Speaker
Description
In multiple-planet systems, gravitational interactions of exoplanets could lead to transit timing variations (TTVs), whose amplitude becomes significantly enhanced when planets are near mean-motion resonances (MMRs), making them more easily detectable. In cases where both TTVs and radial velocity (RV) measurements are available, combined analysis can break degeneracies and provide robust planetary, and system characterization. In this context, HIP 41378 hosts five transiting planets with periods ranging from 15 to over 540 days, providing a unique dynamical laboratory for investigating wide multi-planet systems analogous to our own. In this study, we present an intensive space-based photometric follow-up of HIP 41378, combining 15 new CHEOPS observations with eight TESS sectors, alongside data from K2, Spitzer, HST, and 311 HARPS spectra. Using the N-body integrator within TRADES, we dynamically modeled the TTVs and RV signals of the two inner sub-Neptunes. These planets, HIP 41378 b (Pb = 15.57 days, Rb = 2.45 R⊕) and HIP 41378 c (Pc = 31.71 days, Rc = 2.57 R⊕), are nearly (~1.8%) in a 2:1 period commensurability. We report a clear detection of anti-correlated TTVs with amplitudes of 20 minutes for planet b and greater than 3 hours for planet c. We dynamically confirm the planetary nature of HIP 41378 g, a non-transiting planet with a period of about 64 days and a mass of about 8 M⊕, close to a 2:1 commensurability with planet c, suggesting a possible mean-motion resonance chain in the system. Our precise determination of the masses, eccentricities, and radii of these planets enabled us to constrain their volatile-rich compositions and reconstruct the evolutionary histories of their primordial atmospheres. Additionally, we demonstrated how the two inner planets are excellent candidates for atmospheric characterization with the NIRSpec/Prism instrument aboard JWST. Finally, we provide new insights into the three outer planets (P > 300 days), constraining the period of HIP 41378 d and suggesting a number of aliases for HIP 41378 e. Our analysis suggests that the system could be placed in a double resonant chain, highlighting its complex dynamical architecture.
