A Tenth Planet?

Something new under the sun

Charles Kowal lacks the academic credentials and worldwide renown enjoyed by many of the other scientists at the California Institute of Technology. Though he is the author of some two dozen scientific papers, he has neither a Ph.D. nor a coterie of doting graduate students. What Kowal, 37, does have is a discerning eye and an insatiable appetite for scanning the sky. During the past decade, he has discovered one comet and five more that had somehow been "lost" as well as the 13th--and what may prove to be the 14th--moon of Jupiter, and 80 supernovas, or exploding stars. Last week Kowal announced an even more remarkable sighting: a small, faint object orbiting the sun between Saturn and Uranus. It could be the solar system's tenth planet.

Kowal's latest finding was based on photographs taken in mid-October through the Hale Observatories' 122-cm. (48-in.) Schmidt telescope atop California's Mount Palomar. A microscopic examination of photographic plates exposed on successive nights revealed a short, faint trail of light between the orbits of Saturn and Uranus; the object that made it appeared to be moving in relation to the stars that formed the background. Kowal promptly called Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., for help in verifying his discovery. Marsden, who serves as a clearinghouse for reports of astronomical discoveries, passed the news to Tom Gehrels of the University of Arizona. Checking plates made a week before Kowal's shots, Gehrels spotted the mysterious light trail, thus confirming the finding.

Kowal's observations indicate the object is between 160 and 640 kilometers (100 and 400 miles) in diameter--larger than most of the asteroids that orbit between Mars and Jupiter, but far tinier than the smallest of the nine planets, Mercury. It orbits the sun in the same plane as the planets and is currently about 1.5 billion miles from earth. Depending upon whether its orbital path is nearly circular or highly elliptical, the object could take anywhere from 60 to several hundred years to complete a single circuit.

Then what is "Object-Kowal," as it has been temporarily dubbed? Kowal says that his discovery "really doesn't resemble anything else we have seen," and tentatively describes the mystery object as a "miniplanet." If scientists decide that it can indeed qualify as a planet, Kowal, in keeping with astronomical tradition, will be accorded the honor of proposing its permanent name. He already has a name in mind. But for now he is keeping it secret, saying only that it is "based on traditional mythology."

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