EXOA12 | Protoplanetary disks and planetesimal formation


Protoplanetary disks and planetesimal formation
Co-organized by SB
Convener: Raphael Marschall | Co-conveners: Joanna Drazkowska, Manuela Lippi, Jessica Barnes, Til Birnstiel, Sébastien Charnoz, Martin Cordiner, Marjorie Galinier, Aurelie Guilbert-Lepoutre, Anders Johansen, Kundan Kadam, Hubert Klahr, Tim Lichtenberg, Cyrielle Opitom, Linda Podio, Giovanni Rosotti, Jacob Simon, Colin Snodgrass, Catherine Walsh
| Thu, 12 Sep, 10:30–12:00 (CEST), 14:30–18:00 (CEST)|Room Neptune (Hörsaal D)
| Attendance Fri, 13 Sep, 10:30–12:00 (CEST) | Display Fri, 13 Sep, 08:30–19:00
Orals |
Thu, 10:30
Fri, 10:30
Understanding the formation and evolution of the earliest phase of planet formation - the disk phase - is crucial to planetary science. Over the past decade, significant progress has been made in observing protoplanetary disks, understanding the gas and dust dynamics, their chemical composition, and forming the first gravitationally-bound bodies therein, called planetesimals. The planetesimals are precursors of today's asteroids and comets. Thus, the Solar System provides important constraints from the architecture and chemistry of small body populations (asteroids, comets, Kuiper-belt objects) and the meteorites. These measurements inform when and where planetesimals formed and how they might have evolved. Thus, they are critical to constraining the Solar System and planet formation models more generally.
In this session, we welcome contributions on the following topics:
1) observations of disks and their properties,
2) theoretical models of disks (their formation and evolution),
3) models of planetesimal formation and evolution (thermal, collisional, dynamical, etc.),
4) links between planetesimals, small bodies (asteroids, comets, KBOs, etc.), meteorites, and samples returned by space missions.
5) links between the chemical composition of small bodies and that of ices and gas in protoplanetary disks
This interdisciplinary session will serve as a platform to exchange recent results regarding all of the aspects of planetesimal formation in the proto-solar and other protoplanetary disks. We look to build synergy between astrochemistry, star and planet formation models, cosmochemistry, and Solar System research.

Orals: Thu, 12 Sep | Room Neptune (Hörsaal D)

Chairpersons: Joanna Drazkowska, Til Birnstiel
On-site presentation
Luca Delussu, Tilman Birnstiel, Anna Miotello, Paola Pinilla, Giovanni Rosotti, and Sean Andrews

Large mm surveys of star-forming regions enable the study of entire populations of planet-forming disks and reveal correlations between their observable properties. The ever-increasing number of these surveys has led to a flourishing of population study, a valuable tool and approach that is spreading in ever more fields. Population studies of disks have shown that the correlation between disk size and millimeter flux could be explained either through disks with strong substructure, or alternatively by the effects of radial inward drift of growing dust particles.


In this study we performed a population synthesis of the continuum emission of disks varying the initial conditions of the disk and substructure to constrain the parameters and initial conditions of planet-forming disks and address the question of the need for the presence of substructures in disks and, if needed, their predicted characteristics to best reproduce the observed distributions of disk sizes, millimeter fluxes, and spectral indices available.


We showed that observed distributions of spectral indices, sizes, and luminosities together can be best reproduced by disks with significant substructure, namely a perturbation strong enough to be able to trap particles, and that is formed early in the evolution of the disk. Agreement is reached by relatively high initial disk masses and moderate levels of turbulence. Only opacities with high absorption efficiency can reproduce the observed spectral indices. Our results extend to the whole population that substructure is likely ubiquitous, so far assessed only in individual disks and implies that most "smooth" disks hide unresolved substructure.

