A Six-planet Resonance Chain in K2-138?

Abstract The K2-138 system hosts six planets and presents an interesting case study due to its distinctive dynamical structure. Its five inner are near a chain of 3/2 two-body mean-motion resonances, while the outermost body (planet g) is significantly detached, having ratio n f / g ∼ 3.3 with closest neighbor. We show that orbit m actually consistent first-order three-planet resonance (3P-MMR) characterized by relation 2 e − 4 + 3 = 0 first time pure 3P-MMR has been found in multiplanet tied current Adequate values for masses allow one trace history from initial capture six-planet (with 3/1 resonance) up configuration tidal interactions over age star. increase offset semimajor axis, as well large value , can be explained slopes resonances plane. triplets slide outward these curves when innermost pair pulled apart effects, pantograph- like manner. into surprisingly robust given similar it possible same effect may also other compact planetary systems.