Atmosphere of Venus

The Atmosphere of Venus

Venus’s atmosphere has been probed by American and Russian spacecraft, theoretical calculation, and Earth based telescopes to yield many pictures. The dense clouds that obscure the surface do not reach to the ground, but end several tens miles above it. The atmosphere above the clouds consists of simple molecules – mostly carbon monoxide – while inside the clouds more complex molecules, such as sulfuric acid, may have formed. Below the clouds in a region of increasing density, temperature and pressure, the major component of the atmosphere appears to be carbon dioxide.

Venus

Craterlike shapes show on the radar image (blue) of a 900 mile section of Venus’ surface. Shown in shades and dark is the amount of radar power returned to Earth by the Venus surface. On the radar altimetry map (orange), shaded contours show a raised crater rim. The largest craters in the scene are about 100 miles in diameter, but only about 0,3 miles deep. Below is a rendition of the surface as it might appear if Venus’ clouds allowed us to see it.

Venus Landscape

Venus landscape

Venus appears to have a trough extending nearly the length of the radar image (900 miles) and measuring 75 miles wide. It is shallow – about one mile deep – and shows evidence of branching at the south (bottom) and possible “tributaries” at the northern end. The feature is interesting because it is not really a groove, but rather a crack at the top of a bulge in the surface of the planet:

Planet Venus

Below: with the atmosphere removed, you might expect a trough as shown. Artwork by Victor Costanzo:

Venus Landscape

Venus radar images present a complex puzzle to the scientist attempting to understand the nature of the planet’s surface. Familiarity of the geology of Earth, the Moon, Mercury and Mars, as well as an understanding of how geologic processes may differ in different planetary environments, is necessary before a realistic interpretation of such images can be attempted. Further complicated interpretation is the number of radar artifacts, such as the dark lane up the middle of each image, blurring near the dark lane, and the strange appearance the radar image lends to the planetary surface detail. Dr. Michael Malin of the Jet Propulsion Laboratory has given the interpretations below. Radar imagery are provided by doctor Richard Goldstein, Jet Propulsion Laboratory.

Picture of Venus

Rough mountains appear in the upper quarter of this image separated from a smooth plain by a nearly straight line indicating the possible presence of a fault. A linear feature located slightly left and above center, pointing north, may be another fault. At the approximate center of the lower half of the image lies what seems to be a cluster of mountains containing perhaps a dozen peaks in a region some 200 miles across. The individual peaks stand about one mile above the plain. This is suggestive of a region of volcanic activity.

Atmosphere of Venus, color photo

In the complex and confusing imagery of this frame several features can be deduced after careful analysis. The rough blotchy area in the right of the image is a plateau, raised about 6/10 of a mile above the bright area to the left. A thin, dark and light line appears to separate this region from areas to the left, and may be as escarpment (cliff). Altimetry data confirms that the ground is lower to the left of this feature. The bright spot in the lower right is the image of a mountainside that happened to be tipped directly toward Earth on the day this image was obtained. The average slope of the mountainside – about six degrees – can be determined from this reflection.

Greater slops may exist at higher resolution. Not very obvious is a feature located halfway between the mountain and the image center – canyon-like winding feature appearing as a depression on the altimetry data. Very little more can be distinguished until higher resolution radar images can be obtained.

Prominent in this image is the large, round, crater-like feature in the lower half of the frame. Analysis of the image reveals it to be a summit caldera atop a volcanic pile some 350 miles across. Several lines of evidence favor the caldera interpretation: 1) it has a steep inner slope and a shallow outer slope; 2) It has multiple scarps only along one side (impact craters tend to be symmetrical); 3) The large protruding ridge to the right is typical of volcanic features, and 4) the ration of its interior and exterior diameters is typical of calderas, but not impact craters. The volcanic pile can be distinguished by its texture – somewhat rougher than the surrounding terrain.

(Atmosphere of Venus) Photos: Jet Propulsion Laboratory