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ABSTRACT Consistent with the notion that most Sun-like stars form in multistellar systems, this study explores the impact of a temporarily bound stellar binary companion on the early dynamical evolution of the Solar system. Using N-body simulations, we illustrate how such a companion markedly enhances the trapping of scattered bodies on inner Oort cloud-like orbits, with perihelion distances exceeding $$q \gt 40$$ au. We further find that the orbital geometry of the Sun-binary system plays a central role in regulating the efficiency of small-body implantation on to high-perihelion orbits, and demonstrate that this process is driven by the von Zeipel–Kozai–Lidov mechanism. Incorporating the transiency of stellar clusters and the eventual Sun-binary pair dissociation due to passing stars, we show how the binary can be stripped away by an approximately solar-mass ejector star, with only a modest impact on the generated inner Oort cloud population. Collectively, our results highlight a previously underappreciated process that could have contributed to the formation of the inner Oort cloud. 

Abstract Orbital evolution is a critical process that sculpts planetary systems, particularly during their early stages where planet–disk interactions are expected to lead to the formation of resonant chains. Despite the theoretically expected prominence of such configurations, they are scarcely observed among long-period giant exoplanets. This disparity suggests an evolutionary sequence wherein giant planet systems originate in compact multiresonant configurations, but subsequently become unstable, eventually relaxing to wider orbits—a phenomenon mirrored in our own solar system’s early history. In this work, we present a suite ofN-body simulations that model the instability-driven evolution of giant planet systems, originating from resonant initial conditions, through phases of disk dispersal and beyond. By comparing the period ratio and normalized angular momentum distributions of our synthetic aggregate of systems with the observational census of long-period Jovian planets, we derive constraints on the expected rate of orbital migration, the efficiency of gas-driven eccentricity damping, and typical initial multiplicity. Our findings reveal a distinct inclination toward densely packed initial conditions, weak damping, and high giant planet multiplicities. Furthermore, our models indicate that resonant chain origins do not facilitate the formation of Hot Jupiters via the coplanar high-eccentricity pathway at rates high enough to explain their observed prevalence. 

Abstract The characteristic orbital period of the innermost objects within the galactic census of planetary and satellite systems appears to be nearly universal, withPon 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 ofP∼ 3 days although intrinsic variations in system parameters are expected to introduce a factor of a ∼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 spanP∼ 2–12 days—a range that is consistent with observations. 

Abstract Short-period super-Earths and mini-Neptunes encircle more than ∼50% of Sun-like stars and are relatively amenable to direct observational characterization. Despite this, environments in which these planets accrete are difficult to probe directly. Nevertheless, pairs of planets that are close to orbital resonances provide a unique window into the inner regions of protoplanetary disks, as they preserve the conditions of their formation, as well as the early evolution of their orbital architectures. In this work, we present a novel approach toward quantifying transit timing variations within multiplanetary systems and examine the near-resonant dynamics of over 100 planet pairs detected by Kepler. Using an integrable model for first-order resonances, we find a clear transition from libration to circulation of the resonant angle at a period ratio of ≈0.6% wide of exact resonance. The orbital properties of these systems indicate that they systematically lie far away from the resonant forced equilibrium. Cumulatively, our modeling indicates that while orbital architectures shaped by strong disk damping or tidal dissipation are inconsistent with observations, a scenario where stochastic stirring by turbulent eddies augments the dissipative effects of protoplanetary disks reproduces several features of the data. 

ABSTRACT The trans-Neptunian scattered disc exhibits unexpected dynamical structure, ranging from an extended dispersion of perihelion distance to a clustered distribution in orbital angles. Self-gravitational modulation of the scattered disc has been suggested in the literature as an alternative mechanism to Planet nine for sculpting the orbital architecture of the trans-Neptunian region. The numerics of this hypothesis have hitherto been limited to N < O(103) superparticle simulations that omit direct gravitational perturbations from the giant planets and instead model them as an orbit-averaged (quadrupolar) potential, through an enhanced J2 moment of the central body. For sufficiently massive discs, such simulations reveal the onset of collective dynamical behaviour – termed the ‘inclination instability’ – wherein orbital circularisation occurs at the expense of coherent excitation of the inclination. Here, we report N = O(104) GPU-accelerated simulations of a self-gravitating scattered disc (across a range of disc masses spanning 5–40 M⊕) that self-consistently account for intraparticle interactions as well as Neptune’s perturbations. Our numerical experiments show that even under the most favourable conditions, the inclination instability never ensues. Instead, due to scattering, the disc depletes. While our calculations show that a transient lopsided structure can emerge within the first few hundreds of Myr, the terminal outcomes of these calculations systematically reveal a scattered disc that is free of any orbital clustering. We conclude thus that the inclination instability mechanism is an inadequate explanation of the observed architecture of the Solar system. 

