The CARMENES search for exoplanets around M dwarfs. Dynamical characterization of the multiple planet system GJ 1148 and prospects of habitable exomoons around GJ 1148 b
Schmitt, J. H. M. M.; Amado, P. J.; Bauer, F. F.; Caballero, J. A.; Reiners, A.; Ribas, I.; Quirrenbach, A.; Béjar, V. J. S.; Kaminski, A.; Kürster, M.; Montes, D.; Morales, J. C.; Zechmeister, M.; Cortés-Contreras, M.; Azzaro, M.; Dreizler, S.; Jeffers, S. V.; Lafarga, M.; Hatzes, A. P.; Henning, Th.; Solano, E.; Rodríguez-López, C.; Stock, S.; Reffert, S.; Kossakowski, D.; Pavlov, A.; Trifonov, T.; Barnes, R.; Lee, M. H.; Grishin, E.; Tjoa, J.; Wong, K. H.
Germany, Hong Kong SAR, Israel, Netherlands, Spain, United States
Abstract
Context. GJ 1148 is an M-dwarf star hosting a planetary system composed of two Saturn-mass planets in eccentric orbits with periods of 41.38 and 532.02 days.
Aims: We reanalyze the orbital configuration and dynamics of the GJ 1148 multi-planetary system based on new precise radial velocity measurements taken with CARMENES.
Methods: We combined new and archival precise Doppler measurements from CARMENES with those available from HIRES for GJ 1148 and modeled these data with a self-consistent dynamical model. We studied the orbital dynamics of the system using the secular theory and direct N-body integrations. The prospects of potentially habitable moons around GJ 1148 b were examined.
Results: The refined dynamical analyses show that the GJ 1148 system is long-term stable in a large phase-space of orbital parameters with an orbital configuration suggesting apsidal alignment, but not in any particular high-order mean-motion resonant commensurability. GJ 1148 b orbits inside the optimistic habitable zone (HZ). We find only a narrow stability region around the planet where exomoons can exist. However, in this stable region exomoons exhibit quick orbital decay due to tidal interaction with the planet.
Conclusions: The GJ 1148 planetary system is a very rare M-dwarf planetary system consisting of a pair of gas giants, the inner of which resides in the HZ. We conclude that habitable exomoons around GJ 1148 b are very unlikely to exist.