Protoplanetary Disks Research Articles

JWST Imaging of Edge-on Protoplanetary Disks. III. Drastic Morphological Transformation Across the Mid-infrared in Oph163131

We present JWST broadband images of the highly inclined protoplanetary disk SSTc2d J163131.2-242627 (Oph163131) from 2.0 to 21 μm. The images show a remarkable evolution in disk structure with wavelength, quite different from previous JWST observations of other edge-on disks. At 2.0 and 4.4 μm, Oph163131 shows two scattering surfaces separated by a dark lane, typical of highly inclined disks. Starting at 7.7 μm, however, (1) the two linear nebulosities flanking the dark lane disappear; (2) the brighter nebula tracing the disk upper surface transitions into a compact central source distinctly larger than the JWST point-spread function and whose intrinsic size increases with wavelength; and (3) patches of extended emission appear at low latitudes, and at surprisingly large radii nearly twice that of the scattered light seen with Hubble Space Telescope and NIRCam, and of the gas. We interpret the compact central source as thermal emission from the star and the inner disk that is not seen directly, but which instead is able to progressively propagate to greater distances at longer wavelengths. The lack of sharp-edged structures in the extended patchy emission argues against the presence of shocks and suggests photoexcitation or stochastic heating of material smoothly flowing away from the star along the disk surface. Finally, the dark lane thickness decreases significantly between 0.6 and 4.4 μm, which indicates that the surface layers of Oph163131 lack grains larger than 1 μm.

Migration of Accreting Planets and Black Holes in Disks

Nascent planets are thought to lose angular momentum (AM) to the gaseous protoplanetary disk via gravitational interactions, leading to inward migration. A similar migration process also applies to stellar-mass black holes (BHs) embedded in the disks of active galactic nuclei. However, AM exchange via accretion onto the planet/BH may strongly influence the migration torque. In this study, we perform 2D global hydrodynamic simulations of an accreting planet/BH embedded in a disk, where AM exchange between the planet/BH and disk via gravity, accretion, pressure, and viscosity are considered. When accretion is turned off, we recover the linear estimate for Type I migration torque. However, for the two planet masses we investigated with our accreting simulations, we find outward migration due to the positive AM deposited onto the accreting body by the disk gas. Our simulations achieve the global steady state for the transport of mass and AM: The mass and AM fluxes are constant across the disk except for jumps ( ΔṀ and ΔJ̇ ) at the planet’s location, and the jumps match the accretion rate and torque on the planet. Our findings suggest that caution is needed when applying the standard results of disk migration to accreting planets and BHs.

Temporal and chromatic variation of polarized scattered light in the outer disk of PDS 70

PDS 70 stands out as the only system hosting a protoplanetary disk and two confirmed planets undergoing formation. It is a unique target for characterizing the dust in this type of disk. We aim to accurately measure the reflected polarized intensity and quantify the variability and asymmetry for PDS 70 across multiple epochs and wavelengths in the optical and near-infrared. We present new high-contrast polarimetric differential imaging observations of PDS 70, with the $N\_R$ filter on SPHERE/ZIMPOL. We combined the new observation with archival data of the VLT/SPHERE instrument, spanning five wavelengths ($N\_R$, $VBB$, $J$, $H$, and $Ks$) over seven epochs and eight years. For each observational epoch, we corrected the smearing effect due to finite instrument resolution, measured the azimuthal brightness profiles, and derived the intrinsic disk-integrated polarized reflectivity and the intrinsic brightness contrasts. With our homogeneous analysis of all available optical and near-infrared data sets of the disk around PDS 70, we find significant temporal variability of the integrated polarized reflectivity as well as the azimuthal brightness profile. This indicates variable shadowing on the outer disk by inner disk structures beyond the resolution limit of current imaging instruments. Despite these variabilities, we observe a systematic wavelength-dependent contrast between the near side and the far side of the inclined disk. These results underline the importance of considering both the shadowing effect from the inner disk and the surface geometry of the observed reflecting disk in the analysis and interpretation of observational data.

