New Dynamical State and Habitability of the HD 45364 Planetary System

TL;DR

This study revises the orbital parameters and dynamical state of the HD 45364 system using extended observational data, revealing a quasi-resonance state and potential habitability prospects for additional planets and moons.

Contribution

The paper provides updated orbital solutions and dynamical analysis of HD 45364, supporting near circular orbits and exploring habitability with possible Earth-mass planets and exomoons.

Findings

Revised orbits are more circular and separated.

System exhibits quasi-resonance, not true MMR.

Potential for habitable Earth-mass planets and exomoons.

Abstract

Planetary systems with multiple giant planets provide important opportunities to study planetary formation and evolution. The HD 45364 system hosts two giant planets that reside within the Habitable Zone (HZ) of their host star and was the first system discovered with a 3:2 mean motion resonance (MMR). Several competing migration theories with different predictions have previously provided explanations regarding the observed resonance through dynamical simulations that utilized limited data. Here, over ten years since the original discovery, we revisit the system with a substantially increased radial velocity (RV) sample from HARPS and HIRES that significantly extend the observational baseline. We present the revised orbital solutions for the two planets using both Keplerian and dynamical models. Our RV models suggest orbits that are more circular and separated than those previously reported. As a result, predicted strong planet-planet interactions were not detected. The system dynamics were reanalyzed, and the planet pair was found to exhibit apsidal behavior of both libration and circulation, indicating a quasi-resonance state rather than being truly in MMR. The new orbital solution and dynamical state of the system confirm migration models that predicted near circular orbits as the preferred scenario. We also study the habitability prospects of this system and found that an additional Earth-mass planet and exomoons in the HZ are possible. This work showcases the importance of continued RV observation and its impact on our knowledge of the system's dynamical history. HD 45364 continues to be an interesting target for both planetary formation and habitability studies.