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 22,000 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 an area of the turbulent, cloudy middle atmosphere
some 30-33 miles above the surface, 6-10 miles below the visible cloudtops. With a spatial
resolution of about 13 miles, this is the sharpest image ever obtained of the mid- level clouds of
Venus. 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. This high-resolution map
covers a 40-degree-wide sector of the Northern Hemisphere. The several irregular vertical
stripes are data dropouts. 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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