Astronomers find four bodies beyond Neptune.

The observable edge of the solar system just got more crowded. A flurry of new findings supports the nation that the solar system's outskirts are littered with chunks of material left over from the formation of the planets.

In just one week last month, two teams of astronomers detected a total of four distant bodies that lie beyond the orbit of Neptune. One of the teams--David Jewitt of the University of Hawaii in Honolulu and Jane X. Luu of Stanford University--had previously detected the only two other bodies known to exist at these great distances (SN: 4/10/93, p.231).

Luu and Jewitt used the University of Hawaii's 2.2-meter telescope atop Mauna kea to make the first two of the new observations, scanning the same one-degree-square patch of sky in which they had made their earlier findings. The newly indentified bodies, dubbed 1993 RO and 1993 RP, appear to lie about 32 and 35 astronomical units (AU) from the sun, respectively, and form 60 [degrees] angle with Neptune's orbit. (An AU is the mean distance between the sun and Earth, about 149.6 million kilometers; Neptune now orbits the sun at about 30 AU.) The researchers reported their findings in circulars of the International Astronomical Union (IAU) late last month.

Just days after Luu and Jewitt made their discovery, another team, using the 2.5-meter Issac Newton Telescope in the Canary Islands, Spain, verified the 1993 RO sighting. In addition, these astronomers discovered two other distant objects. One of the bodies, 1993 SB, lies an estimated 33 AU from the sun, while the other, 1993 SC, appears to orbit at about 34.5 AU. Iwan P. Williams of Queen Mary and Westfield College in London, England, and Alan Fitzsimmons and Donal O'Ceallaigh of Queen's University in Belfast, Northern Ireland, also reported their Findings in an IAU circular. All four objects, which resemble asteroids, may have a diameter of about 100 kilometers.

Both teams emphasize they will need several months of observations to pin down the exact trajectories of the newly identified objects. But they suggest that the bodies may rank among the most intriguing detected in the outer solar system.

According to Jewitt, all four may belong to or have recently escaped from a primordial reservoir of comets that astronomers have theorized should exist. This ring-shaped storehouse, known as the Kuiper belt, would server to replenish the supply of short-period comets--icy remnants from the creation of the solar system, each of which visits the inner planets at least once every 200 years.

While the two bodies Luu and Jewitt found earlier seem to have circular orbits beyond Pluto, all four of the recently identified objects appear to lie closer in, just beyond Neptune's orbit. Depending on the location of the Kuiper belt, this may indicate that the two bodies beyond Pluto reside in the belt, while the other four are escapees, Jewitt suggests.

"We may have caught these bodies at the point where they're about to become Neptune crossers," he says. "Neptune will kick them in toward Uranus, and Uranus may kick them toward Saturn, and they may ultimately feed down [to the inner planets] over the next billion years."

Alternatively, notes Jewitt, the four bodies may rank as the first Trojan asteroids found near Neptune. Defined as asteroids that lead or trial a planet by about 60 [degrees], Trojans are known to exist only near Jupiter.

Based on an analysis of the past 20 million years of solar system dynamics, Matthew J. Holman and Jack Wisdom of the Massachusetts Institute of Technology reported in the May ASTRONOMICAL JOURNAL that Saturn, Uranus, and Neptune could each have a stable family of Trojans. A more extensive analysis by the researchers also indicates that Kuiper belt residents could "leak" more easily into the inner solar system than previously thought.