In amongst archived data from the Kepler mission, a team of German and American researchers has identified an Earth-like planetary candidate, KOI-456.04, situated within its host star’s habitable zone. What sets this discovery apart from other known Earth-like exoplanets is that its star, Kepler-160, bears a striking resemblance to our Sun. Although the planet’s presence is yet to be confirmed, this exoplanet-star pairing could be one of the closest matches to the Earth-Sun system that we’ve found so far.
“KOI-456.01 is relatively large compared to many other planets that are considered potentially habitable,” Dr René Heller of Max Planck Institute for Solar System Research, Germany, and lead author of the research, said in a statement. “But it’s the combination of this less-than-double the size of the Earth planet and its solar type host star that make it so special and familiar.”
Located over 3,000 light-years away from Earth, the star Kepler-160 is around 1.1 times the size of the Sun and has a surface temperature of 5200˚C, only 300 degrees less than Sun. The star is already known to have two exoplanets – Kepler-160 b, a rocky super-Earth, and Kepler-160 c, a Neptune-like gas giant – but the duo’s orbits are very close to the star, and are thought to be too hot to be habitable. Yet the possibility of a third planet, hinted at by variations in Kepler-160 c’s orbital period, tempted astronomers to take another look at the planetary system.
Both previous planets were discovered by searching for periodic dips in Kepler-160’s brightness that indicates a transiting object. However, these temporary dimmings are hard to detect from smaller exoplanets, therefore Heller and his team created a new search algorithm that could more accurately pinpoint the presence of these planets.
Lo and behold their improved approach found KOI-456.04. With an incredibly similar orbital period to Earth of 378 days, KOI-456.04 lies at a distance from Kepler-160 conducive to the existence of liquid water. But further analysis showed that this was not the culprit of Kepler-160 c’s distortions. There was in fact another non-transiting planet that was responsible, Kepler-160 d.
“Our analysis suggests that Kepler-160 is orbited not by two but by a total of four planets,” Heller said.
As described in their paper, published in Astronomy and Astrophysics, indirectly confirmed Kepler-160 d has a mass between 1 and 100 Earth masses, and an orbital period from 7 to 50 days. However, this planet has fallen into the shadows of the more intriguing combination of the Earth-like KOI-456.04 orbiting within the habitable zone of the Sun-like Kepler-160.
Most Sun-like stars discovered by Kepler have a Neptune-sized planet in a much closer orbit, too hot to be habitable (like Kepler-160 c). On the flip-side other Earth-sized planets that have been found in a star’s habitable zone, have tended to have red dwarfs as hosts – small, faint stars with a low surface temperature. These stars also differ from the Sun, in that they emit mostly infra-red radiation, rather than the visible light that we receive from the Sun. For this reason, amongst many others, the habitability of planets around red dwarfs is heavily debated.
However, these concerns are not shared for Kepler-160, as not only does it radiate visible light, but it does so at a luminosity similar to the Sun. Meaning that newly found KOI-456.04 receives about 93 percent of the amount of sunlight that we experience on Earth. The researchers suggest that if KOI-456.04 were to have an inert atmosphere with a mild Earth-like greenhouse effect its surface temperature would be around 5˚C, roughly 10˚C less than Earth’s average temperature.
Boasting an 85 percent chance of planetary possibility, KOI-456.04 has not yet reached the 99 percent benchmark needed for full confirmation. Astronomers suspect that they may need to wait for future space missions, such as ESA’s PLATO spacecraft before they get complete validation.