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Two Near-Resonance Super-Earths Orbiting a Cool Star

24 Jun 2016, 22:00 UTC
Two Near-Resonance Super-Earths Orbiting a Cool Star
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Figure 1: Artist's impression of a rocky planet.K2-21b and K2-21c are two super-Earths in orbit around a cool host star that has 0.64 ± 0.11 times the mass and 0.60 ± 0.10 times the radius of the Sun, and an effective temperature of 4043 ± 375 K. This planetary system is located ~210 light years away. K2-21b has 1.59 ± 0.43 times the radius of Earth. Its orbital period is 9.32 days and it receives ~11.0 times the amount of flux Earth gets from the Sun, giving it an estimated equilibrium temperature of about 510 K. K2-21c has 1.92 ± 0.53 times the radius of Earth. Its orbital period is 15.50 days and it receives ~5.6 times the amount of flux Earth gets from the Sun, giving it an estimated equilibrium temperature of about 430 K.The ratio of the orbital periods of both K2-21b and K2-21c are very near to the 5:3 mean motion resonance. This means that for every 5 times K2-21b goes around its host star, K2-21c will go around close to 3 times. The sizes of K2-21b and K2-21c place them at the boundary between high-density planets with rocky compositions and low-density planets with thick gaseous envelopes. ...

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