Destruction of interstellar methyl cyanide (CH3CN) via collisions with He+⋅ ions

Context. CH3CN (methyl cyanide) is one of the simplest and most abundant interstellar complex organic molecules (iCOMs), and has been detected in young solar analogues, shocked regions, protoplanetary discs, and comets. CH3CN can therefore be considered a key species to explore the chemical connections between the planet-forming disk phase and comets. However, for such comparison to be meaningful, kinetics data for the reactions leading to CH3CN formation and destruction must be updated. Aims. Here we focus on the destruction of methyl cyanide through collisions with He+. . We employed a combined experimental and theoretical methodology to obtain cross sections (CSs) and branching ratios (BRs) as a function of collision energy, from which we calculated reaction rate coefficients k(T) in the temperature range from 10 to 300 K. Methods. We measured CSs and BRs using a guided ion beam setup, and developed a theoretical treatment based on an analytical formulation of the potential energy surfaces (PESs) for the charge exchange process. The method employs a Landau Zener model to obtain reaction probabilities at crossings between the entrance and exit PESs, and an adiabatic centrifugal sudden approximation to calculate CSs and k(T), from subthermal to hyper-thermal regimes. Results. k(T) and experimental BRs differ from those predicted from widely used capture models. In particular, the rate coefficient at 10 K is estimated to be almost one order of magnitude smaller than what is reported in the KIDA database. In addition, the charge exchange is completely dissociative and the most abundant fragments are HCCN+/CCNH+ , HCNH+ and CH2+. Conclusions. Our results, combined with a revised chemical network for the formation of CH3CN, support the hypothesis that methyl cyanide in protoplanetary discs could be mostly the product of gas-phase processes rather than grain chemistry, as currently proposed. These findings are expected to have implications in the comparison of the abundance ratios of N-bearing molecules observed in discs with cometary abundance ratios.

JWST Ice Band Profiles Reveal Mixed Ice Compositions in the HH 48 NE Disk

Planet formation is strongly influenced by the composition and distribution of volatiles within protoplanetary disks. With JWST, it is now possible to obtain direct observational constraints on disk ices, as recently demonstrated by the detection of ice absorption features toward the edge-on HH 48 NE disk as part of the Ice Age Early Release Science program. Here, we introduce a new radiative transfer modeling framework designed to retrieve the composition and mixing status of disk ices using their band profiles, and apply it to interpret the H2O, CO2, and CO ice bands observed toward the HH 48 NE disk. We show that the ices are largely present as mixtures, with strong evidence for CO trapping in both H2O and CO2 ice. The HH 48 NE disk ice composition (pure versus polar versus apolar fractions) is markedly different from earlier protostellar stages, implying thermal and/or chemical reprocessing during the formation or evolution of the disk. We infer low ice-phase C/O ratios around 0.1 throughout the disk, and also demonstrate that the mixing and entrapment of disk ices can dramatically affect the radial dependence of the C/O ratio. It is therefore imperative that realistic disk ice compositions are considered when comparing planetary compositions with potential formation scenarios, which will fortunately be possible for an increasing number of disks with JWST.

Journey of complex organic molecules: Formation and transport in protoplanetary disks

Complex organic molecules serve as indicators of molecular diversity. Their detection on comets, planets, and moons has prompted inquiries into their origins, particularly the conditions conducive to their formation. One hypothesis suggests that the UV irradiation of icy grains in the protosolar nebula generates significant molecular complexity, a hypothesis supported by experiments on methanol ice irradiation. We investigated the irradiation of methanol ice particles as they migrate through the protosolar nebula. Our objective is to ascertain whether the encountered conditions facilitate the formation of complex organics molecules, and we leverage experimental data in our analysis. We developed a two-dimensional model that describes the transport of pebbles during the evolution of the protosolar nebula, employing a Lagrangian scheme. This model computes the interstellar UV flux received by the particles along their paths, which we compared with experimental values. On average, particles ranging from 1 to 100 mu m in size, released at a local temperature of 20 K, undergo adequate irradiation to attain the same molecular diversity as methanol ice during the experiments within timescales of 25 kyr of protosolar nebula evolution. In contrast, 1 cm sized particles require 911 kyr of irradiation to reach similar molecular diversity, making comparable molecular complexity unlikely. Similarly, particles ranging from 1 to 100 mu m in size, released at a local temperature of 80 K, receive sufficient irradiation after 141 and 359 kyr. In contrast, 1 cm sized particles would require several million years to receive this level of irradiation, which is infeasible since they cross the iceline within approximately 500 kyr. The particles readily receive the irradiation dose necessary to generate the molecular diversity observed in the experiments within the outer regions of the disk. Our model, combined with future irradiation experiments, can provide additional insights into the specific regions where the building blocks of planets form.

