These images are two versions of a near-infrared map of lower- level clouds on the night side of
Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it
approached the planet February 10, 1990. Taken from an altitude of about 60,000 miles above the
planet, at an infrared wavelength of 2.3 microns (about three times the longest wavelength
visible to the human eye) the map shows the turbulent, cloudy middle atmosphere some 30-33
miles above the surface, 6-10 miles below the visible cloudtops. The image to the left shows the
radiant heat from the lower atmosphere (about 400 degrees Fahrenheit) shining through the
sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between
clouds. This cloud layer is at about -30 degrees Fahrenheit, at a pressure about 1/2 Earth's
atmospheric pressure. About 2/3 of the dark hemisphere is visible, centered on longitude 350
West, with bright slivers of daylit high clouds visible at top and bottom left. The right image, a
modified negative, represents what scientists believe would be the visual appearance of this
mid-level cloud deck in daylight, with the clouds reflecting sunlight instead of blocking out
infrared from the hot planet and lower atmosphere. Near the equator, the clouds appear fluffy and
blocky; farther north, they are stretched out into East-West filaments by winds estimated at
more than 150 mph, while the poles are capped by thick clouds at this altitude. The Near Infrared
Mapping Spectrometer (NIMS) on the Galileo spacecraft is a combined mapping (imaging) and
spectral instrument. It can sense 408 contiguous wavelengths from 0.7 microns (deep red) to 5.2
microns, and can construct a map or image by mechanical scanning. It can spectroscopically
analyze atmospheres and surfaces and construct thermal and chemical maps. Designed and
operated by scientists and engineers at the Jet Propulsion Laboratory, NIMS involves 15
scientists in the U.S., England, and France. The Galileo Project is managed for NASA's Office of
Space Science and Applications by JPL; its mission is to study the planet Jupiter and its
satellites and magnetosphere after multiple gravity-assist flybys at Venus and the Earth.
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