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Nature of comets reconsidered
Southwest Research Institute
August 8, 2003
"It also now seems inevitable that most comets from the Kuiper Belt, though constructed of ancient material, cannot themselves be ancient -- instead they must be 'recently' created chips off larger Kuiper Belt Objects, formed as a result of violent impacts," says Stern. "This is truly a paradigm shift. Many of the short-period comets we see aren't even ancient!"

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some oldies:

Comet Cloud May Be Quite Thin
by Vanessa Thomas
In 1950, Dutch astronomer Jan Oort noticed these comets come from every direction and have orbits that reach about 50,000 astronomical units (AU) away from the sun. Paul Weissman of the Jet Propulsion Laboratory and Alan Stern of the Southwest Research Institute believe that many of the planetesimals that planetary scientists thought were ejected into the Oort Cloud actually were pulverized while still among the giant planets. Computer models by Stern and Weissman show that most of the large chunks and other debris were destroyed in collisions amongst themselves before the giant planets had a chance to use their gravitational influence to whip survivors out toward the solar system's edge.
Jupiter's Composition Throws Planet-formation Theories into Disarray
by Robert Roy Britt
Examining four-year-old data, researchers have found significantly elevated levels of argon, krypton and xenon in Jupiter's atmosphere that may force a rethinking of theories about how the planet, and possibly the entire solar system, formed. While lead researcher Tobias Owen does not put much stock in the idea that Jupiter might have migrated inward to its present position, other scientists on the team say the idea merits consideration. Owen expects the probes will find similarly high levels of noble gases in Saturn, Uranus and Neptune. Hints of these gases have even been found in the thick atmosphere of Venus, another planet now begging more study.