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UV rays pierce the clouds of Venus

New data and images of Venus have revealed a clearer picture of the cloud structure, temperature, conditions and dynamics of the planet, enabling scientists to better understand the meteorology of Venus and compare it with that of its so-called twin, Earth.

Dmitri Titov, from the Max Planck Institute for Solar System Research in Germany, and colleagues present these observations in Nature this week.

Venus is shrouded by a dense cloud layer of sulfur dioxide and sulfuric acid that reflects most sunlight back into space, which creates a ‘greenhouse effect’ and hampers direct observation of the planet’s surface.

Titov and colleagues analyzed images collected by the Venus Express spacecraft, which orbited in planet in April 2006 and used ultraviolet (UV) and infrared imaging to gather the new data. When seen in UV light, the clouds of Venus are highly variable in their brightness and shapes, which indicates spatial and vertical distribution of unknown atmospheric absorbers.

Cloud and temperature patterns of Venus, which were observed in three layers, seem to be broadly symmetrical across the two hemispheres of the planet, according to the researchers.

They report that at dark, low latitudes there is substantial convective mixing that brings the ultraviolet absorbers up from depth. In the mid latitudes, the bright and uniform clouds reside in the ‘cold collar’— a ring of cold air that suppresses vertical mixing and cuts off the supply of ultraviolet absorbers from below.

In both the low and mid latitudes, Titov and colleagues found that the visible cloud top is located at a remarkably constant altitude about 72 kilometers above the surface in both the UV dark and UV bright regions. This indicates to them that the variations in brightness seem to result from compositional differences due to the colder temperature rather than changes in elevation.

Venus and Earth are often referred to as twin planets, owing to their similar in mass and density, yet their atmospheres differ vastly; this new information is another piece of the puzzle in explaining why.

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