National Geographic : 1963 May
Scanning Venus three times, Mariner's nodding instruments probed night side, sunrise line, and finally the day side. They reported solid clouds that produce a "greenhouse effect," blanketing the surface in a heat of 800° F. (below). vital earth sensor became meaningless-it was so hot the reading was "off the dial." Now neither optimists nor pessimists would have any figures to base their hopes or worries on. The night of December 13, 1962, was cru cial. At that time Mariner was supposed to turn on the two radiometers, by a command stored in its electronic brain. About 50 per sons manned the control room, quiet and tense, at 11:21 p.m., waiting for the signal. None came. Battery temperature had reached 129° F. Earth sensor temperature: unknown. Mariner would again be in position to turn on its instruments by itself at 2:40 a.m. Every one waited. Again nothing happened. There was one more chance. The experi ments might be turned on from earth through the Goldstone antenna. Venus would "rise" over Goldstone at 4:16 a.m. Everyone waited. Goldstone tracked Mariner for half an hour to make sure of its aim, then gave the order. Mariner was so far away from earth that the radio command, traveling at the speed of 742 light, took more than 6 minutes to reach the craft and return. When the coded answer flashed back, it reported that Mariner had obeyed. And so, after 6 minutes and 30 sec onds of utter quiet, the control room exploded with laughter and clapping. Now, if only the solar heat didn't wreck something, success seemed sure. And, at 10 seconds before 1 p.m. on December 14, 1962, a still-vocal Mariner reached its closest point to Venus-21,700 miles-and sent its infor mation 36 million miles back to its creators. Venus - Searing, Dry, and Gloomy After months of study, Mariner scientists reported to the world. Their findings, with other experiments, round out a fascinating picture of our nearest neighbor planet. The atmosphere is hostile to man, rich in carbon dioxide, poor in water vapor and oxy gen. Continuous cloud cover-15 to 20 miles thick and starting 45 miles above the surface -creates a "greenhouse effect," letting sun energy reach the planet, but preventing much of the heat from escaping into space. Though astronomers had assigned a tem perature of 600° to the surface, Mariner raised this estimate 200°. The searing surface is ap parently dry and granular, perhaps sandy. Over it, slow winds circulate dense gases. Compressed in an atmosphere 10 to 20 times heavier than ours, the gases readily conduct heat around the planet. This explains why Mariner found no temperature difference be tween sunlit and dark sides. The clouds keep Venus gloomy as well as hot. Apparently made up of hydrocarbons, they might be called smog. Mariner's instruments found no planetary magnetic field at 21,700 miles from Venus, nor did they locate any bands of radiation like earth's Van Allen belt. The absence of such bands agrees with other observations that indicate a very slow-perhaps nonexist ent-rotation of the planet. To an observer on Venus, if it does not rotate, the stars would seem to stand still, while the sun, rising in the west and setting in the east, would circle the planet in 225 days, the period of Venus's solar orbit. Thus Venus's day would equal its year. As Mariner soars on in silent orbit around the sun, NASA's Dr. Homer E. Newell sums up the craft's verdict on an age-old question: "With the surface of Venus hot enough to melt lead, the planet cannot support life as we know it." But biologists, he adds, reserve judgment on whether lower forms of life might exist in the planet's upper atmosphere. "Investigation of that," the scientist con cludes, "will have to wait until we get there."