TOI-4504’s giant planets locked in deep resonance, echoing Gliese 876’s dynamics

Star system: Gliese 876 | Distance from the Sun: 15.2 light years

TOI-4504 is an orange dwarf star that hosts two giant planets, both orbiting in a special pattern called a 2:1 mean-motion resonance. This means that for every orbit the outer planet completes, the inner planet completes exactly two. The planets, named TOI-4504 c and d, have orbital periods of 82.8 and 41.3 days, respectively, and show some of the largest known variations in the timing of their transits across the star.

Recent data from the TESS mission revealed that the inner planet, previously not seen to transit, now does so due to a change in its orbital orientation. This allowed astronomers to update the system’s parameters, finding that both planets are deeply locked in resonance and exhibit complex gravitational interactions. These interactions cause their orbits to change in a predictable but intricate way, with their eccentricities and orbital alignments precessing together. The study also compares TOI-4504’s planetary system to that of GJ 876, showing that despite differences in their host stars, both systems share remarkably similar dynamical behaviors.

Key findings
- TOI-4504 hosts two giant planets in a 2:1 mean-motion resonance
- Both planets show large transit-timing variations, up to 5 and 3 days
- New TESS data revealed the inner planet now transits, enabling updated system parameters
- The planets’ orbits are deeply resonant and exhibit complex, coupled precession of eccentricities and alignments
- The system’s dynamics closely resemble those of the GJ 876 system, despite different host star types

Scientific study

Photodynamical modeling of TOI-4504 reveals its deeply resonant state and similarity to GJ 876 (external link)