The hunt for planets around other stars just got easier. Alice Quillen of the University of Rochester and undergraduate Stephen Thorndike of Alfred University, also in New York, have found a way to detect worlds too small or slow-orbiting to show up in current surveys. This method has revealed what may be a Neptune-size body circling Epsilon Eridani, one of the closest sunlike stars.
Astronomers have identified more than 100 planets orbiting stars outside our solar system, primarily by monitoring the way a planet's gravity tugs its star back and forth. That technique most readily picks up Jupiter-size planets in fast, Mercury-like orbits, objects unlike anything in our solar system. A newer approach, looking for the shadow of a planet passing in front of its star, has similar limitations.
Quillen and Thorndike instead study subtle gravitational disturbances in the dust rings that surround many stars less than a billion years old. As a test, the researchers observed infrared emissions from the faint dust around Epsilon Eridani and compared them with computer simulations of clumping patterns. Their results indicate a possible planet approximately the mass of Neptune—the smallest yet seen around a sunlike star—orbiting every 280 years. That period is similar to the 164-year orbit of the real Neptune. "We were totally surprised," Quillen says.
Previous studies have revealed a Jupiter-mass planet in a roughly Jupiter-like orbit around Epsilon Eridani. If the new planet checks out, Epsilon Eridani starts to look a lot like our solar system. Quillen wants to use NASA's new Space Infrared Telescope Facility to get a clearer view of the dust ring. Earth-like planets, however, remain beyond the limits of today's searches.