How to cite: Delussu, L., Birnstiel, T., Miotello, A., Pinilla, P., Rosotti, G., and Andrews, S.: Population Synthesis Models Indicate a Need for Early andUbiquitous Disk Substructures, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-66, https://doi.org/10.5194/epsc2024-66, 2024.

On-site presentation
Xiaoyi Ma and Ruobing Dong

The HD34282 is a protoplanetary disk that hosts an azimuthal asymmetry in the mm dust continuum observed by ALMA. The asymmetry coincides with a one-arm spiral and shadow on the outer disk in near-infrared scattered light, which is coherent with signatures of a vortex shown in simulations. HD34282 thus one of few disks with solid evidence for the presence of a vortex in both NIR and mm observations. The presence of vortices is key to planet formation since they are prime sites to form planetesimals and the potential birthplace of the planets. In our work, we aim to further test the vortex hypothesis for HD34282 by examining two additional theoretical predictions for vortices: i) smaller dust traced at shorter wavelengths is less concentrated azimuthally than larger dust traced at longer wavelengths; ii) dust at the vortex center can reach a maximum dust size of several mm, one order of magnitude or larger than that in the background rings. This is done by carrying out high-resolution multi-wavelength dust continuum observations. We will compare the azimuthal extent of the structure at multiple wavelengths and constrain the dust properties via multi-wavelength spectral energy distribution modelling. Once two predictions are verified, this project will have the potential to provide the most definitive verification of a vortex in a protoplanetary disk and associate the azimuthal asymmetries mm continuum observation with vortices. On the other hand, the negative result would challenge the current theory and motivate alternative explanations for both azimuthal asymmetries in the mm continuum and one-arm spirals in NIR.

How to cite: Ma, X. and Dong, R.: Testing the vortex hypothesis in a protoplanetary disk, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-111, https://doi.org/10.5194/epsc2024-111, 2024.

On-site presentation
Nathan Magnan, Tobias Heinemann, and Henrik Latter

A major hurdle in planet formation theory is that we do not understand how pebbles congregate into planetesimals. A promising way to overcome this metre-scale barrier involves a mechanism called the streaming instability (SI). This hydrodynamic instability gathers the pebbles into clumps so dense that they collapse gravitationally and form planetesimals.

Unfortunately, the mechanism responsible for the onset of this instability remains mysterious. This makes it hard to evaluate the value of the SI as a planetesimal formation theory: how robust is the mechanism, how does it saturate, etc.

Fortunately, some significant progress has been made recently: J. Squire and P. Hopkins showed that the SI is a Resonant Drag Instability (RDI) involving inertial waves. In the first part of this talk, we build on their insight to produce a clear physical picture of how the SI develops.

Like all RDIs, the SI is built on a feedback loop: in the ‘forward action’, an inertial wave concentrates pebbles into clumps; in the ‘backward reaction’, those drifting pebble clumps excite an inertial wave. Each process breaks into two mechanisms, a fast one and a slow one. At resonance, each forward mechanism can couple with a backward mechanism to close a feedback loop. Unfortunately, the fast-fast loop is stable, so the SI uses the fast-slow and slow-fast loops. Despite this last layer of complexity, we hope that our explanation will help understand how the SI works, in which conditions it can grow, how it manifests itself, and how it saturates.

Another problem is that the SI can only develop in regions containing a high density of similar-sized pebbles. Those conditions are met in large-scale vortices, but no one knows if the SI can feed on vorticial flows. Indeed, each instability can only grow in a few specific flows, and a priori the SI is active in Keplerian flows, not vortex flows. We answer this long-standing question in the second part of the talk.

To do so, we develop a simple pen-and-paper model of a pebble-laden vortex in a protoplanetary disc. We find that if the vortex is weak and anticyclonic, pebbles drift towards its centre. We then build a vortex analog of the shearing box to analyse the local linear stability of our pebble-laden vortex. We find that the pebbles’ drift powers an instability which closely resembles the SI. Indeed, both rely on the same resonance between the pebble drift and inertial waves. This result strengthens the case for vortex-induced planetesimal formation.

