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Atmosphere of Venus

Atmosphere of Venus
Venus
Cloud structure in Venus's atmosphere in 1979,
revealed by ultraviolet observations from Pioneer Venus Orbiter
General information
Height 250 km
Average surface pressure 93 bar or 9.2 MPa
Mass 4.8 × 1020 kg
Composition
Carbon dioxide 96.5%
Nitrogen 3.5%
Sulfur dioxide 150 ppm
Argon 70 ppm
Water vapour 20 ppm
Carbon monoxide 17 ppm
Helium 12 ppm
Neon 7 ppm
Hydrogen chloride 0.1–0.6 ppm
Hydrogen fluoride 0.001–0.005 ppm

The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K (467 °C, 872 °F), and the pressure is 93 bar (9.3 MPa), roughly the pressure found 900 m (3,000 ft) underwater on Earth. The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible. Information about the topography has been obtained exclusively by radar imaging. Aside from carbon dioxide, the other main component is nitrogen. Other chemical compounds are present only in trace amounts.

Mikhail Lomonosov was the first person to hypothesize the existence of an atmosphere on Venus based on his observation of the transit of Venus of 1761 in a small observatory near his house in Saint Petersburg, Russia.

The upper atmosphere is in a state of vigorous circulation and super-rotation. The whole atmosphere circles the planet in just four Earth days, much faster than the planet's sidereal day of 243 days. The winds supporting super-rotation blow as fast as 100 m/s (~360 km/h or 220 mph). Winds move at up to 60 times the speed of the planet's rotation, while Earth's fastest winds are only 10% to 20% rotation speed. On the other hand, the wind speed becomes increasingly slower as the elevation from the surface decreases, with the breeze barely reaching the speed of 10 km/h (2.8 m/s) on the surface. Near the poles are anticyclonic structures called polar vortices. Each vortex is double-eyed and shows a characteristic S-shaped pattern of clouds.

Unlike Earth, Venus lacks a magnetic field. Its ionosphere separates the atmosphere from outer space and the solar wind. This ionised layer excludes the solar magnetic field, giving Venus a distinct magnetic environment. This is considered Venus's induced magnetosphere. Lighter gases, including water vapour, are continuously blown away by the solar wind through the induced magnetotail. It is speculated that the atmosphere of Venus up to around 4 billion years ago was more like that of the Earth with liquid water on the surface. A runaway greenhouse effect may have been caused by the evaporation of the surface water and subsequent rise of the levels of other greenhouse gases.


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