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Abstract Planet migration in protoplanetary disks significantly influences exoplanet architectures. We investigate various migration mechanisms for young planets close to young stars. To quantify the stochastic migration driven by turbulent disks, we incorporate planets into existing 3D MHD-disk simulations of magnetospheric accretion. We further model these turbulent torques analytically using a modified Gaussian process. Migration timescales for other processes, including the smooth Type I/II migration, planet–star tidal and magnetic interactions, and aerodynamical drag with the magnetosphere are also estimated analytically. Given that our simulation reveals a very low surface density for this very inner MHD-turbulent region, the resulting disk migration here is significantly slower than previously estimated. Earth-mass planets have migration timescalest_mig≳ 10⁸yr in this region. Thus, they are unlikely to migrate past the dead zone inner boundary (R_DZIB) into the MHD-region before the disk dissipates. Only giant planets could migrate inward within the turbulent disk, and may stall at the magnetospheric truncation radius (R_T). A simplified planet population synthesis demonstrates that, at the end of the disk phase, all planets around solar-mass stars typically stall at ≲0.1 au, sinceR_T∼R_DZIB. However, around 2M_⊙stars, higher-mass planets stall significantly closer to the star compared to low-mass planets, due toR_T≪R_DZIB. These results are consistent with recent exoplanet demographics around different types of stars. Finally, the turbulence in our simulations may not be sufficient to break resonant planet pairs according to previous analytical criteria, which, on the other hand, needs to be confirmed by future 3D simulations. 

Abstract Shadows are commonly observed in protoplanetary disks in near-infrared (NIR) and (sub)millimeter images, often cast by misaligned inner disks or other obscuring material. While recent studies show that shadows can alter disk dynamics, only the case symmetric across the midplane (e.g., from a polar-aligned inner disk) has been studied. Here we study shadows cast by an inner disk with a 30° mutual inclination using 3D radiation–hydrodynamical simulations. Given the same shadow shape and amplitude, the 30° inclined shadow leads to a much stronger accretion compared with the polar case, reachingα ∼ 1, because the disk is squeezed twice in one azimuth, leading to shocks and strong radial flows near the midplane. The outer disk develops a warp: the inner disk region tilts toward alignment with the shadow, while the outer, exponentially tapered disk tilts and twists in a different direction, inclined ∼ 32° relative to the inner region. Locally isothermal simulations with a prescribed temperature structure reproduce the effect, confirming that it is thermally driven. Fourier–Hermite analysis shows that it is them= 1,n= 1 temperature perturbation that drives the warp by launching bending waves, with the tilting response of the disk approximately proportional to the modal amplitude. This mode always exists unless the shadow is coplanar or polar. Given a fixed temperature contrast, them= 1,n= 1 mode peaks at an ∼15° mutual inclination, but still contributes substantially across 3°–30°. Shadows cause disk warps—they are not only a consequence of them. We discuss testable predictions for current and future Atacama Large Millimeter/submillimeter Array and NIR observations. 

Abstract Recent discoveries of streamer-like structures around protostellar sources challenge the traditional picture of isolated, axisymmetric star formation. Here, we present new Atacama Large Millimeter/submillimeter Array observations of [BHB2007]-1, a flat-spectrum source connected to at least three such elongated structures. Two of these features are symmetrically located to the north and south of the disk, with velocities aligned with the disk on their respective sides. However, their unbound kinematics and curved morphology make it difficult to determine their origin. Possible explanations include outflows, interactions with the nearby [BHB2007]-2 system, and hyperbolic infall, but none fully account for all observed properties. In contrast, a newly identified collimated structure to the west shows clear evidence of gravitationally bound infall. Estimates of its mass, mass infall rate, and angular momentum suggest that this infalling streamer would roughly double the mass budget available to form planets and tilt the disk by a few tens of degrees. Furthermore, its misalignment with the midplane of the disk and the lack of diffuse envelope emission indicate that the streamer may have formed due to gravitational capture of cloud material unrelated to the source’s natal core. Together, these findings support a more dynamic picture of star formation, one where environmental interactions continue to shape the conditions for building planetary systems. 