How to cite: Magnan, N., Heinemann, T., and Latter, H.: The physical mechanism of the streaming instability, and whether it works in vortices, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-464, https://doi.org/10.5194/epsc2024-464, 2024.

On-site presentation
Ben Schubert, Jürgen Blum, Ingo von Borstel, Rainer Schräpler, Noah Molinski, Adrian Pöppelwerth, Matthias Isensee, Thilo Glißmann, Daniyar Balapanov, and Andrei Vedernikov

Protoplanetary disks (PPDs), the cradles of planetary systems around young stars, are composed of dust and ice particles immersed in a rarefied gas. These grains possess initial sizes of less than and up to about 1 µm and collide due to Brownian motion, drift motions relative to the gas, and gas turbulence. Provided that the collision velocity remains below a threshold value, grains stick upon first contact and form fractal agglomerates with typical fractal dimensions just below 2. This is the case for collisions caused by Brownian motion, which occur at thermal velocity.

The ICAPS experiment (Interactions in Cosmic and Atmospheric Particle Systems) studies these collisions and growth processes under micogravity conditions. To avoid gravity-induced sedimentation and compaction of the agglomerates, the experiment flew on board of the TEXUS-56 and TEXUS-58 sounding rockets. Monomeric, spherical SiO2 dust (1.5 µm in diameter) was injected into a vacuum chamber at ~107 times the number density in PPDs, reducing processes that take ~100 years in nature to a few minutes. A specially designed thermal trap was used to stabilize the dust cloud and center it in the fields of view of two perpendicular overview cameras. Further in-situ observations were made with a high-speed camera attached to a long-distance microscope (LDM, see Fig. 1 for example agglomerates). An electrical field was repeatedly applied to measure particle charges that diminish drastically within the first ~20 seconds of experiment time due to neutralizing collisions (see Fig. 2).

Fig. 1: Collage of 190 agglomerates cropped from LDM images (flat-field corrected and inverted).

Fig. 2: Temporal evolution of particle charging of the four experimental runs. The mean charge per monomer is shown in gray and the standard deviation is shown in black. Only the more frequent measurements from the second flight of ICAPS (denoted as SR2) reveal the speed at which the charge is neutralized.

With the high spatial and temporal resolution of the LDM and high-speed camera, it was possible to analyze the Brownian motion and rotation of a great number of particles, yielding their masses, moments of inertia, as well as translational and rotational friction times. From these data, an ensemble fractal dimension of 1.4 could be derived (see Schubert et al. 2023). Careful cross-calibration of the cameras also allowed for mass-frequency distributions of the whole dust cloud to be obtained from the overview cameras, taking into account the cloud morphology. In one out of the four experimental runs, the cloud volume shrank slowly but significantly due to a subtle, thermal anomaly (see Fig. 3), which, combined with a conserved total mass, lead to the runaway growth (or gelation) of a few oligarch agglomerates. These agglomerates clearly detach from the otherwise self-similar mass-frequency distributions (see Schubert et al. 2024 and Fig. 4).

Fig. 3: Shrinking cloud volume across 124 seconds due to a subtle, thermal anomaly in one of the experimental runs (from Schubert et al. 2024).

Fig. 4: Mass-frequency distributions of six consecutive experimental sequences (with subtle thermal anomaly), where N is the number of constituent monomers (from Schubert et al. 2024).

 We modeled the ensemble growth of each of the four experimental runs using a mean-field approximation as well as a Monte-Carlo simulation. The former is based on a version of Smoluchowski's coagulation equation that reads

Here, n, K0, N, and κ are the number density, a pre-factor, the mean number of monomers, and an exponent, respectively. The exponent is κ ≈ -0.3 for diffusive agglomeration of fractal aggregates in the free molecular flow limit, whereas it becomes κ ≈ 0.5 in the ballistic regime. A formal fit of the solution of the above equation yields κ = 0.236 with the thermal anomaly and κ = 0.350 without, which suggest that the growth is relatively close to the pure ballistic Brownian limit (see Schubert et al. 2024 and Fig. 5).

