Further evidence that stars commonly have planets has emerged from a study that found signs of large bodies orbiting every one of the three nearby stars examined.
"Our study is just one more nail in the coffin of any idea that planets are rare," said Dana Backman of Kitt Peak National Observatory, who found the evidence in collaboration with Frederick Gillett, now with the National Aeronautics and Space Administration. They reported their findings earlier this month at a meeting of the American Astronomical Society in Pasadena, Calif.
The two astronomers discovered that dust clouds surrounding the stars contain cleared regions, as if planet-sized objects were orbiting each star and sweeping up particles. The cleared regions extended about as far from the star as planets extend from our sun.
The scientists' evidence is in the form of infrared radiation from the region around each star studied. Starlight, comparable to sunlight, warms objects orbiting the star. The energy is then reradiated from the object as infrared radiation that can be detected by special infrared-detecting telescopes on Earth.
The amount of infrared from any spot in the sky depends on the surface area available to emit the radiation. Therefore, a dust cloud would give off far more radiation than the same mass condensed into a planet. Given the equipment used, the astronomers could not detect a planet directly but could see a disc-shaped, hollowed region within the larger dust cloud.
The researchers said the smallest objects that could have swept dust from cleared regions of the observed size would have to be at least the size of Earth.
A year ago, the same astronomers reported that 20 percent of the 134 stars they examined were surrounded by detectable dust clouds. That finding led many astronomers to speculate that the clouds were planetary systems in the process of forming.
The new observations, on only three of the dust clouds, showed all to have cleared-out regions. With such odds, the Kitt Peak astronomers said all of the dust clouds may hold planets.
They also noted that our solar system may be surrounded by a dust cloud that, for various reasons, would be undetectable from Earth.