Kepler-102: Masses and Compositions for a Super-Earth and Sub-Neptune Orbiting an Active Star

Abstract

Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the Solar System. Kepler-102, which consists of 5 tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using radial velocities. Previous work found a high density for Kepler-102d, suggesting a composition similar to that of Mercury, while Kepler-102e was found to have a density typical of sub-Neptune size planets; however, Kepler-102 is an active star, which can interfere with RV mass measurements. To better measure the mass of these two planets, we obtained 111 new RVs using Keck/HIRES and TNG/HARPS-N and modeled Kepler-102's activity using quasi-periodic Gaussian Process Regression. For Kepler-102d, we report a mass upper limit of M${}_d<$5.3 M${}_{\oplus }$ [95\% confidence], a best-fit mass of M${}_d$=2.5 $\pm$ 1.4 M${}_{\oplus }$, and a density of ${\rho }_d$=5.6 $\pm$ 3.2 g/cm${}^3$ which is consistent with a rocky composition similar in density to the Earth. For Kepler-102e we report a mass of M${}_e$=4.7 $\pm$ 1.7 M${}_{\oplus }$ and a density of ${\rho }_e$=1.8 $\pm$ 0.7 g/cm${}^3$. These measurements suggest that Kepler-102e has a rocky core with a thick gaseous envelope comprising 2-4% of the planet mass and 16-50% of its radius. Our study is yet another demonstration that accounting for stellar activity in stars with clear rotation signals can yield more accurate planet masses, enabling a more realistic interpretation of planet interiors.

Accepted to AJ 11/08/2022

References in corpus (17)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Most 1.6 Earth-Radius Planets are not Rocky
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Growth Model Interpretation of Planet Size Distribution
• Extreme Water Loss and Abiotic O${}_2$ Buildup On Planets Throughout the Habitable Zones of M Dwarfs
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• Radius and Structure models for the First Super-Earth Planet
• The Mass of Kepler-93b and The Composition of Terrestrial Planets
• The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data
• The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
• A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system
• Coreless Terrestrial Exoplanets
• Thermal Emission from Transiting Very-Hot Jupiters: Prospects for Ground-based Detection at Optical Wavelengths
• Improved parameters of seven Kepler giant companions characterized with SOPHIE and HARPS-N
• K2-291 b: A rocky super-Earth in a 2.2 day orbit

Cited by in corpus (3)

• Cold Jupiters and improved masses in 38 Kepler and K2 small planet systems from 3661 HARPS-N radial velocities. No excess of cold Jupiters in small planet systems
• The Kepler Giant Planet Search. I: A Decade of Kepler Planet-host Radial Velocities from W. M. Keck Observatory
• Three young planets around the K-dwarf K2-198: High-energy environment, evaporation history and expected future