* Astronomy

Title: Two Transiting Earth-size Planets Near Resonance Orbiting a Nearby Cool Star
Author: Erik A. Petigura, Joshua E. Schlieder, Ian J. M. Crossfield, Andrew W. Howard, Katherine M. Deck, David R. Ciardi, Evan Sinukoff, Katelyn N. Allers, William M. J. Best, Michael C. Liu, Charles A. Beichman, Howard Isaacson, Brad M. S. Hansen, Sébastien Lépine

Discoveries from the prime Kepler mission demonstrated that small planets (< 3 Earth-radii) are common outcomes of planet formation. While Kepler detected many such planets, all but a handful orbit faint, distant stars and are not amenable to precise follow up measurements. Here, we report the discovery of two small planets transiting EPIC-206011691, a bright (K = 9.4) M0 dwarf located 65±6 pc from Earth. We detected the transiting planets in photometry collected during Campaign 3 of NASA's K2 mission. Analysis of transit light curves reveals that the planets have small radii compared to their host star, 2.60 ± 0.14% and 3.15 ± 0.20%, respectively. We obtained follow up NIR spectroscopy of \epic to constrain host star properties, which imply planet sizes of 1.59 ± 0.43 Earth-radii and 1.92 ± 0.53 Earth-radii, respectively, straddling the boundary between high-density, rocky planets and low-density planets with thick gaseous envelopes. The planets have orbital periods of 9.32414 days and 15.50120 days, respectively, and have a period ratio of 1.6624, very near to the 5:3 mean motion resonance, which may be a record of the system's formation history. Transit timing variations (TTVs) due to gravitational interactions between the planets may be detectable using ground-based telescopes. Finally, this system offers a convenient laboratory for studying the bulk composition and atmospheric properties of small planets with low equilibrium temperatures.

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