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Caltech astronomer Maciej Konacki, for example, has found the first planet in a triple-star system. Konacki dubbed his find the "Tattooine planet," after a planet with two suns in its sky in the Star Wars movies. The planet orbits the main star of the system HD 188753. The three stars are as close to each other as Saturn is to the Sun. "How that planet formed in such a complicated setting is very puzzling," Konacki said. "I believe there is yet much to be learned about how giant planets are formed."

At the smaller end of the planet spectrum, a team led by Geoffrey Marcy of The University of California, Berkeley, has found the latest "smallest-known planet." Because it is only 7.5 times as massive as Earth, team member Paul Butler called it "EarthÕs bigger cousin." The planet takes two days to orbit the red dwarf star Gliese 876, 15 light-years from the Sun and already known to harbor two giant planets. The "new" planet is too hot to have life as we know it, the astronomers say, because it orbits only two million miles from its star.

Another team of astronomers has discovered a planet with a solid core that is 70 times as massive as Earth, the largest core yet found. The team says it confirms the "core-accretion" theory of planet formation, which states that planets grow a core first, then acquire gas through gravity. Because the planet passes directly in front of its star, HD 149026, on each orbit, the team was able to calculate "its physical size, whether it has a solid core, and even what its atmosphere is like," said team leader Debra Fischer of San Francisco State University.

Last, Paul Kalas of UC-Berkeley used Hubble Space Telescope to bolster longstanding evidence that a planet orbits Fomalhaut, a nearby star that is prominent in EarthÕs night sky. For two decades, astronomers have known that a dusty belt of material, much like the SunÕs Kuiper Belt, surrounds Fomalhaut. Now HubbleÕs sharp vision shows that the belt has a sharp edge, indicating a zone swept clear by the gravity of an orbiting planet. Rebecca Johnson