TY - JOUR

T1 - Hyades Member K2-136c

T2 - The Smallest Planet in an Open Cluster with a Precisely Measured Mass

AU - Mayo, Andrew W.

AU - Dressing, Courtney D.

AU - Vanderburg, Andrew

AU - Fortenbach, Charles D.

AU - Lienhard, Florian

AU - Malavolta, Luca

AU - Mortier, Annelies

AU - Núñez, Alejandro

AU - Richey-Yowell, Tyler

AU - Turtelboom, Emma V.

AU - Bonomo, Aldo S.

AU - Latham, David W.

AU - López-Morales, Mercedes

AU - Shkolnik, Evgenya

AU - Sozzetti, Alessandro

AU - Agüeros, Marcel A.

AU - Borsato, Luca

AU - Charbonneau, David

AU - Cosentino, Rosario

AU - Douglas, Stephanie T.

AU - Dumusque, Xavier

AU - Ghedina, Adriano

AU - Gibson, Rose

AU - Granata, Valentina

AU - Harutyunyan, Avet

AU - Haywood, R. D.

AU - Lacedelli, Gaia

AU - Lorenzi, Vania

AU - Magazzù, Antonio

AU - Martinez Fiorenzano, A. F.

AU - Micela, Giuseppina

AU - Molinari, Emilio

AU - Montalto, Marco

AU - Nardiello, Domenico

AU - Nascimbeni, Valerio

AU - Pagano, Isabella

AU - Piotto, Giampaolo

AU - Pino, Lorenzo

AU - Poretti, Ennio

AU - Scandariato, Gaetano

AU - Udry, Stephane

AU - Buchhave, Lars A.

N1 - Publisher Copyright: © 2023. The Author(s). Published by the American Astronomical Society.

PY - 2023/5/10

Y1 - 2023/5/10

N2 - 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.

AB - 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.

U2 - 10.3847/1538-3881/acca1c

DO - 10.3847/1538-3881/acca1c

M3 - Journal article

AN - SCOPUS:85159197978

VL - 165

JO - The Astronomical Journal

JF - The Astronomical Journal

SN - 0004-6256

IS - 6

M1 - 235

ER -