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Interesting Facts about Venus's Clouds

Updated: Jun 18, 2022

By Rosalyn Brady

March 26, 2022


[Photo Credit:]

The most notable feature of the planet Venus is its layer of sulfuric acid clouds twenty kilometres thick. These clouds are located between 45-50 and 65-70 km above the surface of Venus.

These clouds were first studied in the 1960s using spectroscopy, which is observation and analysis of the light any celestial object, such as Venus, emits, and using this data to make inferences of the properties of this object, such as its mass, how bright it is, and what it is made of, and using polarimetry, which is the analysis of the direction of propagation, or the direction in which light waves travel, to develop inferences on a planet’s magnetic field - which in the case of Venus is an ‘induced magnetosphere’ caused by the interaction of solar winds with electric currents created by charged atoms in parts of Venus’ atmosphere - or other properties. This was used to infer the presence of sulphuric acid in these clouds in 1973, which was confirmed by in situ analyses - analyses in the place of origin - throughout the USSR’s Venera-12 missions in 1978, and the USA’s Pioneer Venus missions in 1979.

This sulphuric acid makes up the vast majority of Venus’ cloud composition, the rest of which is sulfur dioxide. In Venus’ upper atmosphere, carbon dioxide (CO2) is broken down by the Sun’s ultraviolet radiation in a phenomenon known as photolysis. The oxygen (O) left over from this photolysis reacts with sulfur dioxide (SO2) to form sulfur trioxide (SO3). The SO3 then reacts with water (H2O) in Venus’ atmosphere to form sulphuric acid (H2SO4), and the sulphuric acid enters a liquid state due to the pressure from the surrounding sulphuric gases. Some of these H2SO4 droplets migrate through Venus’ upward atmosphere down to the lower atmosphere at the slow speed of 1 mm/s ^-1, or 1 millimetre per second. As they descend, they decompose until they vapourize at 40 km above the surface of Venus.

Usually, since Venus’ clouds are so dense, they reflect 70% of the sunlight that shines on them; this causes Venus’ intense brightness and its high albedo - fraction of light reflected by any celestial object - of 0.7. However, Venus’ topmost cloud layer has an interesting phenomenon shown through ultraviolet light imaging: dark streaks, places in which ultraviolet light is mostly absorbed. These dark streaks stay persistent even despite the wind speeds as high as 360 kilometers (224 miles) per hour. While other stationary cloud patterns were confirmed by the Japan Space Exploration Agency’s Akatsuki orbiter to be stationary ‘Lee waves’, which are caused by winds coming into contact with high-altitude obstacles, such as mountains, it is unknown what may cause these dark streaks. It is most likely that these dark streaks are caused by things like fine particles or iron chloride dissolved in the clouds; however, atmospheric temperatures at this level range from 30C to 70C, ideal for bacteria that thrive in high temperatures, which could be protected from sulfuric acid by linked ring-shaped sulfur atoms that are confirmed to exist in Venus’ atmosphere and could provide bacteria a protective coating. It is additionally known that earlier Venera-12 missions detected elongated particles with the same length and width as a bacterium.

It may be a long while before the source of the dark streaks can be confirmed. But for now, as improbable as it is, we must wonder: could hellish Venus harbour life? And if it doesn’t today, could it tomorrow - perhaps in the form of the Venusian cloud cities which are so widely discussed as a form of interplanetary expansion?


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