Milky Way Galaxy May Hold 4.5 Billion 'Alien Earths'

The universe can be a lonely place, but you are not alone. And neither is Earth, quite possibly. The Milk Way is home to billions of Earth-like, potentially habitable planets that may support life, according to a new study from the Harvard-Smithsonian Center for Astrophysics.

Examining data from NASA's Kepler space telescope in orbit, scientists found that 6 percent of the roughly 75 billion red dwarf stars in our galaxy likely have such planets. That works out to about 4.5 billion other possible Earth-like planets drifting through the cosmos, the closest of which may just be about 13 light years away, "down the street" by space standards, ABC News reported. The distance may sound great, but it's actually much closer than it appears, even nearer to earth than most stars like our planet's sun.

"We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted," said Courtney Dressing, an astronomer at the Harvard-Smithsonian Center.

The Kepler space telescope has detected 2,740 exoplanet candidates since it first began observing the skies in March 2009, according to Fox News. Exoplanets are planets outside of our solar system. Most of the exoplanets discovered don't resemble Earth, but rather have characteristics more similar to gas giants like Neptune or Jupiter, according to Space.com.

Since astronomers began taking another look at those candidate planets, observations have only confirmed 105 of the planets to date, but scientists predict more than 90 percent will eventually be confirmed as Earth-like planets.

As Dressing and her colleagues re-analyzed the red dwarfs in Kepler's field of vision, they discovered that almost all are smaller and cooler than researchers believed in the past. The findings suggest the galaxy could possibly contain more Earth-like planets than ever previously thought, as about 75 percent of the galaxy's roughly 100 billion stars are red dwarfs.

"We now know the rate of occurrence of habitable planets around the most common stars in our galaxy. That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought," commented study co-author David Charbonneau.

Red dwarfs are smaller, less bright, and older than our sun, but a planet orbiting close to such a star could still be warm enough to support liquid water, according to ABC News. In the new study, scientists were able to find three possible planets spotted by Kepler, with one about 90 percent the size of Earth that orbits its red sun in about 20 of our planet's days.

Of course, just what the planets are like beyond that remains a mystery. The Kepler space telescope is only capable of showing whether far off stars have objects periodically moving in front of them. However, that's still enough information to allow scientists to calculate and predict the mass and orbit of potential planets.

Estimates put our galaxy's star count somewhere between 200 and 400 billion, and ours is likely a fairly typical galaxy, according to Fox News. Thus, the new predictions suggest our universe is overflowing with planets like ours.

"The knowledge that another an Earth-like planet might be so close is incredibly exciting and bodes well for the next generation of missions designed to detect nearby Earth-like planets," she added. "Once we find nearby Earth-like planets, astronomers are eager to study them in detail with the James Webb Space Telescope and proposed extremely large ground-based telescopes like the Giant Magellan Telescope."

Because red dwarfs are much older than stars like our sun - which scientists estimate first flipped the light switch 3.8 billion years ago - astronomers say it's possible that some planets in these red dwarf habitable zones may contain life that's been kicking around the universe even longer than we have on Earth.

"We might find an Earth that's 10 billion years old," Charbonneau said.