PURPLE SUNSHINE?: Exoplanet MOA-192 b is bathed in the Mace Windu lightsaber–like glow radiated by its star in this artist's impression. Where will this world place in the top 10? Image: NASA's Exoplanet Exploration Program
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Hoth. Coruscant. Endor. These names will ring familiar to fans of that galaxy far, far away—the setting for the Star Wars movies, including the new animated feature Star Wars: The Clone Wars. Now what about V391 Peg b? GJ 3021 b? WASP-15 b? If you guessed Star Wars droids, you're wrong. They're the names of actual planets found around other stars in our own Milky Way Galaxy.
Slowly but surely researchers are learning that our stellar neighborhood is filled with extrasolar planets, better known as exoplanets. Many of them are just as, if not far more, exotic as anything in the Star Wars saga. And someday they may have names that are equally memorable.
Scientists have found over 300 exoplanets since 1991, and they hope to find a great deal more. David Bennett, an astrophysicist at the University of Notre Dame and a dedicated planet hunter, says that current estimates peg the number of stars bearing planets at about 30 percent, though he thinks this figure is closer to 50 percent, as researchers believe that current technology is not yet up to the task of spotting certain categories of planets such as small, Earth-size ones. With 100 billion stars populating the Milky Way galaxy, that means some 50 billion planetary systems may await discovery, many of which may hold multiple planets resembling our eight-planet configuration. "We think there are actually more planets out there than stars," says Bennett.
Unlike the livable worlds in Star Wars, none of the exoplanets discovered thus far are sufficiently Earth-like in either size or distance from their star to be deemed good candidates for life. The vast majority of known exoplanets are so-called "hot Jupiters" (or "hot Yavins," in Star Wars parlance): large, gaseous bodies orbiting close to their host stars. The apparent preponderance of inhospitable places stems from the limitations of currently available detection methods. Ground-based telescopes gather indirect evidence of an exoplanet's presence around a star, in the form of regular variations of starlight, and smallish planets like Earth have tiny, hard-to-discern effects on their massive hosts.
But NASA and other space organizations have launched or are planning new missions to better identify Earth-like planets. A European satellite called COROT (COnvection ROtation and planetary Transits) has been successfully hunting exoplanets since 2007, and early next year NASA plans to power up the Kepler space telescope. This device will spy on 100,000 stars simultaneously from solar orbit over four years to try and suss out the miniscule signatures of Earth-like planets.
For now, we must rely on artist's impressions to get a sense of what all these extrasolar worlds may look like. But getting actual pictures of exoplanets should become possible in the coming years. The New Worlds Observer project, tentatively scheduled to start up late next decade, will use a flower-shaped "starshade" to block out a star's overwhelming, planet-obscuring glare. Scientists then hope to snap direct images of exoplanets and study their atmospheres for telltale signs of life such as oxygen and water vapor. "The New Worlds Observer will allow us to look for evidence of oceans and even continents on exoplanets whose stars are close to Earth," says Webster Cash, the developer of the starshade and an astrophysicist and planetary scientist at the University of Colorado at Boulder.