A substantial fraction of our solar system's trans-Neptunian objects (TNOs) are in mean-motion resonance with Neptune. Many of these objects were likely caught into resonances by planetary migration-either smooth or stochastic-approximately 4 Gyr ago. Some, however, gravitationally scattered off of Neptune and became transiently stuck in more recent events. Here we use numerical simulations to predict the number of transiently stuck objects, captured from the current actively scattering population, that occupy 111 resonances at semimajor axes a=30-100au. Our source population is an observationally constrained model of the currently scattering TNOs. We predict that, integrated across all resonances at these distances, the current transient-sticking population comprises 40% of the total transiently stuck+scattering TNOs, suggesting that these objects should be treated as a single population. We compute the relative distribution of transiently stuck objects across all p:q resonances with q p 1 6 1 < , p<40, and q<20, providing predictions for the population of transient objects with H r <8.66 in each resonance. We find that the relative populations are approximately proportional to each resonance's libration period and confirm that the importance of transient sticking increases with semimajor axis in the studied range. We calculate the expected distribution of libration amplitudes for stuck objects and demonstrate that observational constraints indicate that both the total number and the amplitude distribution of 5:2 resonant TNOs are inconsistent with a population dominated by transient sticking from the current scattering disk. The 5:2 resonance hence poses a challenge for leading theories of Kuiper Belt sculpting.
We discuss the detection in the Outer Solar System Origins Survey (OSSOS) of two objects in Neptune's distant 9:1 mean motion resonance at semimajor axis a ≈ 130 au. Both objects are securely resonant on 10 Myr timescales, with one securely in the 9:1 resonance's leading asymmetric libration island and the other in either the symmetric or trailing asymmetric island. These objects are the largest semimajor axis objects with secure resonant classifications, and their detection in a carefully characterized survey allows for the first robust resonance population estimate beyond 100 au. The detection of these objects implies a 9:1 resonance population of 1.1 × 10 4 objects with H r < 8.66 (D 100 km) on similar orbits (95% confidence range of ∼ 0.4 − 3 × 10 4 ). Integrations over 4 Gyr of an ensemble of clones spanning these objects' orbit fit uncertainties reveal that they both have median resonance occupation timescales of ∼ 1 Gyr. These timescales are consistent with the hypothesis that these objects originate in the scattering population but became transiently stuck to Neptune's 9:1 resonance within the last ∼ 1 Gyr of solar system evolution. Based on simulations of a model of the current scattering population, we estimate the expected resonance sticking population in the 9:1 resonance to be 1000-4500 objects with H r < 8.66; this is marginally consistent with the OSSOS 9:1 population estimate. We conclude that resonance sticking is a plausible explanation for the observed 9:1 population, but we also discuss the possibility of a primordial 9:1 population, which would have interesting implications for the Kuiper belt's dynamical history.
Aims. The origin of close-in Jovian planets is still elusive. We examine the in-situ gas accretion scenario as a formation mechanism of these planets. Methods. We reconstruct natal disk properties from the occurrence rate distribution of close-in giant planets, under the assumption that the occurrence rate may reflect the gas accretion efficiency onto cores of these planets.Results. We find that the resulting gas surface density profile becomes an increasing function of the distance from the central star with some structure at r 0.1 au. This profile is quite different from the standard minimum-mass solar nebula model, while our profile leads to better reproduction of the population of observed close-in super-Earths based on previous studies. We compute the resulting magnetic field profiles and find that our profiles can be fitted by stellar dipole fields (∝ r −3 ) in the vicinity of the central star and large-scale fields (∝ r −2 ) at the inner disk regions, either if the isothermal assumption breaks down or if nonideal MHD effects become important. For both cases, the transition between these two profiles occurs at r 0.1 au, which corresponds to the period valley of giant exoplanets. Conclusions. Our work provides an opportunity to test the in-situ gas accretion scenario against disk quantities, which may constrain the gas distribution of the minimum-mass extrasolar nebula.
We present a physically motivated model for the manner in which a stellar magnetic field sculpts the inner edge of a protoplanetary disk, and examine the consequence for the migration and stopping of sub-Neptune and super-Earth planets. This model incorporates a transition zone exterior to the inner truncation of the disk, where the surface density profile is modified by the diffusion of the stellar magnetic field into the disk. This modification results in a migration trap at the outer edge of the transition zone. We performed simulations of single planet migration, considering a range of stellar magnetic field strengths and magnetic diffusion profiles. Our simulations show a tight relationship between the final locations of planets and the total magnetic budget available for the disk from their host star. We found that a stellar magnetic field between 67 to 180G and a power-law index between 3 and 2.75 can reasonably reproduce the location at which the observed occurrence rate of close-in Super-Earth and Sub-Neptune populations changes slope.
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