Clouds Lift on Mysterious Winds of Venus
This animation of wind circulation on Venus is composed of images taken by the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA’s Venus Express between April 2006 and June 2007. The night-side of the planet is at the top in infrared, with the day-side at the bottom.
Credit: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/ Universidad del País Vasco (R.Hueso)

Veiled Venus just got a little less mysterious in a new 3-D view that showcases the planet's powerful winds.

The European Space Agency's Venus Express spacecraft tracked cloud movements hidden within the murky depths of Venus' southern hemisphere, and scoped out the huge hurricane-like vortexes spinning over the planet's poles.

"Tracking them for long periods of time gives us a precise idea of the speed of the winds that make the clouds move and of the variation in the winds," said Agustin Sanchez-Lavega, a planetary scientist at the Universidad del Pais Vasco in Bilbao, Spain.

Sanchez-Lavega and the Venus Express team followed 625 clouds at a 41-mile altitude (66 km), 662 clouds at a roughly 38-mile altitude (61 km), and 932 clouds at altitudes of 28 to 29 miles (45 to 47 km).

An instrument called the Venus Express Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) peered at visible cloud motions at the upper altitudes during the day, and switched to the infrared range of light to see lower cloud movements at night.

The team found that the wind speed could vary from almost 230 mph (370 km/h) at the 41-mile altitude to roughly 130 mph (210 km/h) at the 28 to 29 mile altitude range. On Earth, wind speeds can regularly top 100 mph above 18,000 feet, and occasionally hit 200 mph at 30,000 feet.

Such results could help researchers begin to understand the complex weather system of Earth's neighboring planet.

"Our measurements will first help to constrain existing models of Venus General Circulation," Sanchez-Lavega told "At present, Venus General Circulation remains unexplained, representing a challenge for researchers."

Wind patterns changed drastically near the hurricane-like weather of the poles. Winds of roughly the same speed pushed clouds at all altitudes, although the speed dropped to almost zero at the center of the giant vortex.

For the first time, Venus Express also uncovered a vertical map of the zonal winds, or winds that blow parallel to the lines of latitude. The zonal wind speeds blow more strongly in the evenings on Venus because of the difference in the sun's heat, also called the solar tide effect.

The Venus Express team chose to examine the southern hemisphere because the spacecraft reaches its highest point in orbit there, at 41,000 miles (66 km) above the planet.

"At present we cannot observe the northern hemisphere with the VIRTIS instrument," Sanchez-Lavega said. "If there is a second extension of the mission, we could reach the north. With other instruments, in particular with the Venus Monitoring Camera, part of the north is available for the measurement of cloud motions."

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