Lifting Venus' Veil

While the U.S. space program has concentrated on the exploration of the moon and Mars, Soviet scientists have trained their sights on cloud-enshrouded Venus. Since 1961, Russia has launched at least ten missions to Venus, most of them intended to land instrumented packages on the surface of the planet; by comparison, the U.S. has undertaken only two less ambitious flyby probes. The persistent Soviet effort has paid off. After careful analysis of data from Venera 8, which transmitted signals for 50 minutes after making a landing in July, Russian scientists have lifted still more of the veil from the earth's closest planetary neighbor.

The most significant of Venera's revelations is that the chemical composition of at least part of the surface is similar to the earth's. Venera's gamma-ray spectrometer determined that the landing area contained radioactive potassium, uranium and thorium in approximately the same ratio in which they appear in many volcanic rocks on earth. This, in turn, indicates that Venus, like the earth, Mars and the moon, is "differentiated"; that is, the planet was once hot enough for its material to soften and flow. During this period, the heavier elements settled toward the core while the lighter ones, taking radioactive elements with them, rose to the surface to form a crust.

Venera confirmed readings by earlier Soviet and U.S. missions indicating that the temperature on the surface of Venus is about 880DEG F--hot enough to melt lead. The spacecraft also revealed that Venusian surface material is only about half the density of soil on earth.

Most of the Venusian hemisphere facing the earth was in darkness when Venera 8 arrived, but the Russians managed to land their spacecraft in the narrow crescent that was illuminated by the sun. With the aid of Venera's photometer, Soviet scientists could determine that about two-thirds of the solar radiation striking Venus penetrates the thick cloud cover and reaches the surface. Thus there is a long (about 116 earth days) period of daylight as well as a lengthy nighttime on the surface of Venus, which revolves on its axis only once every 243 earth days. Surprisingly, the surface does not cool during the long period of darkness; the "greenhouse effect" of the planet's atmosphere (consisting largely of carbon dioxide) keeps heat from radiating away at night.

Passing through that atmosphere on the way to its landing, Venera detected traces of ammonia, confirming earlier observations made by earth-based telescopes. By tracking Venera's descent, the Russians also measured Venusian winds of 110 m.p.h. at an altitude of 30 miles, comparable to the speed of the earth's jet streams. Near the surface, however, they clocked winds of only about four m.p.h. Some scientists believe that the winds are stirred up by Venus' rotation, since they seem to blow only in the direction of the planet's spin.

Venera's highly productive mission (it broadcast from the surface for 27 minutes longer than Venera 7) is attributed by Soviet scientists largely to better insulation and a redesigned cooling system that prechilled the spacecraft in cold interplanetary space just before its rendezvous with Venus, allowing it to survive longer in the searing heat. Whatever the reason for success, Venera's mission may cause some changes in U.S. space plans. NASA scientists had proposed a 1980 Venus mission equipped with devices to learn if the planet was indeed differentiated. Now that Venera has apparently answered that question, U.S. scientists will press for equipping the flights with some kind of imaging system--perhaps a radar altimeter or a side-viewing radar--that will enable man for the first time to "see" beneath the murky veil of Venus.

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