#Milky Way may host 6 billion Earth-like worlds, study says

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Milky way over stone lions, Heihe City, Heilongjiang Province, China.
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Early this week a study made big headlines across the internet by claiming that there may be as many as 36 intelligent alien races within the Milky Way galaxy alone. It was an incredibly bold claim, but it was based on the likelihood of life developing on planets similar to Earth. So, just how many Earth-like worlds are there out there in our home galaxy? A totally separate study has sprung up just in time to answer that question.

In a new paper published in The Astronomical Journal, researchers using data from the Kepler Space Telescope crunched the numbers and ventured a truly mind-boggling guess. Based on what we know about Earth’s place in our solar system and the formation of rocky worlds in the so-called habitable zone of any given star, the researchers believe there may be as many as six billion Earth-like worlds in the Milky Way. Wow.

The calculation comes down to some pretty simple math, courtesy of the Kepler telescope’s observations. Put simply, the odds of an Earth-like planet existing around a given star is roughly 18% or roughly one out of every five stars of a type that would be suitable for life. Multiply that number by the number of those stars believed to exist in our entire galaxy and you get the lofty figure of six billion.

“My calculations place an upper limit of 0.18 Earth-like planets per G-type star,” Michelle Kunimoto, co-author of the research, said in a statement. “Estimating how common different kinds of planets are around different stars can provide important constraints on planet formation and evolution theories, and help optimize future missions dedicated to finding exoplanets.”

Instruments like Kepler are well equipped to discover planets orbiting closely around their stars, but they’re less adept at detecting planets orbiting at a greater distance. The further a planet is from its star, the less likely Kepler will be to detect it, and the habitable zone of stars like our Sun is far enough away that it poses a challenge for the discovery of Earth-like worlds.

In the future, new technologies and more advanced instruments may be better able to spot planets orbiting at comfortable distances from their host stars. At that point, we may need an updated estimate of the number of Earth-alikes that are lurking out there in the cosmos. For now, however, six billion seems like a pretty exciting number, and helps put the search for alien civilizations into a new perspective.