Astrophysics: Venus Revealed

Out of the raw data transmitted back to earth from Russia’s Venus 4 and the U.S.’s Mariner 5 spacecraft, scientists last week pieced together a picture of Venus as a place of unbearable heat, a dense and noxious atmosphere, and nightmarish optical effects.

If a visitor to Venus were insulated and refrigerated against the 536° F. surface temperature, he might survive long enough to see both a sunset and a sunrise, which occur 59 earth days apart. When it was high in the sky, the sun would appear as a familiar disk—if it could be seen through the murky Venusian clouds. But as it set, according to Stanford University Engineer and Physicist Von R. Eshleman, the disk would gradually diffuse itself around the entire horizon as a glowing band for the remainder of the night; sunlight is so bent, or refracted, by the dense atmosphere that it circles around to the dark side of the planet. At dawn, nearly two earth months later, the band would reassemble into a disk that would then slowly rise.

View from a Bowl. The high refractivity of the Venusian atmosphere could have other bizarre effects. Looking toward the horizon with a powerful enough telescope, the visitor might be able to see the back of his own head. And wherever he was, he would appear to be standing in the center of a depression, or bowl, looking up toward the horizon. Concluded Eshleman: “We can now say that Venus is not only hell, but a hellhole.”

Mariner 5’s findings, released last week, agree generally with data sent back by Russia’s Venus 4 and its landing capsule. Neither spacecraft found evidence of Van Allen-like radiation belts around Venus, both reported hydrogen coronas and found that carbon dioxide was the principal constituent of the Venusian atmosphere. Mariner’s finding that the atmosphere was “at least” 7 to 8 times as dense as the earth’s does not contradict more precise Russian data showing densities 15 to 22 times as great.

But there were differences in results. Although the Russians did not detect a Venusian magnetic field, Mariner discovered slight magnetic activity that could have come either from a field less than 1/300th the strength of earth’s or simply from the interaction between the solar wind and the Venusian ionosphere. The Russians at first reported that carbon dioxide comprised 98% of the Venusian atmosphere, but later revised the figure down to between 90% and 95%, closer to Mariner’s reported 72% to 87%. And while Mariner could find no evidence of oxygen in the atmosphere, the Venus 4 capsule reported a trace (.4 of 1%) of oxygen and some water vapor (1.6%).

High Threshold. The Russians also came to the rescue of U.S. scientists, who had been at a loss to explain preliminary Venus 4 reports that there was no nitrogen in the Venusian atmosphere (nitrogen accounts for 78% of terrestrial air). Backing off slightly, the Soviet scientists explained that the nitrogen-gas analyzer aboard the capsule had a “signal-detection threshold” of 7%; thus it would have been unable to detect smaller percentages of the gas.

Although Mariner came no closer than 2,480 miles from Venus, it made some observations unreported by Venus 4. The night sky of Venus, Mariner found, emits a faint ultraviolet glow that scientists believe could be caused by chemical reactions in the atmosphere, lightning or bombardment by solar radiation. And at the time of flyby, Mariner’s signals revealed, the precise distance between Venus and the earth was 49,563,222 miles.