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The Search for Other Worlds
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14176 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
1 / 1988 |
3,321 Words |
| Author
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Seth Shostak
Seth Shostak, who currently resides in Mountain View,
California, has spent most of his career as a research radio
astronomer. |
Last summer, at a joint meeting of the Canadian and American Astronomical Societies held in Vancouver, British Columbia, astronomers described new observations that suggest that planets may be a dime a dozen. This result, the product of six years of careful work by three Canadian researchers, caught the fancy of both scientist and laymen. For it is a fact that we still do not know for certain if there are any planets in the Universe other than the nine that circle our own Sun.
The existence of extrasolar planetary systems (that is, planets orbiting other stars) would be an exciting discovery from several points of view. To begin with, it would be an important datum in understanding how stars are born. But beyond the basic astronomical interest, the presence of other planets is a critical factor in the argument for extraterrestrial life. For anyone wishing to believe that there is life on other worlds, it would strengthen the case to first establish that there are other worlds.
How to Find a Planet
The technique for finding planets has always been the same: Search the skies for objects that move relative to the general field of stars.
The astronomers of classical times knew of the five naked-eye planets: Mercury, Venus, Mars, Jupiter, and Saturn. Several of these objects are quite bright (Venus can even throw a noticeable shadow), but that's not entirely the point. All five objects move relative to the sky's stellar backdrop. The planets slowly (and in the case of Mercury, not so slowly) shift their location from one constellation to another. No wonder, therefore, that the Greeks applied the word planet, meaning "wanderer," to such objects.
The planets wander, of course, because they are relatively nearby and are continuously circling the Sun. After Isaac Newton put the motion of the planets on a sound theoretical footing with his gravitational theory, astronomers had a precision tool for predicting the position of the planets. "Wandering" gave way to "orbiting."
Newton's theories were so successful in describing planetary motions that even small deviations from predicted orbits were carefully noted. Uranus, the first planet to be discovered in modern times, was located with a small telescope by the English astronomer John Herschel in 1781. But small eccentricities were soon perceived in Uranus' orbit. By the beginning of the
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