PRODIGE - envelope to disk with NOEMA. IV. An infalling gas bridge surrounding two Class 0/I systems in L1448N

The formation of stars has been subject to extensive studies in the past decades on scales from molecular clouds to protoplanetary disks. It is still not fully understood how the surrounding material in a protostellar system, which often shows asymmetric structures with complex kinematic properties, feeds the central protostar(s) and their disk(s). We study the spatial morphology and kinematic properties of the molecular gas surrounding the IRS3A and IRS3B protostellar systems in the L1448N region located in the Perseus molecular cloud. We present 1\,mm Northern Extended Millimeter Array (NOEMA) observations of the large program PROtostars DIsks: Global Evolution (PRODIGE). We analyzed the kinematic properties of molecular lines. Because the spectral profiles are complex, the lines were fit with up to three Gaussian velocity components. The clustering algorithm called density-based spatial clustering of applications with noise ( DBSCAN ) was used to disentangle the velocity components in the underlying physical structure. We discover an extended gas bridge (approx 3000\,au) surrounding both the IRS3A and IRS3B systems in six molecular line tracers (C18O, SO, DCN $CO, HC$_ $N, and CH$_ $ toward the IRS3A system. We find that the observed velocity profile is consistent with analytical streamline models of gravitational infall toward IRS3A. The high-velocity C18O ($2-1$) emission toward IRS3A indicates a protostellar mass of approx 1.2\,$M_ odot$. While high angular resolution continuum data often show IRS3A and IRS3B in isolation, molecular gas observations reveal that these systems are still embedded within a large-scale mass reservoir, whose spatial morphology and velocity profiles are complex. The kinematic properties of the extended gas bridge are consistent with gravitational infall toward the protostar IRS3A.

Changing disc compositions via internal photoevaporation

The chemical evolution of protoplanetary discs is a complex process that is not fully understood. Several factors influence the final spatial distribution of atoms and molecules in the disc. One such factor is the inward drift and evaporation of volatile-rich pebbles that can enrich the inner disc with vapour. In particular, the inner disc is first enriched with evaporating water-ice, resulting in a low C/O ratio, before carbon-rich gas from the outer disc – originating from the evaporation of CO, CO2, and CH4 ice – is transported viscously inwards, elevating the C/O ratio again. However, it is unclear how internal photoevaporation – which carries away gas and opens gaps in the disc that can block inward drifting pebbles – affects the chemical composition of the disc. Our goal is to study how and to what extent internal photoevaporation and the subsequent opening of gaps influence the chemical evolution of protoplanetary discs around solar-like stars (M* = 1 M⊙), where we specifically focus on the C/O ratio and the water content. To carry out our simulations, we use a semi-analytical 1D disc model. The code chemcomp includes viscous evolution and heating, pebble growth and drift, pebble evaporation and condensation, as well as a simple chemical partitioning model for the disc. We show that internal photoevaporation plays a major role in the evolution of protoplanetary discs and their chemical composition: As photoevaporation opens a gap, inward drifting pebbles are stopped and can no longer contribute to the volatile content in the gas. In addition, volatile-rich gas from the outer disc, originating from evaporated CO, CO2, or CH4 ice, is carried away by the photoevaporative winds. Consequently, the C/O ratio in the inner disc remains low. In contrast, gaps opened by giant planets still allow the gas to pass, resulting in an elevated C/O ratio in the inner disc, similar to the evolution of viscous discs without internal photoevaporation. This opens the possibility to distinguish observationally between these two scenarios when measuring the C/O ratio, implying that we can infer the root cause of deep gap structures when observing protoplanetary discs. In the case of a clear separation of the disc by photoevaporation, we additionally find an elevated water content in the inner disc, because the water vapour and ice undergo a cycle of evaporation and recondensation, preventing the inward accretion of water onto the star, in contrast to the situation for hydrogen and helium. We conclude that it is very difficult to achieve supersolar C/O ratios in the inner parts of protoplanetary discs when taking internal photoevaporation into account. This indicates the potential importance of photoevaporation for understanding the chemical evolution of these discs and the planets forming in them.