The dynamics of the outer regular satellites of Saturn are driven primarily by the outward migration of Titan, but several independent constraints on Titan's migration are difficult to reconcile with the current resonant orbit of the small satellite Hyperion. We argue that Hyperion's rapid irregular tumbling greatly increases tidal dissipation with a steep dependence on orbital eccentricity. Resonant excitation from a migrating Titan is then balanced by damping in a feedback mechanism that maintains Hyperion's eccentricity without fine-tuning. The inferred tidal parameters of Hyperion are most consistent with rapid Titan migration enabled by a resonance lock with an internal mode of Saturn, but a scenario with only equilibrium dissipation in Saturn is also possible. 

The emergence of orbital resonances among planets is a natural consequence of the early dynamical evolution of planetary systems. While it is well established that convergent migration is necessary for mean-motion commensurabilities to emerge, recent numerical experiments have shown that the existing adiabatic theory of resonant capture provides an incomplete description of the relevant physics, leading to an erroneous mass scaling in the regime of strong dissipation. In this work, we develop a new model for resonance capture that self-consistently accounts for migration and circularization of planetary orbits, and derive an analytic criterion based upon stability analysis that describes the conditions necessary for the formation of mean-motion resonances. We subsequently test our results against numerical simulations and find satisfactory agreement. Our results elucidate the critical role played by adiabaticity and resonant stability in shaping the orbital architectures of planetary systems during the nebular epoch, and provide a valuable tool for understanding their primordial dynamical evolution. 

The formation of super-Earths, the most abundant planets in the Galaxy, remains elusive. These planets have masses that typically exceed that of the Earth by a factor of a few, appear to be predominantly rocky, although often surrounded by H/He atmospheres, and frequently occur in multiples. Moreover, planets that encircle the same star tend to have similar masses and radii, whereas those belonging to different systems exhibit remarkable overall diversity. Here we advance a theoretical picture for rocky planet formation that satisfies the aforementioned constraints: building upon recent work, which has demonstrated that planetesimals can form rapidly at discrete locations in the disk, we propose that super-Earths originate inside rings of silicate-rich planetesimals at approximately ~1 au. Within the context of this picture, we show that planets grow primarily through pairwise collisions among rocky planetesimals until they achieve terminal masses that are regulated by isolation and orbital migration. We quantify our model with numerical simulations and demonstrate that our synthetic planetary systems bear a close resemblance to compact, multi-resonant progenitors of the observed population of short-period extrasolar planets. 

Uncovering the formation process that reproduces the distinct properties of compact super-Earth exoplanet systems is a major goal of planet formation theory. The most successful model argues that non-resonant systems begin as resonant chains of planets that later experience a dynamical instability. However, both the boundary of stability in resonant chains and the mechanism of the instability itself are poorly understood. Previous work postulated that a secondary resonance between the fastest libration frequency and a difference in synodic frequencies destabilizes the system. Here, we use that hypothesis to produce a simple and general criterion for resonant chain stability that depends only on planet orbital periods and masses. We show that the criterion accurately predicts the maximum mass of planets in synthetic resonant chains up to six planets. More complicated resonant chains produced in population synthesis simulations are found to be less stable than expected, although our criterion remains useful and superior to machine learning models. 

Various physical processes that ensue within protoplanetary disks - including vertical settling of icy and rocky grains, radial drift of solids, planetesimal formation, as well as planetary accretion itself - are facilitated by hydrodynamic interactions between H/He gas and high-Z dust. The Stokes number, which quantifies the strength of dust-gas coupling, thus plays a central role in protoplanetary disk evolution and its poor determination constitutes an important source of uncertainty within the theory of planet formation. In this work, we present a simple model for dust-gas coupling and we demonstrate that for a specified combination of the nebular accretion rate,Ṁ, and turbulence parameter a, the radial profile of the Stokes number can be calculated in a unique way. Our model indicates that the Stokes number grows sublinearly with the orbital radius, but increases dramatically across the water-ice line. For fiducial protoplanetary disk parameters ofṀ= 10⁻⁸M_⊙per year andα= 10⁻³, our theory yields characteristic values of the Stokes number on the order of St ~ 10⁻⁴(corresponding to ~mm-sized silicate dust) in the inner nebula and St ~ 10⁻¹(corresponding to icy grains of a few cm in size) in the outer regions of the disk. Accordingly, solids are expected to settle into a thin subdisk at large stellocentric distances, while remaining vertically well mixed inside the ice line.