4.5 billion ‘alien Earths’ may reside in Milky Way

How many planets are in the Milky Way?

By Daniel Carrington, The Space Reporter
Thursday, February 07, 2013

4.5 billion ‘alien Earths’ may reside in Milky Way

There are a lot of Earth-like planets wandering around the Milky Way galaxy, according to a study published by a team of Harvard University astronomers.

According to astronomers, Earth-like planets may litter the cosmos, including our own Milky Way galaxy. The report, led by Harvard University graduate student Courtney Dressin, concludes that upwards of 4.5 billion Earth-like planets may reside within our own galaxy, the highest estimate to date. When matched against the number of stars in the galaxy, the number of planets may exceed 17 billion.

The study, which was conducted by the Harvard-Smithsonian Center for Astrophysics team, estimates that nearly six percent of the 75 billion red dwarf stars within the Milky Way galaxy have Earth-like planets. Using data collected by NASA, the team examined 95 planet candidates orbiting 64 red dwarf stars. While a large portion of the planets did not meet the definition of habitable, three exoplanets were both temperate and smaller than twice the size of Earth.

Among the study’s more interesting conclusions, is the fact that a handful of Earth-like planets may reside within traveling range. Astronomers say the odds are good that at least one Earth-like planet resides just 13 light-years – 77 trillion miles – away. The age of the stars the planets orbit also indicate that some of the planets may be far older than Earth; one of these target planets could be 12 billion years old, the scientists said.

While the study estimate is likely to draw interest, the fact that many of the red dwarf stars do not burn as hot as regular stars, such as our sun, means the planets in question orbit much closer to their star. The resulting difference in orbits could make identifying such planets far more difficult for astronomers.

The data, collected by NASA’s Kepler Space Telescope, is the latest twist in the ever-changing quest to spot the first true Earth-like planet. Recently, a number of astronomers have put forth estimates for the number of Earth-like planet thought to exist within the universe and the Milky Way. Estimates range from trillions of planets (throughout the universe) to billions of planets within various galaxies.

While the study’s findings are drawing interest from the astronomy community, researchers warned against reading too much into the figures. The team noted that even if an Earth-like planet exists, it does not necessary mean extraterrestrial life thrives. In addition, the distance separating Earth-like planets from our own planet Earth remain well outside the capabilities of modern technology.

That said, the implications of the study could bode well for future missions to discover life outside of our planet. The Kepler catalog of exoplanets lists upwards of 2,000 planets, 800 of which have been identified by astronomers all across the world.

The results are slated to appear in Astrophysical Journal.


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