Milky Way may host billions of planets in 'habitable' zones: study

The Milky Way galaxy may be home to billions of planets orbiting their host stars in a "habitable zone" where life could theoretically exist, researchers said Wednesday.
      
NASA's Kepler space telescope, launched in 2009 to search for so-called "exoplanets" outside our own solar system, has already found thousands -- many of them in systems like our own with multiple planets orbiting a star.
      
Using this data, researchers from the Australian National University and the Niels Bohr Institute in Copenhagen attempted to calculate how many stars in the Milky Way could have planets in their habitable zones where liquid water could exist -- the prerequisite for life whether primitive or complex.
      
"The calculations show that billions of the stars in the Milky Way will have one to three planets in the habitable zone, where there is the potential for liquid water and where life could exist," said a statement from the Niels Bohr Institute.
      
The findings of the study were published in the scientific journal Monthly Notices of the Royal Astronomical Society.
      
The team used a new version of a 250-year-old method called the Titius-Bode law, which correctly predicted the position of Uranus before it was discovered.
      
According to the law, there is a ratio between the orbital periods of planets in a solar system.
      
Therefore, if you know how long it takes some planets to circle the star, you can calculate the orbital period of others, determine their position and find planets "missing" from the sequence.
      
"We decided to use this method to calculate the potential planetary positions in 151 planetary systems, where the Kepler satellite had found between three and six...