Two transiting earth-size planets near resonance orbiting a nearby cool star

Petigura, Erik A. and Schlieder, Joshua E. and Crossfield, Ian J M and Howard, Andrew W. and Deck, Katherine M. and Ciardi, David R. and Sinukoff, Evan and Allers, Katelyn N. and Best, William M. J. and Liu, Michael C. and Beichman, Charles A. and Isaacson, Howard and Hansen, Brad M. S. and Lepine, Sebastien (2015) Two transiting earth-size planets near resonance orbiting a nearby cool star. The Astrophysical Journal, 811 (2). pp. 102-110. ISSN 0004-637X

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Discoveries from the prime Kepler mission demonstrated that small planets (<3 ) 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 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,Rp/-Rfseq 1∗ = % and %, respectively. We obtained follow up NIR spectroscopy of K2-21 to constrain host star properties, which imply planet sizes of 1.59 ± 0.43 and 1.92 ± 0.53 , 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 a period ratio Pc/Pb = 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 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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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: File reproduced in accordance with the copyright policy of the publisher/author.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 31 May 2017 22:30
Last Modified: 13 Jul 2021 04:19
Uncontrolled Keywords: planets and satellites: detection; stars: individual (EPIC-206011691); techniques: photometric techniques: spectroscopic;
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
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