Comet find: five easy pieces.

Some planetary scientists consider comets to be fragile objects, breaking apart easily as soon as their crusty surface is broken (SN: 5/7/94, p.298). A case in point: the cosmic traveler found by amateur astronomer Donald E. Machholz on Aug. 13.

Two weeks later, another astronomer found an icy fragment belonging to the comet. Then two additional astronomers independently discovered a third chunk on Sept. 2 and 3. Several researchers identified yet two more pieces on Sept. 4 and 5. The verdict: The comet, dubbed Machholz 2, consists of a bright parent body plus at least four additional fragments.

The most recent example of a fragmented comet, Shoemaker-Levy 9, broke into some 21 pieces near Jupiter 2 years ago and then plowed into the planet last July. In contrast, Machholz 2 hasn't ventured near a planet in the last 100 years or so and isn't likely to in the next 100 years, says Donald K. Yeomans of NASA's Jet Propulsion Laboratory in Pasadena, Calif. His analysis disputes media accounts that the comet may soon be heading toward Earth.

Yeomans proposes that Machholz 2 broke apart because of internal activity, perhaps a structural change in some of the comet's supply of frozen water.

Brian G. Marsden of the Smithsonian Astrophysical Observatory in Cambridge, Mass., notes that although the fragments line up over a distance of some 1 million kilometers, the relative separation of the five pieces indicates that they clump as one group of two and another group of three. He suggests that the two groups of fragments were created during the comet's last two closest approaches to the sun. Machholz 2 passes near the sun once every 5.2 years.

That would mean that some of the pieces have survived for more than a decade, an intriguing finding since astronomers generally believe that after a few weeks, most fragments crumble into pieces too small for a telescope to detect.