The Astronomical Journal (Jan 2023)
Hyades Member K2-136c: The Smallest Planet in an Open Cluster with a Precisely Measured Mass
- Andrew W. Mayo,
- Courtney D. Dressing,
- Andrew Vanderburg,
- Charles D. Fortenbach,
- Florian Lienhard,
- Luca Malavolta,
- Annelies Mortier,
- Alejandro Núñez,
- Tyler Richey-Yowell,
- Emma V. Turtelboom,
- Aldo S. Bonomo,
- David W. Latham,
- Mercedes López-Morales,
- Evgenya Shkolnik,
- Alessandro Sozzetti,
- Marcel A. Agüeros,
- Luca Borsato,
- David Charbonneau,
- Rosario Cosentino,
- Stephanie T. Douglas,
- Xavier Dumusque,
- Adriano Ghedina,
- Rose Gibson,
- Valentina Granata,
- Avet Harutyunyan,
- R. D. Haywood,
- Gaia Lacedelli,
- Vania Lorenzi,
- Antonio Magazzù,
- A. F. Martinez Fiorenzano,
- Giuseppina Micela,
- Emilio Molinari,
- Marco Montalto,
- Domenico Nardiello,
- Valerio Nascimbeni,
- Isabella Pagano,
- Giampaolo Piotto,
- Lorenzo Pino,
- Ennio Poretti,
- Gaetano Scandariato,
- Stephane Udry,
- Lars A. Buchhave
Affiliations
- Andrew W. Mayo
- ORCiD
- Astronomy Department, University of California , Berkeley, CA 94720, USA ; [email protected]; Centre for Star and Planet Formation, Natural History Museum of Denmark & Niels Bohr Institute, University of Copenhagen , Øster Voldgade 5-7, DK-1350 Copenhagen K., Denmark
- Courtney D. Dressing
- ORCiD
- Astronomy Department, University of California , Berkeley, CA 94720, USA ; [email protected]
- Andrew Vanderburg
- ORCiD
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- Charles D. Fortenbach
- ORCiD
- Department of Physics and Astronomy, San Francisco State University , San Francisco, CA 94132, USA
- Florian Lienhard
- ORCiD
- Astrophysics Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, UK
- Luca Malavolta
- ORCiD
- Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy
- Annelies Mortier
- ORCiD
- Astrophysics Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, UK; School of Physics & Astronomy, University of Birmingham , Edgbaston, Birmingham, B15 2TT, UK; Kavli Institute for Cosmology, University of Cambridge , Madingley Road, Cambridge CB3 0HA, UK
- Alejandro Núñez
- ORCiD
- Department of Astronomy, Columbia University , 550 West 120th Street, New York, NY 10027, USA
- Tyler Richey-Yowell
- ORCiD
- School of Earth and Space Exploration, Arizona State University , Tempe, AZ 85287, USA
- Emma V. Turtelboom
- ORCiD
- Astronomy Department, University of California , Berkeley, CA 94720, USA ; [email protected]
- Aldo S. Bonomo
- ORCiD
- INAF—Osservatorio Astrofisico di Torino, Via Osservatorio 20, I-10025 Pino Torinese, Italy
- David W. Latham
- ORCiD
- Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
- Mercedes López-Morales
- ORCiD
- Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
- Evgenya Shkolnik
- ORCiD
- School of Earth and Space Exploration, Arizona State University , Tempe, AZ 85287, USA
- Alessandro Sozzetti
- ORCiD
- INAF—Osservatorio Astrofisico di Torino, Via Osservatorio 20, I-10025 Pino Torinese, Italy
- Marcel A. Agüeros
- ORCiD
- Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux , CNRS, B18N, Allée Geoffroy Saint-Hilaire, F-33615 Pessac, France; Department of Astronomy, Columbia University , 550 West 120th Street, New York, NY 10027, USA
- Luca Borsato
- ORCiD
- INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
- David Charbonneau
- ORCiD
- Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
- Rosario Cosentino
- ORCiD
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain
- Stephanie T. Douglas
- ORCiD
- Department of Physics, Lafayette College, 730 High Street, Easton, PA 18042, USA
- Xavier Dumusque
- ORCiD
- Department of Astronomy of the University of Geneva, Geneva Observatory, Chemin Pegasi 51, 1290 Versoix, Switzerland
- Adriano Ghedina
- ORCiD
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain
- Rose Gibson
- Columbia University , Department of Astronomy, 550 West 120th Street, New York, NY 10027, USA
- Valentina Granata
- ORCiD
- Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy; INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
- Avet Harutyunyan
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain
- R. D. Haywood
- ORCiD
- Astrophysics Group, University of Exeter , Exeter EX4 2QL, UK
