The research, by Charles Lada of the Harvard-Smithsonian Center for Astrophysics, also suggests that because planets tend to form more easily around single stars, planets may be much more common in the galaxy than previously thought.

"The population of the galaxy is really dominated by these very faint small stars," Lada told SpaceDaily.com.

In all, he explained, about 80 percent out of the estimated 100 billion stars in the Milky Way are red dwarfs, ranging in size from about one-half the mass of the Sun to as small as one-tenth the mass of our star.

"It depends on how you count," Lada said. "If you have 80 billion of what we call primaries, and you have 25 percent in multiple stars, then about 20 billion red dwarfs are in these binary systems, but another 60 billion are single. It's not often appreciated how numerous they are, but they are the most numerous of all stars."

The research, which has been submitted to The Astrophysical Journal Letters, also suggests that many more planets in the galaxy could be Earth-like than previously thought.

"Whether planets around these stars could be Earth-like would depend on orbital distance," Lada said. "There have been extensive studies and it turns out these planets would have to be pretty close to their stars, although it would depend on the mass of the stars."

He said an Earth-like planet circling a red dwarf would have to be so close it would be tidally locked, like the Moon to Earth, and show only one face to its parent star. "One side of the planet would always face the red dwarf and be in perpetual warmth, and the other side would always face away and be much, much colder," he explained. "So that's an interesting twist to what things would be like on such a planet, but it's certainly possible for the right conditions to exist that would be similar to Earth."

Possibly the most interesting aspect of red dwarfs is their age. "Red dwarfs can live maybe a trillion years or so," Lada said. "Since the beginning of the universe, the red dwarfs that have formed, none of them have died."

That fact attaches two extremely interesting possibilities to these little bodies. "The original ones that formed are still there. So the big advantage of these stars is there is plenty of time for life to evolve, plenty of time for civilizations to develop, if indeed the conditions can be right."

Also, Lada said, when the Sun eventually dies, a nearby red dwarf might serve as an ark for humanity's descendants. "If we're still around, we probably would want to look to resettling around a red dwarf because that thing is going to be stable for eons."

He said the closest red dwarf to Earth is Proxima Centauri, only 4.22 light-years away -- although it is part of a triple star system . "There are plenty nearby us," he added.

This research has been submitted to The Astrophysical Journal Letters for publication and is available online at http://arxiv.org/abs/astro-ph/0601375

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