2018MNRAS.478.2480P

We study the orbital architecture, physical characteristics of planets, formation and long-term evolution of the Kepler-30 planetary system, detected and announced in 2012 by the Kepler team. We show that the Kepler-30 system belongs to a particular class of very compact and quasi-resonant, yet long-term stable planetary systems. We re-analyse the light curves of the host star spanning Q1-Q17 quarters of the Kepler mission. A huge variability of the Transit Timing Variations exceeding 2 d is induced by a massive Jovian planet located between two Neptune-like companions. The innermost pair is near to the 2:1 mean motion resonance (MMR), and the outermost pair is close to higher order MMRs, such as 17:7 and 7:3. Our re-analysis of photometric data allows us to constrain, better than before, the orbital elements, planets' radii, and masses, which are 9.2 ± 0.1, 536 ± 5, and 23.7 ± 1.3 Earth masses for Kepler-30b, Kepler-30c, and Kepler-30d, respectively. The masses of the inner planets are determined within ∼1 per cent uncertainty. We infer the internal structures of the Kepler-30 planets and their bulk densities in a wide range from 0.19 ± 0.01 g*cm^–3 for Kepler-30d, 0.96 ± 0.15 g*cm^–3 for Kepler-30b, to 1.71 ± 0.13 g*cm^–3 for the Jovian planet Kepler-30c. We attempt to explain the origin of this unique planetary system and a deviation of the orbits from exact MMRs through the planetary migration scenario. We anticipate that the Jupiter-like planet plays an important role in determining the present dynamical state of this system.