Big Burn

Astronomers take the atomic bomb in stride. They know there are more terrible ways in which this planet might be destroyed. Last week Astronomer Robert Coles of the Hayden Planetarium summed up, in Sky and Telescope the latest "astronomical facts concerning the end of the world": About a ton of pulverized meteorites fall on the earth's surface each day, do no damage. But, points out Coles, the famed 1908 meteorite that fell in northern Siberia showed what a meteor could do. It knocked forests flat for 30 miles, blew a man off his doorstep 50 miles away. Its roar was heard more than 400 miles.

Astronomers believe that meteors are the debris of broken comets, and they shudder to think what would happen if a comet head itself, approaching at some 45 miles per second, were to crash into the earth. Astronomers' guesstimate of the chances: once in 100 million years (age of the earth: two billion years).

But a comet collision would be a cream-puff blow compared with an encounter between the earth and an asteroid. These small bodies, believed to be pieces of a planet once located between Mars and Jupiter, have highly eccentric orbits and often shoot close to the earth. In 1937 a small asteroid, Hermes, missed the earth by only 500,000 miles -- a bare stone's throw as interplanetary space is reckoned.

At the great speed of planetary flight (the earth's is 18 m.p.s.), a collision between the earth and a moderate-sized asteroid (diameter: 100 miles) might well smash a continent.

Such explosions, Coles says, would not necessarily mean the end of the world. Astronomers are betting on the sun to do that job. They have been made more & more uneasy by the number of novae in the universe -- stars which, for some unknown reason, suddenly flare up to thousands of times their normal brilliance.

Says Coles: "Since no one knows why certain stars behave in this violent fashion, we cannot be sure that such a catastrophe will not some day befall our sun.

A nova-like flare-up of the sun might happen tomorrow." If it did, the sunny side of the earth would be burned to a crisp in half an hour, the oceans would boil away in live steam. Within a few days the world would be vapor.

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