SCIENCE / ASTRONOMY : 2 Discoveries May Point to Comet Origins

Astronomers in Hawaii and California, in separate discoveries, said Monday that they have found a collection of fuzzy interplanetary ice balls in the outer reaches of the solar system that should shed new light on where comets are born and, perhaps, how they die.

In the first discovery, U.S. Geological Survey astronomers at the Palomar Observatory in San Diego County observed bright “pearls on a string” near Jupiter. The objects--at least 17 of them--are believed to be remnants of a comet that was either crushed by the giant planet’s gravity or was swept close enough to the sun to partially melt and fall apart.

The second finding, by two astronomers from the University of California and University of Hawaii, was of a 155-mile-wide ball of ice and rock at or beyond the orbit of Pluto. It is the second such object found by the astronomers in a year and adds weight to the theory of the Kuiper Belt, a postulated “comet nursery” at the outer edge of the solar system.

Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., estimated that this new object is between 3.5 billion and 5.2 billion miles from the sun. Pluto, the most distant planet in the solar system, has an elliptical orbit about 3.6 billion miles from the sun.

The Kuiper Belt of comets is named for Gerard P. Kuiper, the Dutch-born American astronomer who proposed that planets condensed out of a turbulent cloud of gas and dust around the sun soon after it was born.

“Comets formed in the earliest days of the solar system but were never gobbled up into a planet,” said David C. Jewitt of the University of Hawaii, who discovered the distant object with Jane X. Luu of UC Berkeley. “They are the leftover space debris of the building of the solar system.”

As such, he said, they can help scientists better understand the processes that shaped the solar system then and may still influence it today. Comets also could help astronomers to see how planets may form around other stars.

The fractured comet was discovered near gaseous Jupiter last Wednesday through a terrestrial sky clouded with rain and fog. The cluster of fragments has been named Comet Shoemaker-Levy in honor of the astronomers--Carolyn S. Shoemaker, her husband Eugene M. Shoemaker, and David H. Levy--who first recorded the objects last week on some damaged film they had scrounged to save money.

Although 25 comets were known to have fractured in the past, the breakup of this ball of dirty ice has caused a mild sensation among astronomers because it has cleaved into so many pieces--17 counted so far--and the pieces are all large enough to be relatively bright and easily seen from Earth.

“My jaw dropped open when I saw it go by on the screen,” Jim Scotti of the University of Arizona told the Washington Post. Scotti, at the Kitt Peak Observatory near Tucson, was one of several astronomers to have confirmed the sighting in observations from Massachusetts to Hawaii. He counted 11 fragments, compared to the five pieces originally reported by the USGS astronomers.

On Monday, Luu and Jewitt reported that they could count 17 distinct pieces using the University of Hawaii Institute for Astronomy’s 88-inch telescope atop Mauna Kea.

Jewitt said the comet fragments appeared to be all in a row, “strung out like pearls on a string.”