Up to 80 percent of the stars in the galaxy are thought to be red dwarfs. If 6 percent have an Earth-like planet, that means the galaxy could host between 9.6 billion and 19.2 billion potentially-habitable Earths around these stars alone.
The results reinforce a growing recognition that our solar system, with its larger, hotter star, "is quite rare," says John Johnson, an astronomer at the California Institute of Technology in Pasadena who studies extrasolar planets. "It's quite remarkable that the vast majority of habitable planets throughout the galaxy are likely around these red dwarfs."
The results also "highlight just how quickly the field of extrasolar planets is blooming," he adds.
In 2000, astronomers had only detected 33 planets, all gas giants the size of Saturn or larger. They have now found 3,300, when Kepler's planet candidates are included.
The new study, conducted by Harvard University graduate student Courtney Dressing and astronomer David Charbonneau at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., casts a new eye on the red dwarfs previously cataloged by the Kepler team.