News from Venus

Across 36 million miles of space, the incredibly intricate instruments of Mariner II flashed their coded reports. But what had the spacecraft seen and recorded in its triumphant dash past Venus (TIME, Dec. 21)? Though the answers will be as many and varied as Mariner's many experimental observations, the first data deciphered by scientists seemed disappointingly empty: as far as Mariner's magnetometer could tell, Venus has no magnetic field. But even this negative finding has fascinating implications. It hints that Venus may be a more attractive hunk of space real estate than scientists have supposed.

Unlikely Field. At last week's Philadelphia meeting of the American Association for the Advancement of Science, Physicist Paul J. Coleman of the University of California said that the spacecraft's magnetometer worked perfectly during the flyby, but it reported no increase of magnetism. Coleman reminded his colleagues that Venus may have spots of strong local magnetism that do not make themselves felt far from the surface. But this is unlikely, and if Venus has a single magnetic field similar to the earth's, it must be less than 5-10% as strong.

Spoilsport radio astronomers on earth have been measuring radio waves from Venus and drawing the conclusion that the planet's surface temperature must be at least 600 DEGF., which is about as hot as molten lead and much too hot for earth-type life. But they may have been fooling themselves. The earth's strong magnetic field acts as a buffer that deflects most cosmic rays. If Venus has little or no magnetism, the rays must hit the top of its atmosphere, perhaps creating an ionized layer that looks hot when examined by earth's radio telescopes. Under this layer (if it exists) and under the Venusian clouds, the planet's surface may be cool enough to support some kind of life.

Uncomfortable Winds. Coleman pointed out that the earth, which has a strong magnetic field, rotates once in 24 hours, and many scientists believe that its magnetism is caused by some dynamo effect connected with the rotation. Jupiter, which rotates once in about twelve hours, has a field much stronger than the earth's, while the moon, which rotates once in 27 days, has apparently no field at all. So the fact that Venus has little or no magnetic field may mean that it rotates slowly. It may keep the same face toward the sun during its 225-day orbit, as some astronomers believe.

What effect would this slow rotation have on Venus' value as a potential spot for space colonization? The answer is not certain, but it is not promising. The dark side of Venus does not seem to be much cooler than the sunlit side; if Venus does not rotate with respect to the sun, something must carry heat from one side to the other. That something may be fierce winds that circulate through the Venusian atmosphere, perhaps making the surface an uncomfortable place to live.

Scientists may soon feel more certain of their new theories. Coleman reported that Mariner II's instruments, designed to measure heat and microwaves, also seemed to work perfectly during the flyby. Their findings will be reported next month.

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