Data from Kepler space telescope indicates Earth-like planets are right next door

Artist’s conception of a hypothetical habitable planet with two moons orbiting a red dwarf star.
Credit: David A. Aguilar (CfA)

Using publicly available data from NASA’s Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) have found that six percent of red dwarf stars have habitable, Earth-sized planets. Since red dwarfs are the most common stars in our galaxy, the closest Earth-like planet could be just 13 light-years away.

“We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted,” said Harvard astronomer and lead author Courtney Dressing (CfA).

Due to their low luminosity, individual red dwarfs cannot easily be observed. From Earth, not one is visible to the naked eye. Launched in March 2009, the Kepler spacecraft identifies planet candidates by repeatedly measuring the tiny change in brightness of more than 150,000 target stars to detect when a planet transits the face of the star. The size of the planet can be derived from these periodic dips in brightness.

Dressing culled the Kepler catalog to identify all the red dwarfs and then reanalyzed those stars to calculate more accurate sizes and temperatures. She found that almost all of those stars were smaller and cooler than prior estimates.

Dressing identified 95 planetary candidates orbiting red dwarf stars. This implied that at least 60 percent of such stars have planets smaller than Neptune. However, most weren’t quite the right size or temperature to be considered truly Earth-like. Three planetary candidates were both warm and approximately Earth-sized. Statistically, this means that six percent of all red dwarf stars should have an Earth-like planet.

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said co-author David Charbonneau (CfA). “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

Our Sun is surrounded by a swarm of red dwarf stars. About 75 percent of the closest stars are red dwarfs. Since 6 percent of those should host habitable planets, the closest Earth-like world is likely to be just 13 light-years away.

The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5,700 and 5,900 degrees Fahrenheit. (For comparison, our Sun’s surface is 10,000 degrees F.)

In order to produce a system with enough sensitivity to detect the smaller, Earth-like planets as they pass in front of their host stars, a very high reflectance coating was required for the Kepler primary mirror. A protected and enhanced silver coating was selected to satisfy this need. The protected silver coating formulation was developed at Lawrence Livermore National Laboratory (LLNL) and applied by Surface Optics Corporation using an ion assisted evaporation process.

In April 2012, NASA awarded Kepler an extended mission to
continue searching for earth-like habitable planets, through as
late as 2016.
For more information about the discovery, see the full press release.