Disc and atmosphere composition of multi-planet systems

In protoplanetary discs, small millimetre-centimetre-sized pebbles drift inwards which can aid in planetary growth and influence the chemical composition of their natal discs. Gaps in protoplanetary discs can hinder the effective inward transport of pebbles by trapping the material in pressure bumps. In this work, we explore how multiple planets change the vapour enrichment by gap opening. For this, we extended the chemcomp code to include multiple growing planets and investigated the effect of 1, 2, and 3 planets on the water content and C/O ratio in the gas disc as well as the final composition of the planetary atmosphere. We followed planet migration over evaporation fronts and found that previously trapped pebbles evaporate relatively quickly and enrich the gas. We also found that in a multi-planet system, the atmosphere composition can be reduced in carbon and oxygen compared to the case without other planets, due to the blocking of volatile-rich pebbles by an outer planet. This effect is stronger for lower viscosities because planets migrate further at higher viscosities and eventually cross inner evaporation fronts, releasing previously trapped pebbles. Interestingly, we found that nitrogen remains super-stellar regardless of the number of planets in the system such that super-stellar values in N/H of giant planet atmospheres may be a tracer for the importance of pebble drift and evaporation.

TriPoD: Tri-Population size distributions for Dust evolution

Context. Dust coagulation and fragmentation impact the structure and evolution of protoplanetary disks and set the initial conditions for planet formation. Dust grains dominate the opacities, they determine the cooling times of the gas via thermal accommodation in collisions, they influence the ionization state of the gas, and the available grain surface area is an important parameter for the chemistry in protoplanetary disks. Therefore, dust evolution is an effect that should not be ignored in numerical studies of protoplanetary disks. Available dust coagulation models are, however, too computationally expensive to be implemented in large-scale hydrodynamic simulations. This limits detailed numerical studies of protoplanetary disks, including these effects, mostly to one-dimensional models. Aims. We aim to develop a simple – yet accurate – dust coagulation model that can be easily implemented in hydrodynamic simulations of protoplanetary disks. Our model shall not significantly increase the computational cost of simulations and provide information about the local grain size distribution. Methods. The local dust size distributions are assumed to be truncated power laws. Such distributions can be fully characterized by only two dust fluids (large and small grains) and a maximum particle size, truncating the power law. We compare our model to state- of-the-art dust coagulation simulations and calibrate it to achieve a good fit with these sophisticated numerical methods. Results. Running various parameter studies, we achieved a good fit between our simplified three-parameter model and DustPy, a state-of-the-art dust coagulation software. Conclusions. We present TriPoD, a sub-grid dust coagulation model for the PLUTO code. With TriPoD, we can perform twodimensional, vertically integrated dust coagulation simulations on top of a hydrodynamic simulation. Studying the dust distributions in two-dimensional vortices and planet-disk systems is thus made possible.

MANTA-Ray: Supercharging speeds for calculating the optical properties of fractal aggregates in the long-wavelength limit

Abstract Correctly modelling the absorptive properties of dust and haze particles is of great importance for determining the abundance of solid matter within protoplanetary disks and planetary atmospheres. Rigorous analyses such as the discrete dipole approximation (DDA) can be used to obtain accurate absorption cross-sections, but these require significant computing time and are often impractical to use in models. A simple analytical equation exists for spherical particles in the long-wavelength limit (where the wavelength is much larger than the size of the dust particle), but we demonstrate that this can significantly underestimate the absorption. This effect is found to depend strongly on refractive index, with values of m = 1 + 11i corresponding to an underestimate in absorption by a factor of 1,000. Here we present MANTA-Ray (Modified Absorption of Non-spherical Tiny Aggregates in the RAYleigh regime): a simple model that can calculate absorption efficiencies within 10-20% of the values predicted by DDA, but 1013 times faster. MANTA-Ray is very versatile and works for any wavelength and particle size in the long wavelength regime. It is also very flexible with regards to particle shape, and can correctly model structures ranging from long linear chains to tight compact clusters, composed of any material with refractive index 1+0.01i ≤m ≤ 11+11i. The packaged model is provided as publicly-available code for use by the astrophysical community.

