2025ApJ...988L..18B

Most observed multiplanet systems are coplanar, in a dynamically “cold” configuration of concentric orbits like our own solar system. With the James Webb Space Telescope, we have detected 14 Her c, the first mature and cold exoplanet directly imaged in a dynamically “hot” multiplanet system. With large eccentricities and a nonzero mutual inclination, the present-day architecture of this system points to a turbulent past and ongoing angular momentum exchange between the planetary orbits of 14 Her b and c. The temperature of 14 Her c rivals both the coldest imaged exoplanet and the coldest known brown dwarf. Moreover, its photometry at 4.4 μm is consistent with the presence of carbon disequilibrium chemistry and water-ice clouds in its atmosphere. 14 Her c presents a unique laboratory to study giant planet formation, the dynamical evolution of multiplanet system architectures, and atmospheric composition and dynamics in extremely cold worlds.