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Venus: The Veiled Planet

Venus: Optical View
Image of Venus

The second nearest planet to the Sun, Venus is shrouded in a thick, highly corrosive layer of clouds made up mostly of sulfuric acid.

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A Very Different Atmosphere

Venus's atmosphere is very dense, with the pressure at the planet's surface ninety times greater than that on Earth. Comprising 95 percent carbon dioxide, small amounts of nitrogen and traces of water vapor, the atmosphere exhibits a powerful greenhouse effect. The temperature on the planet's surface reaches about 470 degrees Celsius (896 deg. Fahrenheit), high enough to melt lead.

Looking on the Bright Side

Venus's thick bands of clouds reflect much of the sunlight back out into space. Therefore, just like the moon's, only Venus's day side is visible at optical wavelengths. However, in the millimeter portion of the radio spectrum, both the day and night side are clearly observable.

In fact, the night side appears "brighter" than the day side. This is because, in contrast to the reflected light seen at optical wavelengths, a radiotelescope operating in millimeter region detects the planet's thermal radiation. The temperature (hence "brightness") measured depends on the depth of the planet's atmosphere probed. As the atmospheric pressure mounts deeper down, the temperature increases, along with the "brightness" of the emissions picked up by the telescope.

Peering Beneath the Clouds

Venus as "Seen" with the BIMA Array
Venus: BIMA array image

Illustrated here is an image of 3 millimeter "continuum" or "broadband" radiation from the planet's atmosphere.

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However, several types of molecules in Venus's atmosphere emit millimeter radiation at more specific wavelengths and can be used as tracers to probe the atmosphere. By taking advantage of the BIMA array's excellent spectroscopic resolution, researchers can measure the motions, densities, and other physical characteristics of the clouds.

Other Ways To "See" Venus

Studies in the infrared and ultraviolet wavebands combined with radio observations at millimeter wavelengths are helping planetary scientists understand the wind and temperature patterns of Venus's atmosphere at different altitudes.

Probing beneath the clouds, researchers are also studying surface emissions at other microwave frequencies. The results indicate that the surface temperature stays the same, night and day. Still other researchers are able to peer beneath the Venus's dense clouds and map its surface features with radar, beaming radio waves towards the planet, then analyzing the returning "echoes."

Venus in Ultraviolet
Venus: ultraviolet image The ultraviolet image brings the thick clouds surrounding Venus into sharp relief. Related studies indicate that the clouds travel quickly around the planet, taking only four days to circulate once. In contrast, Venus itself rotates very slowly in the opposite direction, taking 243 days to complete one revolution.

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Venus in Infrared
Venus: infrared image This infrared image of Venus shows that, in addition to emitting greater microwave energy, roughly equal amounts of heat are radiated by Venus at night than during the day, reflecting the powerful "greenhouse" effect caused by the dense, carbon dioxide-rich atmosphere.

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Venus: a Radar View
Venus: radar 
image The radar image reveals that huge plains, punctuated by large numbers of meteorite craters, cover most of Venus's surface. Separated by the plains, volcanic regions contain a very large number of sizeable volcanoes. Scientists believe that some of the volcanoes are active, spewing gases, including sulfurous compounds, into the atmosphere.

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NCSA. Last modified 11/11/95