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.

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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.

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"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.

When it's young, a red dwarf star frequently erupts with strong ultraviolet flares as shown in this artist's conception.David A. Aguilar

It will take more sensitive telescopes than what exist today to uncover telltale chemical signs of life, if any exist, but that doesn't stop scientists from imagining.

Plants, for example, may be very different on a planet that evolved around a red dwarf star, rather than a yellow star like the sun. Not only would the wavelengths of light be redder, but the planets would be exposed to more radiation over the long haul, conditions that might make for dark brown and black plants, rather than green, said astronomer Lisa Kaltenegger, with the Max-Planck Institute for Astrophysics in Germany.

"The other question is, this is speculative of course, but would plant life if it came along, also use chlorophyll, or would they develop something completely different?" Kaltenegger told Discovery News. "Plants on Earth are extremely evolved to use the energy from the sun. You could envision different schemes that do something similar."

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Taking the speculation a bit farther, Kaltenegger said she wouldn't expect much difference in any microbial life on red dwarf planets.

"We don't know if life actually develops, but one big difference is the amount of radiation (on red dwarf planets.) The argument people make is that it would be really bad for life on the surface. But if you evolve for that, you shouldn't have any problem," she said.

Dressing's findings, which were announced at a press conference on Wednesday, are expected to be published in an upcoming edition of The Astrophysical Journal.