Running with the bulls

Context. Stars and planets form in regions of enhanced stellar density, subjecting protoplanetary discs to gravitational perturbations from neighbouring stars. Observations in the Taurus star-forming region have uncovered evidence of at least three recent, star-disc encounters that have truncated discs (HV/DO Tau, RW Aurigae, and UX Tau), raising questions about the frequency of such events. Aims. We aim to assess the probability of observing truncating star-disc encounters in Taurus. Methods. We generated a physically motivated dynamical model including binaries and a spatial-kinematic substructure to follow the historical dynamical evolution of the Taurus star-forming region. We used this model to track star-disc encounters and the resulting outer disc truncation over the lifetime of Taurus. Results. A quarter of discs are truncated below 30 au by dynamical encounters, but this truncation mostly occurs in binaries over the course of a few orbital periods, on a timescale ≲0.1 Myr. Nonetheless, some truncating encounters still occur up to the present age of Taurus. Strongly truncating encounters (ejecting ≳10 percent of the disc mass) occur at a rate ∼10 Myr−1, sufficient to explain the encounter between HV and DO Tau ∼0.1 Myr ago. If encounters that eject only ∼1 percent of the disc mass are responsible for RW Aurigae and UX Tau, then they are also expected with encounter rate Γenc ∼ 100–200 Myr−1. However, the observed sample of recent encounters is probably incomplete, since these examples occurred in systems that are not consistent with a random drawing from the mass function. One more observed example would statistically imply additional physics, such as replenishment of the outer disc material. Conclusions. The marginal consistency of the frequency of observed recent star-disc encounters with theoretical expectations underlines the value of future large surveys searching for external structures associated with recent encounters. The outcome of such a survey offers a highly constraining, novel probe of protoplanetary disc physics.

Dynamical Consequence of Shadows Cast to the Outer Protoplanetary Disks. I. Two-dimensional Simulations

There has been increasing evidence of shadows from scattered light observations of outer protoplanetary disks (PPDs) cast from the (unresolved) disk inner region, while in the meantime these disks present substructures of various kinds in the submillimeter. As stellar irradiation is the primary heating source for the outer PPDs, the presence of such shadows thus suggests inhomogeneous heating of the outer disk in azimuth, leading to a “thermal forcing” with dynamical consequences. We conduct a suite of idealized two-dimensional disk simulations of the outer disk with azimuthally varying cooling prescription to mimic the effect of shadows, generally assuming the shadow is static or slowly rotating. The linear response to such shadows is two-armed spirals with the same pattern speed as the shadow. Toward the nonlinear regime, we find that shadows can potentially lead to the formation of a variety of types of substructures including rings, spirals, and crescents, depending on viscosity, cooling time, etc. We have conducted systematic and statistical characterization of the simulation suite, and as thermal forcing from the shadow strengthens, the dominant form of shadow-induced disk substructures change from spirals to rings, and eventually to crescents/vortices. Our results highlight the importance of properly modeling the dynamical impact of inhomogeneous stellar irradiation, while calling for more detailed modeling incorporating more realistic disk physics.

Radial transport and nebular thermal processing of millimeter‐sized solids in the Solar protoplanetary disk inferred from Cr‐Ti‐O isotope systematics of chondrules

AbstractUnderstanding the material transport and mixing processes in the Solar protoplanetary disk provides important constraints on the origin of chemical and isotopic diversities of our planets. The limited extent of radial transport and mixing between the inner and outer Solar System has been suggested based on a fundamental isotopic dichotomy between non‐carbonaceous (NC) and carbonaceous (CC) meteorite groups. The limited transport and mixing could be further tested by tracing the formation regions of individual meteoritic components, such as Ca‐Al‐rich inclusions (CAIs) and chondrules. Here, we show further evidence for the outward transport of CAIs and chondrules from the inner and subsequent thermal processing in the outer region of the protoplanetary disk based on the petrography and combined Cr‐Ti‐O isotope systematics of chondrules from the Vigarano‐like (CV) carbonaceous chondrite Allende. One chondrule studied consists of an olivine core that exhibits NC‐like Ti and O, but CC‐like Cr isotopic signatures, which is enclosed by a pyroxene igneous rim with CC‐like O isotope ratios. These observations indicate that the olivine core formed in the inner Solar System. The olivine core then migrated into the outer Solar System and experienced nebular thermal processing that generated the pyroxene igneous rim. The nebular thermal processing would result in Cr isotope exchange between the olivine core and CC‐like materials, but secondary alteration effects on the parent body are also responsible for the CC‐like Cr isotope signature. By combining previously reported Cr‐Ti‐O isotope systematics of CV chondrules, we show that some CV chondrules larger than ~1 mm would have formed in the inner Solar System. The accretion of the millimeter‐sized, inner Solar System solids onto the CV carbonaceous chondrite parent body would require their very early migration into the outer Solar System within the first 1 million years after the Solar System formation.

