The Origin of Universality in the Inner Edges of Planetary Systems

Abstract

The characteristic orbital period of the inner-most objects within the galactic census of planetary and satellite systems appears to be nearly universal, with $P$ on the order of a few days. This paper presents a theoretical framework that provides a simple explanation for this phenomenon. By considering the interplay between disk accretion, magnetic field generation by convective dynamos, and Kelvin-Helmholtz contraction, we derive an expression for the magnetospheric truncation radius in astrophysical disks, and find that the corresponding orbital frequency is independent of the mass of the host body. Our analysis demonstrates that this characteristic frequency corresponds to a period of $P\sim 3$ days, although intrinsic variations in system parameters are expected to introduce a factor of $\sim 2-3$ spread in this result. Standard theory of orbital migration further suggests that planets should stabilize at an orbital period that exceeds disk truncation by a small margin. Cumulatively, our findings predict that the periods of close-in bodies should span $P\sim 2-12$ days - a range that is consistent with observations.

9 pages, 4 figures, accepted to ApJL

References in corpus (11)

• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• UV excess measures of accretion onto young very low-mass stars and brown dwarfs
• Resonance locking in giant planets indicated by the rapid orbital expansion of Titan
• Magnetocentrifugally Driven Flows from Young Stars and Disks. VI. Accretion with a Multipole Stellar Field
• Architectures of Compact Super-Earth Systems Shaped by Instabilities
• Detecting exomoons from radial velocity measurements of self-luminous planets: application to observations of HR 7672 B and future prospects
• Pushing planets into an inner cavity by a resonant chain
• Uranian Satellite Formation by Evolution of a Water Vapor Disk Generated by a Giant Impact
• Hot Start Giant Planets Form With Radiative Interiors
• A Tidal Origin for a 3-body Resonance in Kepler-221
• The TEMPO Survey I: Predicting Yields of the Transiting Exosatellites, Moons, and Planets from a 30-day Survey of Orion with the Nancy Grace Roman Space Telescope

Cited by in corpus (4)

• On the suppression of giant planet formation around low-mass stars in clustered environments
• Small and Close-In Planets are Uncommon Around A-type Stars
• Planetary Edge Trends (PET). I. The Inner Edge-Stellar Mass Correlation
• Higher-Order Mean-Motion Resonances Can Form in Type-I Disk Migration