A Tale of Two Peas in a Pod: The Kepler-323 and Kepler-104 Systems

A Tale of Two Peas in a Pod: The Kepler-323 and Kepler-104 Systems

In order to understand the relationship between planet multiplicity, mass, and composition, we present newly measured masses of five planets in two planetary systems: Kepler-323 and Kepler-104. We used the HIRES instrument at the W.M. Keck Observatory to collect 79 new radial velocity (RV) measurements for Kepler-323, which we combined with 48 literature RVs from TNG/HARPS-N. We also conducted a reanalysis of the Kepler104 system, using 44 previously published RV measurements. Kepler-323 b and c have masses of - + 2.0 1.1 1.2 M⊕ and 6.5±1.6 M⊕, respectively, whereas the three Kepler-104 planets are more massive (10.0±2.8 M⊕, - + 7.1 3.5 3.8 M⊕, and - + 5.5 3.5 4.6 M⊕ for planets b, c, and d, respectively). The Kepler-104 planets have densities consistent with rocky cores overlaid with gaseous envelopes ( - + 4.1 1.1 1.2 g cc−1 , - + 2.9 1.5 1.7 g cc−1 , and - + 1.6 1.1 1.5 g cc−1 respectively), whereas the Kepler-323 planets are consistent with having rocky compositions ( - + 4.5 2.4 2.8 g cc−1 and - + 9.9 2.5 2.7 g cc−1 ). The Kepler104 system has among the lowest values for gap complexity ( = 0.004) and mass partitioning ( = 0.03); whereas, the Kepler-323 planets have a mass partitioning similar to that of the Inner Solar System ( = 0.28 and  = 0.24, respectively). For both exoplanet systems, the uncertainty in the mass partitioning is affected equally by (1) individual mass errors of the planets and (2) the possible existence of undetected low-mass planets, meaning that both improved mass characterization and improved sensitivity to low-mass planets in these systems would better elucidate the mass distribution among the planets