Astronomers at the W.M. Keck Observatory in Hawaii have just completed an intensive five year survey of the heavens, looking at planets orbiting 166 sun-like stars within 80 light years of our own solar system. Contrary to popular theory, the study has found that the majority of planets in close orbit to their stars are some three to ten times the size of our Earth and not, as previously thought, giants with three times the mass of Jupiter. The study has also led the researchers to speculate that there could be billions of as-yet-undetected smaller planets capable of supporting life.
Using the radial velocity, or “wobble” technique, astronomers led by Andrew Howard of the University of California, Berkeley have spent the last five years looking at exoplanets of various sizes, which were in close orbit to their suns. The resulting data flies in the face of earlier theories which suggested that only giant planets inhabited the close orbital hot zone.
“We studied planets of many masses – like counting boulders, rocks and pebbles in a canyon – and found more rocks than boulders, and more pebbles than rocks,” said Howard. “Our ground-based technology can’t see the grains of sand, the Earth-size planets, but we can estimate their numbers. Earth-size planets in our galaxy are like grains of sand sprinkled on a beach – they are everywhere.”
Less than two percent of stars were found to host giant planets close in, whereas nearly 12 percent were found to have planets between three and ten times the mass of Earth. The researchers guesstimate that up to 23 percent of the sun-like stars in our galaxy host Earth-sized planets in potentially life-supporting orbit – within 0.25 astronomical units, or a quarter of the distance between our sun and the Earth.