Somewhere, Tonight, a World Is Ending

July 13, 1994|By GWYNNE DYER

LONDON — If there is life deep within the atmosphere of Jupiter (it would need a different biochemistry than ours, but it is possible), then it is in bad trouble.

Beginning Saturday, Jupiter will suffer the equivalent of a major nuclear war every eight hours or so for six Earth days. By the end of the bombardment, things could have changed there as much as they did 65 million years ago on Earth, when a giant meteorite crashed into the Gulf of Mexico and ended the age of the dinosaurs.

Comet Shoemaker-Levy 9 was probably about the size of the doomsday rock that got the dinosaurs when it passed Jupiter in July 1992, but the gravity of the largest planet in the solar system tore the comet into 21 fragments. Two years later, those fragments, each up to a mile in diameter or even more, are heading straight for the Jovian atmosphere.

Observers on Earth will not see the first fragments strike, since they will hit the side of Jupiter that is turned away from us -- but we may actually see the flash of their detonation reflected back to us from the Jovian moons. And what happens to anything living in Jupiter's extremely dense atmosphere? That depends.

Partly, it depends on what the comet was made of. If it was mostly ice and other low-density, easily fragmented materials, then each huge chunk may break up in the first second after hitting atmosphere, and produce nothing more than a few hundred high-altitude explosions of low-kiloton range, the equivalent of Hiroshima bombs.

That is the minimum hypothesis. Even our own small planet endures at least a dozen or so blasts of that scale each year, but the meteorites explode so high in the atmosphere that only satellites detect them. Giant Jupiter, with an atmosphere a hundred times as deep and a thousand times as dense, would absorb that sort of assault without a tremble.

But if the Shoemaker-Levy comet contained large amounts of hard rock or metal, it will be a quite different story. Then we're talking about chunks of rock the size of Mount Fuji falling out of the sky at 140,000 miles an hour.

No time for bits to break away, no time for friction to slow the mountain down. Within five seconds it is 200 miles deep in the atmosphere, pushing a shock wave as dense as steel ahead of it. Then it explodes, vaporizes -- and releases 20 million megatons of energy. Forget about nuclear war: All the

nuclear weapons on Earth pack less than 2 per cent of that energy.

Imagine a blast of hard radiation that can sterilize any life within hundreds of miles, a plume of superheated gas shooting 2,000 miles above the atmosphere like the fountain of water above a depth charge -- and a shock wave, magnified by the dense atmosphere, that travels right around the planet and is strong enough to rupture living organisms. Now imagine this happening not once, but a dozen times or more over six days, in strikes distributed randomly around the planet. Jupiter is very big, but that could be enough to do the job. All the complex, multi-cellular life forms on Jupiter may be facing extinction this month -- if they happen to exist.

We have no evidence that they do, of course. We just know that the organic compounds that are the chemical building blocks of life abound in outer space, and may well provide the ''seed'' from which life on planetary surfaces grows.

We know that the middle level of the Jovian atmosphere, like the land and seas of Earth, is a potentially hospitable home for life (though life of a radically different chemical structure from our own).

And we know that here on Earth, at least, life flourishes in any nook or cranny, however inhospitable, where it can get a toehold. So there may not be life on Jupiter, and there almost certainly is nothing that we would call intelligent life -- but there could be. If there is, and you happen to be of a religious disposition, now would be a good time to say a prayer for it.

Say the prayer anyway, because some planet, somewhere, is almost certainly facing a mass extinction.

Just in the past two or three years, a rapidly growing heap of evidence has finally begun to confirm the hypothesis that life is commonplace in the universe. So commonplace that calamities like the one that hit this planet 65 million years ago, and the one that may be nearing Jupiter now, are a daily or weekly event even within our local group of galaxies.

Planets, it turns out, probably accompany almost all stars for at least part of their lives.

In June the Hubble Space Telescope, surveying a group of young stars in Orion, found that at least half of them were surrounded by the telltale flattened disks of dust that indicate planets are forming around them, though they are on average only 300,000 years old.

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