Shocks from the Sun

Early last week the bright face of the sun showed even brighter spots, each of them a gigantic explosion tossing gas and magnetism deep into space. Blasts of charged particles crossed millions of miles of space and smashed into the earth's magnetic field. In each case there was no warning of the approaching storm; it hit the earth with a sharp initial pulse, lasting about a minute and followed by violent fluctuations.

The sharp first pulse has long been a puzzle. But last week Dr. Arthur Kantrowitz of the Avco Research Laboratory at Everett, Mass, reported that he and his scientists had successfully simulated this solar phenomenon in the laboratory, and offered an explanation for it.

The theory that led to the experiment goes back to 1953, when British Cosmologist Thomas Gold suggested that the initial pulse from the sun might be a shock wave analogous to the shock wave produced in air by a plane breaking through the sound barrier. Professor Gold knew that gas in interplanetary space is too thin to carry ordinary shock waves, which propagate by gas molecules bumping against each other. But solar shock waves, he argued, are different. They are caused by solar magnetic fields expanding suddenly into space and pushing ionized gas ahead of them. "It is a bit like a weather front," he explains. "Before, you are living in a very quiet zone. Suddenly a front sweeps over, and behind this front is a region of great disturbance and turbulence."

In 1957, when Gold came to Cambridge, Mass, to teach at Harvard, he found that Dr. Kantrowitz and a team of Avco scientists were attempting to prove in the laboratory that his waves can really exist. Their plan was to build a laboratory-scale model of a solar eruption.

As described by Dr. Kantrowitz last week, Avco's miniature sun is a tube 30 inches long filled with very low-pressure gas. When a 4 billion-watt electrical spark from a bank of condensers is discharged across the end of the tube, the magnetic field that surrounds it should expand--so said Gold's theory--into the tube, pushing the gas ahead of it in a small, tame version of a solar shock wave.

This is just what happened. Photocells along the tube reported that a thin, luminous wave raced along it at 45-50 cm. per microsecond (about 1,000,000 m.p.h.).

Dr. Kantrowitz' indoor waves are only about half as fast as the waves that Professor Gold theorized as coming from the sun. But the difference in speed is easily accounted for by the fact that the gas in the tube is not nearly so thin as interplanetary gas. Such waves may be among the disturbances that instruments in the moon-probe rocket Pioneer IV detected deep in space, 10,000 miles beyond the outermost limit of the Van Allen radiation. Dr. Kantrowitz suspects that his newly discovered waves may prove a serious threat to interplanetary travelers of the future.

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