1% ferric chloride.
Other possible constituents of the cloud particles are ferric sulfate, aluminium chloride and phosphoric anhydride.
Clouds at different levels have different compositions and particle size distributions.
These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of Venus' surface.
The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground.
Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days.
Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed.

The surface of Venus is effectively isothermal; it retains a constant temperature not only between the two hemispheres but between the equator and the poles.
Venus' minute axial tilt—less than 3°, compared to 23° on Earth—also minimises seasona
Venus has an extremely dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen, and traces of other gases including sulfur dioxide. The mass of its atmosphere is 93 times that of Earth's, whereas the pressure at its surface is about 92 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 km (⁵⁄₈ mi) under Earth's oceans. The density at the surface is 65 kg/m³, 6.5% that of water or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. The CO
2-rich atmosphere generates the strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F). This makes Venus' surface hotter than Mercury's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F), even though Venus is nearly twice Mercury's distance from the Sun and thus receives only 25% of Mercury's solar irradiance. This temperature is higher than that used for sterilization.
Venus' atmosphere is extremely enriched of primordial noble gases compared to that of Earth. This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact or accretion of a more massive primary atmosphere from solar nebula have been proposed to explain the enrichment. However, the atmosphere is also depleted of radiogenic argon, a proxy to mantle degassing, suggesting an early shutdown of major magmatism.
Studies have suggested that billions of years ago, Venus' atmosphere could have been much more like the one surrounding Earth, and that there may have been substantial quantities of liquid water on the surface, but after a period of 600 million to several billion years, a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere. Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there is speculation on the possibility that life exists in the  upper cloud layers of Venus, 50 km (30 mi) up from the surface, where the temperature ranges between 303 and 353 K (30 and 80 °C; 86 and 176 °F) but the environment is acidic.
Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus' surface does not vary significantly between the planet's two hemispheres, those facing and not facing the Sun, despite Venus' extremely slow rotation. Winds at the surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even without the heat, pressure, and lack of oxygen.
Above the dense CO
2 layer are thick clouds consisting mainly of sulfuric acid, which is formed by sulfur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the atmosphere consists of approximately 1% ferric chloride. Other possible constituents of the cloud particles are ferric sulfate, aluminium chloride and phosphoric anhydride. Clouds at different levels have different compositions and particle size distributions. These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of Venus' surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground. Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days. Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed.
The surface of Venus is effectively isothermal; it retains a constant temperature not only between the two hemispheres but between the equator and the poles. Venus' minute axial tilt—less than 3°, compared to 23° on Earth—also minimises seasona
Venus