Architecture of the Ancient Five-Planet Host System Kepler-444

Stellar multiple systems are the ubiquitous products of star formation. Therefore, a substantial fraction of exoplanets likely form in dynamical environments sculpted by stellar multiplicity, with distinct formation histories and orbital architectures from those with single stellar hosts. The planetary system Kepler-444 provides an excellent laboratory for studying the impact of stellar multiplicity on planet formation. This system is composed of a host star (Kepler-444A) with five transiting sub-Earth planets and a tight spectroscopic binary (Kepler-444BC) orbiting the entire compact (~0.1au) planetary system. Despite the complex environment, Kepler-444 has survived since its formation ~11Gyr ago. We present new constraints on the Keper-444A-BC orbit by combining multi-epoch high-precision adaptive optics images (spanning 6 years) and radial velocities (spanning 12 years). Our data expand a much longer baseline compared to previous studies and we have also implemented the significant acceleration revealed by the Hipparcos and Gaia astrometry, thereby providing the latest and more accurate characterization of the system architecture. Our revised orbit sheds new insights into the properties of Kepler-444’s protoplanetary disk and its implications on the observed size, mass, and orbital period of the five exoplanets.