- Gaia Lacedelli
- ORCiD
- Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy; INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
- Vania Lorenzi
- ORCiD
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain; Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205 La Laguna, Spain
- Antonio Magazzù
- ORCiD
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain
- A. F. Martinez Fiorenzano
- ORCiD
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain
- Giuseppina Micela
- ORCiD
- INAF—Osservatorio Astronomico di Palermo , Piazza del Parlamento 1, I-90134 Palermo, Italy
- Emilio Molinari
- ORCiD
- INAF—Osservatorio Astronomico di Cagliari & REM , Via della Scienza, 5, I-09047 Selargius CA, Italy
- Marco Montalto
- ORCiD
- Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy; INAF—Osservatorio Astrofisico di Catania , Via Santa Sofia 78, I-95123 Catania, Italy
- Domenico Nardiello
- ORCiD
- INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy; Aix Marseille Univ , CNRS, CNES, LAM, Marseille, France
- Valerio Nascimbeni
- ORCiD
- INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
- Isabella Pagano
- ORCiD
- INAF—Osservatorio Astrofisico di Catania , Via Santa Sofia 78, I-95123 Catania, Italy
- Giampaolo Piotto
- ORCiD
- Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy; INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
- Lorenzo Pino
- ORCiD
- INAF—Osservatorio Astrofisico di Arcetri , Largo Enrico Fermi 5, I-50125, Firenze, Italy
- Ennio Poretti
- ORCiD
- Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Tenerife, Spain; INAF—Osservatorio Astronomico di Brera , Via E. Bianchi 46, I-23807 Merate, Italy
- Gaetano Scandariato
- ORCiD
- Aix Marseille Univ , CNRS, CNES, LAM, Marseille, France
- Stephane Udry
- ORCiD
- Department of Physics, Lafayette College, 730 High Street, Easton, PA 18042, USA
- Lars A. Buchhave
- ORCiD
- Centre for Star and Planet Formation, Natural History Museum of Denmark & Niels Bohr Institute, University of Copenhagen , Øster Voldgade 5-7, DK-1350 Copenhagen K., Denmark; DTU Space, National Space Institute, Technical University of Denmark , Elektrovej 327, DK-2800 Lyngby, Denmark
- DOI
- https://doi.org/10.3847/1538-3881/acca1c
- Journal volume & issue
-
Vol. 165,
no. 6
p. 235
Abstract
K2-136 is a late-K dwarf (0.742 ± 0.039 M _⊙ ) in the Hyades open cluster with three known, transiting planets and an age of 650 ± 70 Myr. Analyzing K2 photometry, we found that planets K2-136b, c, and d have periods of 8.0, 17.3, and 25.6 days and radii of 1.014 ± 0.050 R _⊕ , 3.00 ± 0.13 R _⊕ , and 1.565 ± 0.077 R _⊕ , respectively. We collected 93 radial velocity (RV) measurements with the High-Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph (Telescopio Nazionale Galileo) and 22 RVs with the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) spectrograph (Very Large Telescope). Analyzing HARPS-N and ESPRESSO data jointly, we found that K2-136c induced a semi-amplitude of 5.49 ± 0.53 m s ^−1 , corresponding to a mass of 18.1 ± 1.9 M _⊕ . We also placed 95% upper mass limits on K2-136b and d of 4.3 and 3.0 M _⊕ , respectively. Further, we analyzed Hubble Space Telescope and XMM-Newton observations to establish the planetary high-energy environment and investigate possible atmospheric loss. K2-136c is now the smallest planet to have a measured mass in an open cluster and one of the youngest planets ever with a mass measurement. K2-136c has ∼75% the radius of Neptune but is similar in mass, yielding a density of ${3.69}_{-0.56}^{+0.67}$ g cm ^−3 (∼2–3 times denser than Neptune). Mass estimates for K2-136b (and possibly d) may be feasible with more RV observations, and insights into all three planets’ atmospheres through transmission spectroscopy would be challenging but potentially fruitful. This research and future mass measurements of young planets are critical for investigating the compositions and characteristics of small exoplanets at very early stages of their lives and providing insights into how exoplanets evolve with time.
Keywords
- Exoplanets
- Exoplanet systems
- Exoplanet atmospheres
- Exoplanet detection methods
- Radial velocity
- Transits
