Our Milky Way galaxy holds a minimum of 100 billion planets

There could be one planet for every star on average, study concludes

A study out today says our Milky Way galaxy holds at least 100 billion planets  -- a minimum of one planet for every star on average. This finding means that there could be  a minimum of 1,500 planets within 50 light-years of Earth.

The results are based on observations taken over six years by the Probing Lensing Anomalies NETwork (PLANET) collaboration.  The study concludes that there are far more Earth-sized planets than big Jupiter-sized worlds, according to Kailash Sahu, of the Space Telescope Science Institute who is part of an international team that includes astronomers from the European Southern Observatory that reported the study's findings this week.

More: 10 game-changing space galaxy discoveries

As Sahu explained, the team's conclusions are gleaned from a planet search technique called "microlensing." The technique takes advantage of the random motions of stars, which are generally too small to be noticed. If one star passes precisely in front of another star, the gravity of the foreground star bends the light from the background star. This means that the foreground star acts like a giant lens amplifying the light from the background star. A planetary companion around the foreground star can produce additional brightening of the background star. This additional brightening reveals the planet, which is otherwise too faint to be seen by telescopes.  Using the microlensing technique, astronomers can determine a planet's mass. This method, however, does not reveal any clues about the world's composition, Sahu said.

"We have searched for evidence for exoplanets in six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our galaxy. We also found that lighter planets, such as super-Earths or cool Neptunes, must be more common than heavier ones," said Arnaud Cassan of the Institut dʼAstrophysique de Paris, lead author of the study that appeared in Nature this week.  

Follow Michael Cooney on Twitter: nwwlayer8  and on Facebook

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