3D Vision: Meteors

Date: 11/14/98

Publication: The Nation

Wish upon some shooting stars

3D Vision by James Fahn

The Leonid meteor shower will provide a good opportunity to think about where we came from, and where our planet is going. By James Fahn

Even in these troubled times, that's a lot of wishes to make.

In fact, even if your life is already fine and dandy, consider sacrificing some sleep to catch the celestial fireworks show. Although the Leonids recur every 33 years, some astronomers think this shower will be particularly spectacular, maybe even a once-in-a-lifetime event.

The Leonids are named after the constellation Leo which will appear in the eastern portion of the sky on the night in question -- because that is where the shooting stars will seem to be shooting from. But their fiery trails could extend across much of the heavens.

Of course, the real source of the meteors is not the constellation itself but rather a comet named 55P/Tempel Tuttle, which makes its pass around the sun about three times every century, leaving a trail of debris behind in its wake. On Nov 17-18, the Earth will only pass through an edge of this cometary cloud -- the closest we'll get to its centre is about 1.3 million kilometres, a distance three times greater than the distance to the moon -- but that still should be enough to catch our attention.

The meteors themselves are mostly tiny pieces of dust which burn up high in the atmosphere. But larger objects can sometimes can leave luminous trails that last for minutes, or go out with a fiery explosion, and the largest of meteors can survive to crash onto the Earth's surface, thus achieving the label 'meteorite'.

Nowadays, though, a meteor shower can do quite a bit of damage even before it hits the atmosphere, for a lot has changed since the last time the Leonids came around back in 1966. There are now around 600 active satellites up in orbit which can expect to receive at the very least a ''sandblasting'' from the microscopic particles travelling at speeds upwards of 260,000 kilometres per hour. Wherever possible, these spacecraft will be maneuvered out of harm's way, but there is a chance that some could be significantly damaged.

That said, satellites are always in danger of being hit by debris of a more prosaic origin: the growing volume of ''space litter'' which has been carelessly left behind in orbit by humans. The problem is growing exponentially worse as more objects collide with each other, creating yet more space junk, so that now even the authorities are beginning to acknowledge that one day there could be a man-made environmental crisis in orbit.

Mankind has been changing other things, too, most notably our own atmosphere. British scientists recently announced that the it has in fact been shrinking, probably as a result of the greenhouse gases we have been emitting.

Radar measurements taken by the British Antarctic Survey over the last 38 years show that the average height of the atmosphere has fallen by about eight kilometres, which isn't very good news. So if you are planning on making lots of wishes next week, you just might want to spare a few for the layer of air which lets us live.

Actually, the height of the entire atmosphere varies from around 300 kilometres on the nocturnal side of the planet to 350 kilometres in daylight, as the heat of the sun causes gases in the top layer to expand. But whereas in the lower atmosphere greenhouse gases such as carbon dioxide and methane help to trap heat and prevent it from escaping into space -- thus leading to global warming -- in the upper atmosphere they repel the sun's heat and have a cooling effect, thus causing the atmosphere to shrink. That's the theory put forth by the British, at any rate.

It's not clear whether this shrinking would actually give meteors a greater chance of making it through the atmosphere to hit the Earth. But if you do come across a meteorite, you might want to take good care of it. At the going market rates, they are worth thousands of baht per kilogram.

And with good reason. Meteorites can tell us a lot about the solar system, and maybe even something about where we came from. It was only a couple of years ago that NASA scientists discovered what appears to be the fossilised remains of bacteria in a meteorite that originally came from Mars.

There is an even more interesting theory, known as ''panspermia'', which holds that life on Earth actually originated from space-borne bacterial spores that arrived here on meteors. No, this is not something dreamed up by the creators of The X-Files, but rather a scientifically testable, if still controversial, hypothesis expounded by a couple of well-respected British astronomers, Fred Hoyle and Chandra Wickramasinghe.

Through their spectroscopic studies of space and the light from distant stars, they claim to have found evidence that bacterial life does indeed exist floating between the stars, and there seems to be a growing scientific consensus that at the very least space contains the ''ingredients'' for life.

What's more, Hoyle and Wickramasinghe have proposed that comets, which are mostly made up of water-ice, serve as a kind of delivery system, carrying these bacterial spores across galaxies and protecting them from radiation damage. (A good explanation of this theory, and a broader Theory of Cosmic Ancestry which extends the concept of Gaia to include the entire universe, can be found on the Internet at www.panspermia.com.)

Perhaps you find it hard to believe that our origins may have actually come from outer space, but it's a theory that dovetails nicely with the tradition of making a wish when you see a shooting star. After all, it may have been a similar shower of ''cosmic rain'' which first brought life to our planet billions of years ago.

So by making a wish upon a shooting star, we may actually be sending a kind of prayer to our ancestors, and that's something many of us already do every day.