Over the past decade, planetary astronomers have begun to seriously explore the Edgeworth-Kuiper Belt of comets and "ice dwarf" worlds near the edge of the solar system. During an invited lecture at the International Astronomical Union (IAU) General Assembly today, Dr. Alan Stern of Southwest Research Institute (SwRI) will describe new theories about the early solar system made possible only by extensive studies of the Edgeworth-Kuiper Belt.

"This region is planetary science's equivalent of an archeological dig into the history of the ancient outer solar system," he reports. Stern, a planetary astronomer, is director of the SwRI Space Studies Department in Boulder.

Illustration of Kupier Belt. Photo: NASA/STSci

The Edgeworth-Kuiper Belt, first discussed in the 1940s and early 1950s by British astronomer Kenneth Edgeworth and Dutch-American astronomer Gerard Kuiper, was discovered by telescope in 1992. Since then, more than 300 objects have been detected in this disk-like ensemble of comets and larger objects beginning just beyond the orbit of Neptune. Current estimates, based on the number of objects discovered to date and the fraction of sky surveyed in those searches, indicate that at least 100,000 miniature icy worlds and more than one billion icy comets dot this region.

Because of the Edgeworth-Kuiper Belt's isolation and its distance from the warmth of the sun, which can drive chemical reactions, it serves as a kind of "time capsule," teaching astronomers about the early solar system. "As we probe the Edgeworth-Kuiper Belt more deeply, we are seeing an increasing number of clues to the solar system's ancient past, 4 to 5 billion years ago," says Dr. Dan Durda, another SwRI planetary astronomer.

Stern will describe the lessons gleaned from Edgeworth-Kuiper Belt studies, performed at SwRI and elsewhere, during this session. Among those topics addressed will be:

• The discovery that the solar system, like many now seen around other stars, is surrounded by a belt or disk of debris and small planets.
• The discovery that Pluto is not an oddity beyond the planets, but is instead a miniature planet itself, and is the "king of the Kuiper Belt."
• The discovery that most short-period comets - those comets with orbits of less than 200 years and which are known to originate in the Edgworth-Kuiper Belt - are recently created fragments from collisions between the larger icy objects in this region, not ancient relics as previously thought.
• The discovery that early in the solar system's history, the Edgeworth-Kuiper Belt was apparently 100 or more times more massive and populous than it is today.

"These discoveries are something we could barely have guessed at just a decade ago, and they are so fundamental that basic texts in astronomy will require revision," says Stern.

Beyond the facts already uncovered by Edgeworth-Kuiper Belt studies lie new questions about this region that may reveal equally exciting findings about the history and architecture of Earth's solar system. Does the Edgeworth-Kuiper Belt extend far beyond the distance at which new objects are presently being discovered? Are some Edgeworth-Kuiper Belt objects in orbits similar to Pluto's; that is, are they fragments of the titanic collision believed to have created the Pluto-Charon binary planet system? Are there bodies the size of Pluto (>2,000 kilometers in diameter) or even larger waiting to be discovered beyond the Edgeworth-Kuiper Belt?

"Answers to these and other questions, as well as discoveries we cannot predict surely await us," says Stern. "Some of these results will come from the increasingly capable array of ground-based astronomical instruments. Most exciting, however, will be NASA's planned Pluto-Kuiper Express mission, set to launch in 2004. Pluto-Kuiper Express will fly by Pluto-Charon, making detailed maps and compositional measurements, and then continue its reconnaissance into the Edgeworth-Kuiper Belt to make one or more close flybys of worlds lying even farther away."

SwRI is an independent, nonprofit, applied research and development organization based in San Antonio, Texas, with more than 2,700 employees and an annual research volume of more than $300 million.