The Dynamical Environment within the Habitable Zone of the Gaia-4 and Gaia-5 Planetary Systems

Exoplanetary systems exhibit a broad range of architectures, which, in turn, enables a variety of dynamical environments. Many of the known planetary systems do not transit the host star, and so we measure the minimum masses of their planets, making it difficult to fully assess the dynamical environment within the system. Astrometry can resolve the mass ambiguity and thus allow a more complete dynamical analysis of systems to be conducted. Gaia-4 and Gaia-5 are two such systems, whose study with radial velocities and data from the Gaia mission revealed that each star harbors a massive planet on a highly eccentric orbit. In this work, we provide the results of a dynamical analysis of each system, including calculations of the Habitable Zone (HZ), from which we show that the presence of the known companions largely excludes the presence of planets within the HZ. We discuss the diagnostics of potential past planet–planet scattering events, and the occurrence of similar systems whereby a giant planet on an eccentric orbit can substantially disrupt the orbital integrity of terrestrial planets. These “wrecking ball” systems have an impact on the target selection for planned direct imaging missions that seek to identify potentially habitable environments.