Billions of Earth-like alien planets likely reside in our Milky Way galaxy, and the nearest such world may be just a stone's throw away in the cosmic scheme of things, a new study reports.
Astronomers have calculated that 6 percent of the galaxy's 75 billion or so red dwarfs — stars smaller and dimmer than the Earth's own sun — probably host habitable, roughly Earth-size planets. That works out to at least 4.5 billion such "alien Earths," the closest of which might be found a mere dozen light-years away, researchers said.
"We thought we would have to search vast distances to find an Earth-like planet," study lead author Courtney Dressing, of the Harvard-Smithsonian Center for Astrophysics (CfA), said in a statement. "Now we realize another Earth is probably in our own backyard, waiting to be spotted."
Dressing and her team analyzed data gathered by NASA's prolific Kepler space telescope, which is staring continuously at more than 150,000 target stars. Kepler spots alien planets by flagging the tiny brightness dips caused when the planets transit, or cross the face of, their stars from the instrument's perspective.
Kepler has detected 2,740 exoplanet candidates since its March 2009 launch. Follow-up observations have confirmed only 105 of these possibilities to date, but mission scientists estimate that more than 90 percent will end up being the real deal.
In the new study, Dressing and her colleagues re-analyzed the red dwarfs in Kepler's field of view and found that nearly all are smaller and cooler than previously thought.
This new information bears strongly on the search for Earth-like alien planets, since roughly 75 percent of the galaxy's 100 billion or so stars are red dwarfs.