Spaceman's Rat-a-Taf-Tat

When the first human rides into space and reaches 80 miles up, he will hear alarming sounds: the sharp pings of cosmic dust particles hitting the skin of his capsule. Harvard Astronomer Professor Fred L. Whipple last week told an Air Force space conference at San Antonio that the earth is surrounded by a shallow but unexpectedly dense cloud of dust that can be detected only by the noise that it makes when it hits space vehicles equipped with listening devices.

The particles, said Whipple. are extremely small, averaging 300 billion to the ounce. They are thickest 80 miles up. Farther out in space the dust cloud thins quickly; it almost disappears at the distance of a few earth diameters (8,000 miles).

Whipple thinks that the earth's dust layer is the remains of comets, which bring fragile blobs of material from the outer fringes of the solar system. He suspects that when these cosmic puffballs pass through the Van Allen radiation belts that girdle the earth, they collect strong electric charges that make them pop. breaking them into microscopic dust particles that stay near the earth, perhaps following orbits like near-in satellites.

Most of the particles, says Whipple, are probably too small to be dangerous, but they make a loud rat-a-tat-tat sound. To the space traveler, the chief harm that they can do is psychological. So Whipple suggests that the nerves of spacemen be shielded from this hazard by surrounding their capsule by a thin metal shell that wi!! intercept the speeding dust particles but will not transmit to the capsule the unnerving sounds that they make.

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