Astronomers have found a planet like Earth orbiting a star like the sun

The discovery of the exoplanet KOI-456.04 orbiting the star Kepler-160 suggests we should more aggressively look for habitable planets around sun-like stars.

Three thousand light-years from Earth sits Kepler 160, a sun-like star that’s already thought to have three planets in its system. Now researchers think they’ve found a fourth. Planet KOI-456.04, as it’s called, appears similar to Earth in size and orbit, raising new hopes we’ve found perhaps the best candidate yet for a habitable exoplanet that resembles our home world. The new findings bolster the case for devoting more time to looking for planets orbiting stars like Kepler-160 and our sun, where there’s a better chance a planet can receive the kind of illumination that’s amenable to life.

Most exoplanet discoveries so far have been made around red dwarf stars. This isn’t totally unexpected; red dwarfs are the most common type of star out there. And our main method for finding exoplanets involves looking for stellar transits—periodic dips in a star’s brightness as an orbiting object passes in front of it. This is much easier to do for dimmer stars like red dwarfs, which are smaller than our sun and emit more of their energy as infrared radiation. The highest-profile discovery of this type is near our closest neighboring star, Proxima Centauri—a red dwarf with a potentially habitable planet called Proxima b (whose existence was, incidentally, confirmed in a new study published this week).

Data on the new exoplanet orbiting Kepler 160, published in Astronomy and Astrophysics on Thursday, points to a different situation entirely. From what researchers can tell, KOI 456.04 looks to be less than twice the size of Earth and is apparently orbiting Kepler-160 at about the same distance from Earth to the sun (one complete orbit is 378 days). Perhaps most important, it receives about 93% as much light as Earth gets from the sun.

This is critical, because one of the biggest obstacles to habitability around red dwarf stars is they can emit a lot of high-energy flares and radiation that could fry a planet and any life on it. By contrast, stars like the sun—and Kepler-160, in theory—are more stable and suitable for the evolution of life.

The authors found KOI-456.04 by reanalyzing old data collected by NASA’s Kepler mission. The team employed two new algorithms to analyze the stellar brightness observed from Kepler-160. The algorithms were designed to look at dimming patterns on a more granular and gradual level, rather than seeking the abrupt dips and jumps that had previously been used to identify exoplanets in the star system. 

Right now the researchers say it’s 85% probable KOI-456.04 is an actual planet. But it could still be an artifact of Kepler’s instruments or the new analysis—an object needs to pass a threshold of 99% to be a certified exoplanet. Getting that level of certainty will require direct observations. The instruments on NASA’s upcoming James Webb Space Telescope are expected to be up to the task, as are those on ESA’s PLATO space telescope, due to launch in 2026.