atmosphere of Venus
Venus' atmosphere consists almost entirely (96.5%) of carbon dioxide, with clouds containing droplets of sulfuric acid along with compounds of chlorine and fluorine. These precipitate an acid rain called virga, which evaporates before it has the chance to reach the surface. In the upper part of the atmosphere, clouds swirl by at a rate of 300 km/h, driven by fierce winds.
History of observationsThat Venus was permanently enveloped in what appeared to be thick, white clouds soon became clear following the development of the telescope. By analogy with the Earth, it was generally assumed that these clouds were made of water vapor, a conclusion supported by early spectroscopic studies by Secchi. The main composition of the atmosphere remained a matter for conjecture until spectroscopic observations by Walter Adams and Theodore Dunham, in 1932, established that it was carbon dioxide. Speculation about the make-up of the clouds continued. In 1937, R. Wildt suggested methanal (formaldehyde), while in 1954, Fred Whipple and Donald Menzel proposed ice crystals. Today, they are known to consist primarily of sulfuric acid.
Hydroxyl radical in Venusian atmosphereIn the May 2008 issue of Astronomy & Astrophysics, Picconi et al. report the first detection of the hydroxyl (-OH) radical in the night-side airglow emission of Venus. The discovery was made using an instrument onboard Venus Express. This is the first detection of -OH in the atmosphere of a planet other than Earth. It is important because it will give new insight into the dynamics of the upper atmosphere and the climate system of Venus.
Cold layerAlthough the surface of Venus swelters at an average temperature of 467°C, and much of the planet's atmosphere is also hot, there is a layer within the atmosphere that is surprisingly cold – colder, in fact, than anywhere in the Earth's atmosphere. At an altitude of about 125 kilometers above the surface, measurements by the Venus Express probe have shown, the temperature drops to an amazingly low -175°C, cool enough in theory for carbon dioxide ice or snow to form.
Related entrieslife on Venus
atmosphere of Mars
Related category PLANETS AND MOONS
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