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.
PY - 2023/6/1
Y1 - 2023/6/1
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 - Article
SN - 0004-6256
VL - 165
JO - The Astronomical Journal
JF - The Astronomical Journal
IS - 6
M1 - 235
ER -