The nearest habitable planet beyond the solar system may be relatively close to Earth, though the parent star would be a cooler and redder than the sun -- an interesting implication for any indigenous life.
Extrapolating from findings by NASA's planet-hunting Kepler Space Telescope, scientists on Wednesday said roughly six percent of so-called red dwarf stars have Earth-sized planets properly positioned around their parent stars so that liquid water could exist on their surfaces.
Water is necessary for life -- at least life as we know it.
While Kepler's prime mission is to find Earth-sized worlds around sun-like stars, its observations of red dwarf stars are providing additional food for thought, particularly because red dwarfs are by far the most common type of star in the galaxy. Typically, these stars are about one-third the size of the sun and about 1,000 times dimmer. Three out of every four stars in the galaxy are red dwarfs, adding up to about 75 billion.
At least one red dwarf has been determined to host a planet that is roughly twice the size of Earth.
"We decided that it would make sense to see if we could look at the red dwarfs in Kepler (data) whether we would find the occurrence of planets would be consistent," with the earlier study, astronomer Courtney Dressing, with the Harvard-Smithsonian Center for Astrophysics, told Discovery News.
The team looked at 95 candidate planets circling red dwarf stars observed by Kepler and found that at least 60 percent have planets smaller than Neptune. Most were not the right size or temperature to be Earth-like, but three were found to be both warm and approximately Earth-sized. Scientists, however, do not have enough information to assess if they are rocky worlds, like Earth.
Nevertheless, statistically that would mean six percent of all red dwarf stars should have a Earth-sized planet, Dressing said, adding that since 75 percent of the closest stars are red dwarfs, the nearest Earth-like world may be just 13 light-years away.
A light year is the distance that light, which moves at about 186,000 miles per second, can travel in one year -- roughly 6 trillion miles, a relative stone's throw in cosmic scales.
"If we're looking for a planet like the Earth that could possibly support life, we don't need to look as far as we thought we did initially," Dressing said.