Abstract The initial stellar carbon-to-oxygen (C/O) ratio can have a large impact on the resulting condensed species present in the protoplanetary disk and, hence, the composition of the bodies and planets that form. The observed C/Os of stars can vary from 0.1–1. We use a sequential dust condensation model to examine the impact of the C/O on the composition of solids around a solar-like star. We utilize this model in a focused examination of the impact of varying the initial stellar C/O to isolate the effects of the C/O in the context of solar-like stars. We describe three different system types in our findings. The solar system falls into the silicate-dominant, low-C/O systems which end at a stellar C/O somewhere between 0.52 and 0.6. At C/Os between about 0.6 and 0.9, we have intermediate systems. Intermediate systems show a decrease in silicates while carbides begin to become significant. Carbide-dominant systems begin around a C/O of 0.9. Carbide-dominant systems exhibit high carbide surface densities at inner radii with comparable levels of carbides and silicates at outer radii. Our models show that changes between C/O = 0.8 and C/O = 1 are more significant than previous studies, that carbon can exceed 80% of the condensed mass, and that carbon condensation can be significant at radii up to 6 au. 

ABSTRACT Recent high angular resolution ALMA observations have revealed rich information about protoplanetary discs, including ubiquitous substructures and three-dimensional gas kinematics at different emission layers. One interpretation of these observations is embedded planets. Previous 3D planet–disc interaction studies are either based on viscous simulations or non-ideal magnetohydrodynamics (MHD) simulations with simple prescribed magnetic diffusivities. This study investigates the dynamics of gap formation in 3D non-ideal MHD discs using non-ideal MHD coefficients from the look-up table that is self-consistently calculated based on the thermochemical code. We find a concentration of the poloidal magnetic flux in the planet-opened gap (in agreement with previous work) and enhanced field-matter coupling due to gas depletion, which together enable efficient magnetic braking of the gap material, driving a fast accretion layer significantly displaced from the disc mid-plane. The fast accretion helps deplete the gap further and is expected to negatively impact the planet growth. It also affects the corotation torque by shrinking the region of horseshoe orbits on the trailing side of the planet. Together with the magnetically driven disc wind, the fast accretion layer generates a large, persistent meridional vortex in the gap, which breaks the mirror symmetry of gas kinematics between the top and bottom disc surfaces. Finally, by studying the kinematics at the emission surfaces, we discuss the implications of planets in realistic non-ideal MHD discs on kinematics observations. 

Data associated with Huang et al., "High Resolution ALMA Observations of Richly Structured Protoplanetary Disks in σ Orionis," accepted by ApJ.  The raw data can be obtained from the ALMA archive under program IDs 2016.1.00447.S (PI: J. Williams) and 2022.1.00728.S (PI: J. Huang).  Contents images.tar: FITS files of the ALMA continuum images of the eight disks reductionscripts.tar: CASA reduction scripts visibilities.tar: Continuum measurement sets for the eight disks (note that the weights in these measurement sets are not rescaled) 

The Atacama Large Millimeter/submillimeter Array (ALMA) has detected substructures in numerous protoplanetary disks at radii from a few to over 100 au. These substructures are commonly thought to be associated with planet formation, either by serving as sites fostering planetesimal formation or by arising as a consequence of planet–disk interactions. Our current understanding of substructures, though, is primarily based on observations of nearby star-forming regions with mild UV environments, whereas stars are typically born in much harsher UV environments, which may inhibit planet formation in the outer disk through external photoevaporation. We present high-resolution (∼8 au) ALMA 1.3 mm continuum images of eight disks in σ Orionis, a cluster irradiated by an O9.5 star. Gaps and rings are resolved in the images of five disks. The most striking of these is SO 1274, which features five gaps that appear to be arranged nearly in a resonant chain. In addition, we infer the presence of gap or shoulder-like structures in the other three disks through visibility modeling. These observations indicate that substructures robustly form and survive at semimajor axes of several tens of au or less in disks exposed to intermediate levels of external UV radiation as well as in compact disks. However, our observations also suggest that disks in σ Orionis are mostly small, and thus millimeter continuum gaps beyond a disk radius of 50 au are rare in this region, possibly due to either external photoevaporation or age effects. 

