Two Transiting Earth-size Planets Near Resonance Orbiting a Nearby Cool Star
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, S\'ebastien L\'epine

TL;DR
This paper reports the discovery of two small, near-resonant transiting planets around a bright M0 dwarf star, providing valuable insights into their composition, orbital dynamics, and potential for follow-up studies.
Contribution
First detection of two small transiting planets near resonance around a bright, nearby star, enabling detailed follow-up observations and analysis.
Findings
Planets have radii of approximately 1.6 and 1.9 Earth-radii.
Orbital periods are 9.3 and 15.5 days, near 5:3 resonance.
Potential for transit timing variation detection.
Abstract
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 K2-21, a bright (K = 9.4) M0 dwarf located 656 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 K2-21 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…
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