How external photoevaporation changes the chemical composition of the inner disc

Stars mostly form in cluster environments, where neighbouring stars can have an influence on the evolution of the newly formed protoplanetary discs. Besides gravitational interactions, external photoevaporation can also shape protoplanetary discs. Depending on the strength of external photo-evaporation, discs may be destroyed within 1–2 Myrs, or more gradually, depending on whether the external photo-evaporation field is stronger or weaker, respectively. We used the chemcomp code, which includes a viscous disc evolution model including pebble drift and evaporation to calculate the chemical composition of protoplanetary discs. We extended this code to include external photoevaporation following the FRIED grid. Before external photoevaporation becomes efficient, the disc follows a purely viscous disc evolution, where the C/O ratio in the inner disc initially decreases due to inwardly drifting and evaporating water ice pebbles. Over time, the C/O ratio increases again as water vapour is accreted onto the star and carbon-rich gas gradually migrates inwards. However, once external photo-evaporation commences, the outer disc begins to get dispersed. During this process, the inner disc’s chemical evolution still follows the evolution of a purely viscous disc because the majority of the pebbles have already drifted inwards on timescales shorter than 1 Myr. At low viscosity, the inner disc’s C/O ratio remains sub-solar until the disc is dispersed through external photoevaporation. At a high viscosity, the inner disc’s composition can reach super-solar values in C/O, because the water vapour is accreted onto the star faster and carbon rich gas from the outer disc can move inwards faster as well, as long as the disc can survive a few Myrs. In both cases, there is no visible difference in terms of the chemical composition of the inner disc compared to a purely viscous model, due to the rapid inward drift of pebbles that sets the chemical composition of the disc. Thus, our model predicts that the inner disc chemistry would be similar between discs that are subject to external photoevaporation and discs that are isolated and experience no external photo-evaporation. This finding is in line with observations of protoplanetary discs with JWST.

Multiwavelength high-resolution polarimetric imaging of second-generation disc around post-AGB binary IRAS 08544–4431 with SPHERE

ABSTRACT Exploring the formation and evolution of second-generation circumbinary discs around evolved binary stars, such as post-asymptotic giant branch (post-AGB) and post-red giant branch binaries, provides valuable insights into the complex binary interaction process that concludes the red-giant phase of evolution in these systems. Additionally, it offers a novel opportunity to investigate the formation of second-generation planets within dusty discs surrounding evolved stars. We present a pilot multiwavelength polarimetric imaging study of the post-AGB binary system IRAS 08544–4431 using the European Southern Observatory–Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet Research (VLT/SPHERE) instrument. This study is focused on optical V- and $I^{\prime }$-band Zurich Imaging Polarimeter (ZIMPOL) data to complement near-infrared (near-IR) H-band IRDIS data presented previously. The study aims to investigate the dust scattering properties and surface morphology of the post-AGB circumbinary disc as a function of wavelength. We successfully resolved the extended disc structure of IRAS 08544–4431, revealing a complex disc morphology, high polarimetric disc brightness (up to $\sim$1.5 %), and significant forward scattering at optical wavelengths. Additionally, we found that the disc shows a grey polarimetric colour in both optical and near-IR. The findings highlight similarities between post-AGB circumbinary discs and protoplanetary discs, suggesting submicron-sized porous aggregates as the dominant surface dust composition, and indicating potential warping within the disc. However, further expansion of the multiwavelength analysis to a larger sample of post-AGB binary systems, as well as high-resolution observations of dust continuum and gas emission, is necessary to fully explore the underlying structure of post-AGB circumbinary discs and associated physical mechanisms.

Origin of transition disk cavities: Pebble-accreting protoplanets vs super-Jupiters

Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can create the appearance of cavities in the dust disk. We evolve the disks with low-mass growing embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos' orbits. We vary the planet and disk properties to understand the resulting dust profile. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is $10^ $. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities and distinct ring-like structures near planet orbits. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations.