ABSTRACT The majority of stars are in binary/multiple systems. How such systems form in turbulent, magnetized cores of molecular clouds in the presence of non-ideal magnetohydrodynamic (MHD) effects remains relatively underexplored. Through athena++-based non-ideal MHD adaptive mesh refinement simulations with ambipolar diffusion, we show that the collapsing protostellar envelope is dominated by dense gravo-magneto-sheetlets, a turbulence-warped version of the classic pseudodisc produced by anisotropic magnetic resistance to the gravitational collapse, in agreement with previous simulations of turbulent, magnetized single-star formation. The sheetlets feed mass, magnetic fields, and angular momentum to a Dense ROtation-Dominated (DROD) structure, which fragments into binary/multiple systems. This DROD fragmentation scenario is a more dynamic variant of the traditional disc fragmentation scenario for binary/multiple formation, with dense spiral filaments created by inhomogeneous feeding from the highly structured larger-scale sheetlets rather than the need for angular momentum transport, which is dominated by magnetic braking. Provided that the local material is sufficiently demagnetized, with a plasma-$$\beta$$ of 10 or more, collisions between the dense spiralling filaments play a key role in facilitating gravitational collapse and stellar companion formation by pushing the local magnetic Toomre parameter $$Q_\mathrm{m}$$ below unity. This mechanism can naturally produce in situ misaligned systems on the 100-au scale, often detected with high-resolution Atacama Large Millimeter Array (ALMA) observations. Our simulations also highlight the importance of non-ideal MHD effects, which affect whether fragmentation occurs and, if so, the masses and orbital parameters of the stellar companions formed. 

ABSTRACT The streaming instability, a promising mechanism to drive planetesimal formation in dusty protoplanetary discs, relies on aerodynamic drag naturally induced by the background radial pressure gradient. This gradient should vary in discs, but its effect on the streaming instability has not been sufficiently explored. For this purpose, we use numerical simulations of an unstratified disc to study the non-linear saturation of the streaming instability with mono-disperse dust particles and survey a wide range of gradients for two distinct combinations of the particle stopping time and the dust-to-gas mass ratio. As the gradient increases, we find most kinematic and morphological properties increase but not always in linear proportion. The density distributions of tightly coupled particles are insensitive to the gradient whereas marginally coupled particles tend to concentrate by more than an order of magnitude as the gradient decreases. Moreover, dust–gas vortices for tightly coupled particles shrink as the gradient decreases, and we note higher resolutions are required to trigger the instability in this case. In addition, we find various properties at saturation that depend on the gradient may be observable and may help reconstruct models of observed discs dominated by streaming turbulence. In general, increased dust diffusion from stronger gradients can lower the concentration of dust filaments and can explain the higher solid abundances needed to trigger strong particle clumping and the reduced planetesimal formation efficiency previously found in vertically stratified simulations. 

ABSTRACT The hunt is on for dozens of protoplanets hypothesized to reside in protoplanetary discs with imaged gaps. How bright these planets are, and what they will grow to become, depend on their accretion rates, which may be in the runaway regime. Using 3D global simulations, we calculate maximum gas accretion rates for planet masses Mp from 1$$\, \mathrm{ M}_{{\oplus }}$$ to $$10\, \mathrm{ M}_{\rm J}$$. When the planet is small enough that its sphere of influence is fully embedded in the disc, with a Bondi radius rBondi smaller than the disc’s scale height Hp – such planets have thermal mass parameters qth ≡ (Mp/M⋆)/(Hp/Rp)3 ≲ 0.3, for host stellar mass M⋆ and orbital radius Rp – the maximum accretion rate follows a Bondi scaling, with $$\max \dot{M}_{\rm p} \propto \rho _{\rm g}M_{\rm p}^2 / (H_{\rm p}/R_{\rm p})^3$$ for ambient disc density ρg. For more massive planets with 0.3 ≲ qth ≲ 10, the Hill sphere replaces the Bondi sphere as the gravitational sphere of influence, and $$\max \dot{M}_{\rm p} \propto \rho _{\rm g}M_{\rm p}^1$$, with no dependence on Hp/Rp. In the strongly superthermal limit when qth ≳ 10, the Hill sphere pops well out of the disc, and $$\max \dot{M}_{\rm p} \propto \rho _{\rm g}M_{\rm p}^{2/3} (H_{\rm p}/R_{\rm p})^1$$. Applied to the two confirmed protoplanets PDS 70b and c, our numerically calibrated maximum accretion rates imply that their Jupiter-like masses may increase by up to a factor of ∼2 before their parent disc dissipates.