Billions of Earths?

The Kepler mission’s observing phase may have
ended, but the Kepler science team continues to work hard and deliver results.

From 2009 through early May of this year, the Kepler observatory monitored a patch of sky in the constellation Cygnus and carefully measured the amount of light coming from more than 100,000 stars in that region. Whenever a planet orbiting one of these distant suns passed between Kepler and its parent star, we could see a fraction of the light from the star blocked by the planet. Bigger planets blocked more light, and planets close to their star passed more frequently, so unsurprisingly, large and hot planets dominated the early results from the first two years of observation.

But yesterday, scientists discussed data accumulated during the third year of the mission with some surprising evidence coming to light. They report data revealing many more planets and, astonishingly, the data also demonstrate just how common Earth-like planets are within the Milky Way.

During a press conference yesterday, Kepler added 835 more candidates bringing the total number of possible planets to over 3,500. Remember, planets are candidates until confirmed, and with a success rate of about 90% of candidates later confirmed as planets, they appear to be commonplace within our galaxy.

But wait, there’s more! UC Berkeley researchers, publishing yesterday in the Proceedings of the National Academy of Sciences, state that perhaps one in five stars has a small rocky planet within the habitable zone of the star!

The fraction seems impressive enough but becomes even more amazing when you multiply it out based on the total number of stars in our Milky Way. There are approximately 200 billion stars that make up our galaxy, so if one in five of these stars has a potential Earth going around it, there could be 40 billion possible planets supporting life!

Many scientists are still debating exactly what makes a planet habitable, but when possible sites are this numerous, it is easy to imagine almost any configuration of the many varying factors exists somewhere out there in the Universe. With so many potential Earths, the possibility of finding another planet like the one we all know and love seems within reach.

(A video and press release of the Earth-like planets discovery is available here.)

Josh Roberts is a program presenter and astronomer at the California Academy of Sciences. He also contributes content to Morrison Planetarium productions.

Image credit: NASA Ames/JPL-Caltech/Tim Pyle