Thousands of planetesimals: Simulating the streaming instability in very large computational domains

The streaming instability is a mechanism whereby pebble-sized particles in protoplanetary discs spontaneously come together in dense filaments, which collapse gravitationally to form planetesimals upon reaching the Roche density. The extent of the filaments along the orbital direction is nevertheless poorly characterised, due to a focus in the literature on small simulation domains where the behaviour of the streaming instability on large scales cannot be determined. We present here computer simulations of the streaming instability in boxes with side lengths up to $6.4$ scale heights in the plane. This is $32$ times larger than typically considered simulation domains and nearly a factor $1,000$ times the volume. We show that the azimuthal extent of filaments in the non-linear state of the streaming instability is limited to approximately one gas scale height. The streaming instability will therefore not transform the pebble density field into axisymmetric rings; rather the non-linear state of the streaming instability appears as a complex structure of loosely connected filaments. Including the self-gravity of the pebbles, our simulations form up to $4,000$ planetesimals. This allows us to probe the high-mass end of the initial mass function of planetesimals with much higher statistical confidence than previously. We find that this end is well-described by a steep exponential tapering. Since the resolution of our simulations is moderate -- a necessary trade-off given the large domains -- the mass distribution is incomplete at the low-mass end. When putting comparatively less weight on the numbers at low masses, at intermediate masses we nevertheless reproduce the power-law shape of the distribution established in previous studies.

Ethanolamine ices: Experiments in simulated space conditions

Laboratory experiments on the interactions between complex organic molecules, interstellar dust, and ultraviolet (UV) radiation are crucial to understanding the physicochemical mechanisms that lead to the synthesis of the observed interstellar complex organic molecules (iCOMs), and to search for new molecular species not yet observed in the gas phase of the interstellar medium (ISM). We aim to study the role of a new, recently discovered interstellar molecule, ethanolamine (EtA, NH CH CH OH), in surface chemistry in the ISM. In the laboratory, thanks to a combination of temperature programmed desorption (TPD) experiments and electron ionization (EI) mass spectrometry analyses, we studied the thermal desorption of pure ethanolamine and its mixture with water from nanometric amorphous olivine grains cooled down to 10 K, with or without UV irradiation. Ethanolamine was found to be stable, even in the presence of water, when irradiated with UV light. The presence of olivine grains strongly modified the TPD curves, trapping the molecule up to about 295 K, meaning that the precursors of some biological molecules could be retained on the grains even in the innermost parts of protoplanetary disk. We then identified a series of products formed when the molecule was irradiated onto the dust substrate. Of particular interest is the fact that irradiation of ice containing ethanolamine, a molecule known to be present in the ISM, can produce more complex and astrobiologically interesting species. Furthermore, our results further our understanding of existing observational data.

Volatile composition of the HD 169142 disk and its embedded planet

Abstract The composition of a planet’s atmosphere is intricately linked to the chemical makeup of the protoplanetary disk in which it formed. Determining the elemental abundances from key volatiles within disks is therefore essential for establishing connections between the composition of disks and planets. The disk around the Herbig Ae star HD 169142 is a compelling target for such a study due to its molecule-rich nature and the presence of a newly-forming planet between two prominent dust rings. In this work, we probe the chemistry of the HD 169142 disk at small spatial scales, drawing links between the composition of the disk and the planet-accreted gas. Using thermochemical models and archival data, we constrain the elemental abundances of volatile carbon, oxygen, and sulfur. Carbon and oxygen are only moderately depleted from the gas phase relative to their interstellar abundances, with the inner ~60 au appearing enriched in volatile oxygen. The C/O ratio is approximately solar within the inner disk (~0.5) and rises above this in the outer disk (>0.5), as expected across the H2O snowline. The gas-phase sulfur abundance is depleted by a factor of ~1000, consistent with a number of other protoplanetary disks. Interestingly, the observed SiS emission near the HD 169142 b protoplanet vastly exceeds chemical model predictions, supporting previous hypotheses suggesting its origin in shocked gas or a localised outflow. We contextualise our findings in terms of the potential atmospheric composition of the embedded planet, and highlight the utility of sulfur-bearing molecules as probes of protoplanetary disk chemistry.