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To determine exactly why Kepler-107c is so dense, first the researchers considered what they already knew. Previous research has shown that intense stellar radiation can strip the atmosphere from a planet that sits too near its host star. But if the innermost planet lost its lighter atmospheric elements, it should be more dense than its twin, not less. According to the study, this would "make the more-irradiated and less-massive planet Kepler-107b denser than Kepler-107c," which is clearly not the case. However, there is another way that a planet can lose a lot of mass: by getting smacked with another planet....

Explanation: Framing a bright emission region this telescopic view looks out along the plane of our Milky Way Galaxy toward the nebula rich constellation Cygnus the Swan. Popularly called the Tulip Nebula the glowing cloud of interstellar gas and dust is also found in the 1959 catalog by astronomer Stewart Sharpless as Sh2-101. About 8,000 light-years distant and 70 light-years across the complex and beautiful nebula blossoms at the center of this composite image. Red, green, and blue hues map emission from ionized sulfur, hydrogen, and oxygen atoms. Ultraviolet radiation from young, energetic stars at the edge of the Cygnus...