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The Venus Greenhouse Theory
• The absence of water in Venus' lower atmosphere spells difficulty for the "greenhouse" explanation of that planet's high temperature.
A new finding by University of California (Berkeley) scientists throws further doubt on the "greenhouse" or "runaway greenhouse" explanation of Venus' high temperature. After an intensive microwave study of Venus, Janssen, et al., (Science, March 9, 1972) reported that they could detect no water in the planet's atmosphere, and their measurements set an upper limit of two parts per thousand in the lower atmosphere. They concluded that there is not enough water to produce dense clouds, and "it remains to be shown that a 'greenhouse' mechanism can be supported with the present constraints on the water vapor content."
R. Wildt in 1940 was among the first to suggest (Ap. J., 91, 266) that the greenhouse effect might produce a relatively hot Venus—he predicted a temperature as high as 135°C. However, his views were not widely accepted. When in 1950 (Worlds in Collision, Doubleday, p. 370) Velikovsky contended that Venus' apparently contradictory properties could be explained if the planet were extremely hot and radiated heat, his opponents amassed arguments to prove that Venus is only slightly, if at all, warmer than the Earth.
In 1952 Kuiper (The Atmosphere of the Earth and Planets, 2nd ed., 1952, p. 372), using more recent data than Wildt, recalculated the greenhouse effect. He found that Venus' temperature is probably about 77°C.
By the late 1950's and early 1960's measurements revealed that Venus' temperature probably exceeded 400°C. Since the greenhouse effect alone could not account for such heat, an "enhanced" (C. Sagan, Astrophysical Journal, 65, 1960, 352) and "runaway" (S. I. Rasool, C. DeBergh, Nature, 226, 1970, 1037) greenhouse effect were proposed, with the help of hypothetical water vapor. Never fully accepted by many investigators, this view receives a substantial blow from the California scientists' findings.
In Worlds in Collision, Velikovsky had pointed out that the ancients saw Venus as an incandescent globe 3500 years ago. If this were true, he reasoned, Venus could not yet have lost its primordial heat and must be extremely hot. He also cited preliminary evidence (Pensée, May, 1972, 51) pointing toward a cooling process on Venus—a matter which should be investigated further. If such cooling should be solidly proven, it is difficult to imagine what further excuses could prevent investigators from considering Velikovsky's explanation for Venus' heat.
Venus, it seems, is not finished posing mysteries for Earthlings. A team of scientists at Caltech's Jet Propulsion Laboratory report (Astrophysical Journal, 181: L5-L8, April 1, 1973) a study of the strength of carbon dioxide absorptions in Venus' spectrum. Having discovered a 20 percent variation over a four-day period, they ask, "What is happening on Venus?"
Their answer: "To produce the observed changes in line length, the cloud tops must be moving up and down by 0.2 scale height, or over one kilometer, all over the disk at once. A large amount of energy is required to drive such large-scale changes, and it is difficult to see where it can come from on a slowly rotating planet with low and spatially uniform absorption of solar radiation. We seem to be observing a fundamental feature of the atmospheric dynamics that is not explained by current theories of atmospheric circulation on Venus."
PENSEE Journal V