First they were novelties; now they are enigmas. A bumper crop of newfound planets contains some of the oddest worlds known, mixed with hints that there may be other solar systems that resemble our own lurking among the legions of cosmic weirdos.
PLANETS WITHOUT SUNS. Maria Rosa Zapatero Osorio of the California Institute of Technology and her colleagues just spotted 18 solitary planets, inexplicably not circling any stars, in a young stellar cluster in Orion. These gaseous giants are doomed to a life of eternal darkness. Scientists are not sure why they exist; according to the prevailing models, planets can form only around stars.
THE NEAREST PLANET. Epsilon Eridani, the closest star similar to the sun, possesses a planet that closely resembles Jupiter. William Cochran of the University of Texas and his collaborators pooled data from four planet-search groups to detect this neighboring world, which orbits 300 million miles from the star and takes about seven years to complete one circuit. Astronomers are only now accumulating enough data to identify planets that orbit their stars so slowly.
CLOAKED PLANETS. Astrophysicist Nick Gorkavyi at NASA's Goddard Space Flight Center has found a way to reveal planets hidden within the thin disks of dust surrounding many youthful stars. He devised a computer model to analyze the disks and search for whorls and clumps produced by a planet's gravitational meddling. In this way, he's found signs of three new worlds including another body, 0.2 times Jupiter's mass, 5.5 billion miles away from Epsilon Eridani, about twice Neptune's distance from the sun.
THE SMALLEST PLANET. A planet weighing in at just 0.15 the mass of Jupiter, equivalent to half the mass of Saturn, circles a star called HD 83443. It is the lightest world yet found around a sunlike star. HD 83443 also has a second, Saturn-sized planet, which bolsters the view that groupings like our solar system are not uncommon.
EARTHLIKE PLANETS. Earth-sized planets are too small and dim to show up in current searches. The Space Interferometry Mission, scheduled to launch in 2006, is designed to block out the glare of bright stars to expose life-friendly planets nearby. The proposed Kepler Mission, slated for a 2005 launch, would spot planets as minute as Mercury by watching for shadows as they cross the face of their stars the tiniest eclipses ever seen.