But in this week's PNAS Online Early Edition, a team of researchers from University of California at Berkeley released a study that looks at how common Earth-size planets are around stars that are more like our sun.
The study found that for stars that more closely resemble our sun, about 22 percent, or about one in five stars, have these Earth-size planets within the habitable zone. The habitable zone includes orbits where planets receive the same amount of stellar energy from a star as the Earth receives from the sun. Earth-size planets include those that are between one and two times the size of Earth. Perhaps the most exciting prospect of the study is the finding that the closest potential Earth-like planet is only 12 lightyears away.