Study: Billions of Earth-Size Planets in Milky Way
Our Milky Way is home to at least 17 billion planets that are similar in size to Earth, a new estimate suggests. That’s more than two Earth-size planets for every person on the globe.
Just how many are located in the sweet spot where water could exist is "simply too early to call," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics, who presented his work at an astronomy meeting Monday.
It’s the first reliable tally of the number of worlds outside the solar system that are the size of Earth, but the hunt for our twin is far from over.
Despite the explosion of exoplanet discoveries in recent years, one find remains elusive: A planet that’s not only the right size but also in the so-called Goldilocks zone where it’s not too hot or too cold for water to be in liquid form on the surface.
The sheer number of Earth-size planets gives astronomers a starting point to narrow down which ones are in the habitable zone.
Fressin and his team came up with their figure by conducting a fresh analysis of data collected by NASA’s Kepler spacecraft, which was launched in 2009 to track down other Earths. They estimated at least one in six stars in the galaxy hosts a planet the size of ours, translating to at least 17 billion Earth-size worlds.