Venus Is Dead, & Too Hot

Next week, if all goes well, the National Aeronautics and Space Administration will launch Mariner 5, a $30 million spacecraft designed to shoot past Venus at a distance of only 2,000 miles and probe the mysteries of the cloud-shrouded planet during its flyby. Whatever its findings, however, Mariner will hardly be able to top the recent accomplishment of astronomers in a plane flying only 37,000 feet above the earth. Using an ingenious scheme and sophisticated equipment, they determined conclusively that Venus is a bone-dry planet devoid of water--and probably devoid of any kind of life.

Even after Mariner 2 determined in 1962 that the surface temperature of Venus was about 800DEG F., some scientists expressed the hope that life might exist on its cooler mountaintops or among the water clouds and ice crystals believed to exist in the Venusian atmosphere. But the yellow hue of Venusian clouds has long caused University of Arizona Astronomer Gerard Kuiper, 61, to doubt that they were composed of water in any form.

Split Image. To test his suspicion, Kuiper loaded a team of scientists, a twelve-inch telescope and some complex infra-red instruments into a NASA Convair 990 jet last month and flew along a computer-determined course between Montreal and Lake Superior. At its 37,000-foot altitude, the plane was above 99.5% of the earth's atmospheric water vapor, which ordinarily confuses ground-based astronomers attempting to determine the amount of water on other planets.

By keeping a gyroscopically-controlled mirror pointed directly at Venus through a port in the plane's roof the scientists were able to deflect the planet's reflected light continuously for more than an hour into the telescope, which was mounted horizontally inside the plane. During this time, they obtained 2,000 separate patterns of Venusian light on an interferometer--a device that splits a beam of light, sends each half along a path of different length, and then rejoins them in an interference pattern of light and dark fringes. Computer analysis and averaging of these patterns by scientists at Block Associates in Cambridge, Mass., produced two of the clearest spectrograms ever obtained of Venus at high altitude. Although the spectrograms conclusively proved that there were no ice crystals in the Venusian atmosphere, they did reveal what appeared to be a significant trace of water vapor. But Kuiper and his associates were not deceived.

Desolate Planet. To cancel out the effects of any water vapor in the portion of the earth's atmosphere still above them, the airborne astronomers had also taken about 1,000 interferograms of the moon, which was close to Venus in the sky during the flight. Although the moon is known to be dry, the lunar spectrograms produced by the Block computers also showed evidence of a trace of water vapor. The vapor, the scientists knew, had been detected not on the moon but in the earth's atmosphere. Thus, by eliminating the same proportion of terrestrial vapor from the Venus spectrograms, they were able to determine the true amount of Venusian water vapor--approximately one-half of one-billionth of the Venusian atmosphere, compared with a vapor content of 1/400th of the atmosphere on earth.

The lack of water on Venus has led Kuiper to draw a desolate picture of the planet that until a few years ago was believed to be humid, fertile and capable of supporting lush extraterrestrial life. There is only a thin crust over the hot interior of Venus, he believes, accounting for the extremely high surface temperatures. The crust is probably breached in many places by volcanic vents that spew ash and carbon dioxide into the atmosphere, producing the yellowish clouds seen from earth. And there is continuous stirring of the atmosphere, Kuiper suggests, produced by surface hot spots that act like chimneys, heating the "air" above them and causing it to circulate.

"We know that the environment of Venus is very hostile by our standards," concludes Kuiper, in scientific understatement. "There is no water on the planet, and the surface temperature is close to the melting point of lead and the boiling point of sulfur. So what kind of life could you have there?"

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