An international research group led by René Heller from the Max Planck Institute for Solar System Research in Göttingen, Germany, claims to have found a star-exoplanet pair closely resembling the Sun-Earth system, based on their statistical data analysis. This distant solar system circles the star Kepler-160, a G dwarf star like our Sun located about 3,000 light years from Earth.
Heller and colleagues used a novel method to make their discovery. Rather than detecting step-wise jumps in the star’s light curve, they created a detailed physical model of Kepler-160’s brightness variations. This new technique revealed a fourth, previously unknown planet circling the star.
The new planet has been given the prelimimary designation KOI 456.04. It’s projected to be in the habitable zone—an orbit that would allow the presence of liquid water on its surface. The planet completes an orbit around its host star in 378 days, very close to Earth’s year of 365.25 days. KOI 456.04 is a bit less than twice the size of our own planet.
Does this mean it might be hot like Venus (which also is close to Earth-size)? The surface temperature of the host star is about 300oC less than our Sun, and if the planet is not too massive, and has a greenhouse effect not as stong as Earth’s, then surface temperatures on the newly discovered planet may still be rather benign. Perhaps it could be tropical?
This study is very significant, because nearly all the small exoplanets (less than twice the size of Earth) discovered to date are in orbit around M dwarf stars—by far the most common variety in the galaxy. These stars, also called Red Dwarfs, emit high-energy flares early in their life cycle, and the habitable zone is so close to the star that many of the potentially habitable planets are likely to be tidally “locked,” which means they would have huge temperature variations between the side of the planet facing the star and the other side. More luminous K or G dwarf stars (like our Sun) are therefore more suitable for hosting life-bearing planets.
While some of the properties of Kepler-160 and KOI 456.04 make them similar to the Sun and Earth, the overall system is actually quite different. Two of the three inner planets are substantially bigger than Earth, and one is as large as Neptune. It’s even possible that KOI 456.04 is a “small Neptune” rather than a big Earth. And there’s a 15 percent chance that its identification as a planet turns out to be a false positive (hence the preliminary KOI designation).
So the discovery by Heller and colleagues has to be confirmed, either with ground-based telescopes or with the PLATO space telescope due to launch in 2026. But even though there are still a lot of “ifs,” it shows that we are (slowly) edging closer to finding an Earth 2.0 circling a Sun 2.0.