Kepler mission: one in five stars could host a habitable planet

Kepler candidates arranged by size.
(Credit: SETI)

NASA has announced the discovery of 833 new Kepler candidate planets, with the latest findings suggesting the number could be in the billions.

The number of counted Kepler planets — from data collected from NASA's Kepler space telescope, a telescope dedicated to seeking out Earth-like planets that are potentially habitable to humans — has risen 29 per cent since January 2013. The latest findings resulting from analysis of the data include 833 new candidate planets, bringing the total number to 3538 since the first was confirmed two years ago.

Although this is pretty exciting, the Kepler team, gathered this week at the Kepler Science Conference in California, had more news to share. New data and analysis suggests that most of the 100 billion stars in the Milky Way galaxy have at least one planet, and one in five stars is orbited by a planet up to twice the size of Earth in the star's temperate zone — that is, where the planet's surface temperature could be suitable for liquid water.

"What this means is when you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing," said UC Berkeley doctoral candidate Erik Petigura, who led the analysis.

Of course, this doesn't mean that the planets are habitable; they might not have the right atmosphere, for example.

The team examined 42,000 stars close to the size of the Sun and found 603 candidate planets. Of these planets, only 10 were Earth-size and in the temperate zone. Berkeley professor of astronomy Geoffrey Marcy said, "With tens of billions of Earth-like planets in each galaxy, our entire universe must contain billions of billions of Earth-like planets ... Until now, no one knew exactly how common potentially habitable planets were around Sun-like stars in the galaxy."

Since its 2009 launch, the Kepler telescope has been monitoring the brightness of over 150,000 stars, taking a photograph every 30 minutes. Astronomers examine the photographs for planets passing directly in front of the stars. Although Kepler's days of planet hunting came to an end when it malfunctioned in July, NASA still has over a year's worth of photographs to analyse.