Last year the discovery of Kepler-16b, a planet orbiting two stars, was announced. Now the Kepler Space Telescope discovered that in the binary system Kepler-47 there are at least two planets, one of which is within the system’s habitable zone, the area in which water can be in its liquid state on the surface of the planet in conditions similar to those of the Earth.
The Kepler-47 system is about 4,900 light-years from Earth in the constellation Cygnus. One of the two stars is similar to the Sun and has 84% of its brightness, the other is a red dwarf star about one-third the size of the Sun and only less than one-hundredth of its brightness.
The planet Kepler-47b is the largest, with a radius about three times the Earth and an orbital period less than 50 days. Probably its surface is sweltering and due to the presence of methane it may be covered by thick clouds like Venus.
The planet Kepler-47c is probably a gas giant slightly larger than Neptune with an orbital period of 303 days. It’s within the habitable zone of its system but if it really is a gas giant there can be no life similar to that of Earth.
This isn’t the first time a planet orbiting two stars was discovered but in the Kepler-47 system there are at least two of them and that’s the really interesting element. So far, there were serious doubts about the possibility that a system of circumbinary planets, which are planets that orbit two stars, could form. The doubts came from the idea that the instability caused by the combination of the gravity of the two stars interferes with the formation of planets.
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In our solar system there’s Jupiter, near which there’s an asteroid belt because its gravity prevented the formation of a planet. Scientists’ idea was that the presence of a second star in a system caused even more interference.
We don’t know if Kepler-47 is an exceptional system. The Kepler Space Telescope has already observed more than 150,000 stars and there are still a lot of data to analyze. Surely they’ll find more planets, if they were found more circumbinary systems of this type the current theories on the formation of planets would need to be revised significantly, at least concerning binary systems.
