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The Farthest Encounter
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15328 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
8 / 1989 |
3,915 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. |
It is a terrible place. Blue-tinged clouds of choking methane swirl in an icy atmosphere 10,000 miles deep. The light, even at cloudtop level, is weak and cold; the Sun is only a pinpoint in the starry sky. Somewhere in the vicinity of that pinpoint is Earth, invisible to the naked eye, as are all the rocky worlds in our planetary neighborhood: Mercury, Venus, and Mars. This is a world only slightly more attractive than the bitterly cold, empty abyss of outer space itself. Here we finally come to the end of a mighty procession of giant planets. Here we reach the last outpost of the Solar System, currently the remotest domain of the Sun's kingdom. The huge, striated orb that slowly parades through this distant arena carries a name from a civilization that never knew of its existence. This is Neptune.
For two years, Neptune has, unknowingly, been on a rendezvous path with a strange visitor. Early this August, a small, old-looking contrivance, launched a decade earlier from a tiny inner planet, will dart to within 3,000 miles of the blue-green behemoth's churning atmosphere. For a few hours, it will swing by the planet, furiously taking pictures and making measurements. Passing southward, it will refocus its cameras and instruments on Triton, the larger of Neptune's two known moons. And shortly thereafter, it will be gone. The first-ever encounter, a dozen years in the making, of a man-made object with this last planetary giant will be over in less than a dozen hours.
The Grand Tour
Although the launch of Sputnik I in 1957 galvanized the world, three decades later most people hardly notice when yet another satellite is thrust into space. The Earth is presently ringed by thousands of satellites used for communication, mapping, weather monitoring, and defense. But only a few launches have attempted to send spacecraft farther than this encircling swarm. And only four have ever headed for the outer Solar System, the dark and distant compass of the five farthest planets: Jupiter, Saturn, Uranus, Neptune, and Pluto.
While Jupiter and Saturn are easily seen with the naked eye and were well known to the ancients, Uranus, Neptune, and Pluto were discovered only by the aid of the telescope during the last two centuries. Pluto is certainly the "oddball" among the outer planets. Not only is it small (approximately 1,400 miles across), but its orbit is both very elliptical and tilted with respect to those of the other planets. At the moment, this peculiar orbit has placed Pluto even closer to the Sun than Neptune, which
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