Ask the average person how many planets exist and many will reply “eight” or “nine,” depending on how favorably they view Pluto. A few may even toss out “10,” signifying a belief that “Planet X,” the mysterious undiscovered body believed for decades to lurk beyond Pluto, still remains undetected.
And while a few may note the existence of planets in other solar systems, it’s improbable anyone will guess billions, or even more unlikely, hundreds of billions.
But that’s what astronomers using NASA’s Kepler spacecraft have found after studying reports sent back from the observatory. The Milky Way alone contains at least 17 billion planets the size of Earth, and likely many more, researchers now believe.
About 17 percent of the 100 million stars in our galaxy have a planet about the size of Earth in a close orbit, according to astronomers, Agence France-Presse reported.
The lead author of the study estimated that there are at least 100 billion planets in total in the Milky Way.
“It’s a staggering number, if you think about it,” Jonathan Swift, a postdoctoral student at the California Institute of Technology, said in a statement. “Basically there’s one of these planets per star.”
The report does not mean that all those planets beyond our solar system, called exoplanets, could be inhabitable, but it increases the chances of finding planets similar to Earth, according to the wire service.
The Kepler space observatory, launched in 2009, is “specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets,” according to NASA.
The Kepler craft was able to detect possible exoplanets when they passed in front of their star, creating a mini-eclipse that dimmed the star slightly.
The researchers presented the analysis Monday at a meeting of the American Astronomical Society in Long Beach, Calif.
(Above: The Milky Way, seen along with the La Silla Observatory in the Atacama Desert in Chile.)