Ages of “Singles” versus “Multis”: Predictions for Dynamical Sculpting over Gyr in the Kepler Sample

Abstract

The sample of host stars with multiple transiting planets has illuminated the orbital architectures of exoplanetary systems. These architectures may be shaped mostly by formation conditions, be continually sculpted by ongoing dynamical processes, or both. As more studies have placed planet occurrence within a galactic context, evidence has emerged for variable planet multiplicity over time. In this manuscript, we investigate the use of transit multiplicity as a tool to constrain longer-timescale (>1 Gyr) dynamical sculpting. First, with a suite of injection-and-recovery tests, we quantify sensitivity to sculpting laws across different regimes. We employ a forward modeling framework in which we generate synthetic planetary systems, according to a prescribed sculpting speed and timescale, around the FGK dwarfs studied by the Kepler Mission. Some sculpting scenarios are hypothetically detectable in the Kepler sample, while others can be disfavored from Kepler transit statistics alone. Second, we apply our analysis to reverse engineer the sculpting laws consistent with the true yield from Kepler. We confirm the present-day fraction of host stars containing dynamically cool “systems with tightly packed inner planets” is 4%–13%. A variety of Gyr-timescale sculpting laws successfully predict the transit multiplicity of the Kepler sample, but none of these laws succeed in also producing a detectable trend with transit multiplicity and stellar age. An improvement to measured stellar age precision may help uncover such a sculpting law, but nevertheless reflects limitations in transit multiplicity as an observable. Therefore, other phenomena, apart from Gyr-timescale dynamical sculpting, may be required to explain the Kepler yield.

Keywords

• Exoplanet dynamics
• Planetary system evolution