Kepler-102: masses and compositions for a super-Earth and sub-Neptune orbiting an active star

Casey L. Brinkman*, James Cadman, Lauren Weiss, Eric Gaidos, Ken Rice, Daniel Huber, Zachary R. Claytor, Aldo S. Bonomo, Lars A. Buchhave, Andrew Collier Cameron, Rosario Cosentino, Xavier Dumusque, Aldo F. Martinez Fiorenzano, Adriano Ghedina, Avet Harutyunyan, Andrew Howard, Howard Isaacson, David W. Latham, Mercedes López-Morales, Luca MalavoltaGiuseppina Micela, Emilio Molinari, Francesco Pepe, David F. Philips, Ennio Poretti, Alessandro Sozzetti, Stéphane Udry

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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 five 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 RVs. 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 Telescopio Nazionale Galileo/HARPS-N and modeled Kepler-102's activity using quasiperiodic Gaussian process regression. For Kepler-102d, we report a mass upper limit Md < 5.3 M (95% confidence), a best-fit mass Md = 2.5 ± 1.4 M, and a density ρd = 5.6 ± 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 Me = 4.7 ± 1.7 M and a density ρe = 1.8 ± 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.
Original languageEnglish
Article number74
Number of pages14
JournalAstronomical Journal
Issue number2
Early online date27 Jan 2023
Publication statusPublished - 1 Feb 2023


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