Fig. 5: Temporal evolution of the frame-wise mean and maximum mass, given as the number of constituent monomers, from the first flight of ICAPS (TEXUS-56), modelled with a mean-field approximation. Data from the first experimental run (thermal anomaly) are denoted in black and those from the second run are shown in gray (from Schubert et al. 2024).


[Schubert et al. 2023] Schubert, B., Molinski, N., Borstel, I., Glißmann, T., Balapanov, D., Vedernikov, A., & Blum, J. (2023). Brownian translation and rotation from the ballistic to the diffusive limit and derivation of the physical properties of dust agglomerates. Phys. Rev. E, 107, 034136. DOI: 10.1103/PhysRevE.107.034136

[Schubert et al. 2024] B. Schubert, J. Blum, M. Isensee, N. S. Molinski, A. Pöppelwerth, I. von Borstel, R. Schräpler, D. Balapanov, & A. Vedernikov (2024). The formation of large aggregates by Brownian growth and the onset of a runaway process. Europhysics Letters, 145(3), 30001. DOI: 10.1209/0295-5075/ad2340

How to cite: Schubert, B., Blum, J., von Borstel, I., Schräpler, R., Molinski, N., Pöppelwerth, A., Isensee, M., Glißmann, T., Balapanov, D., and Vedernikov, A.: Observation of Dust Particle Collisions and Growth under Microgravity Conditions, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-678, https://doi.org/10.5194/epsc2024-678, 2024.

On-site presentation
Jürgen Blum, Coskun Aktas, Matthias Isensee, Andreas Bodenstein, Ben Schubert, and Noah Molinski

In a novel experimental setup, we studied the growth of dust aggregates for an extended period of time under realistic protoplanetary conditions, i.e. in a rarefied gas and for relative sedimentation of the grains with velocities on the order of 1 cm/s. We observed a rapid growth of fractal aggregates consisting of µm-sized silica grains and measured their mass spectra as a function of time. Sampling of the aggregates allowed a better characterization of the fractal structure than in-situ observations. We also performed Monte Carlo simulations of the growth process, including explicit collisions, and could achieve a good match to our laboratory observations. Our mean-field model of the growth process is in agreement with the experimental findings and predicts an exponentially fast growth for fractal aggregates (whose collision cross sections are proportional to their mass and whose gas-grain response times are mass-independent), as long as mass loss of the system is negligible. For systems with mass loss, a maximum aggregate mass can be predicted. Our results are directly applicable to the study of dust-aggregate growth in protoplanetary disks, in particular for (but not restricted to) the sedimentation/drift stage before the onset of restructuring. 

How to cite: Blum, J., Aktas, C., Isensee, M., Bodenstein, A., Schubert, B., and Molinski, N.: Exponentially fast growth of dust aggregates during the sedimentation/drift stage, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-7, https://doi.org/10.5194/epsc2024-7, 2024.

On-site presentation
Florence Chioma Onyeagusi, Jens Teiser, and Gerhard Wurm

In planet formation, the evolution of particles from dust to km-sized planetesimals goes through different stages of growth processes [1]. Starting with micron dust, hit-and-stick collisions create rather fluffy aggregates. With further collisions, these aggregates become more compact until the kinetic energy cannot dissipate into deformation anymore. At about mm-size, the dust aggregates reach the so-called bouncing barrier, where further growth is halted [2]. However, for subsequent growth mechanisms (e.g. hydrodynamic trapping through streaming instability) to set in, cm- to dm-sized pebbles are needed [3]. There are several approaches and explanations how one could overcome the bouncing barrier. One of them is collisional charging. Through tribocharging, there will be a transfer of electric charges between particles with each impact, leaving surface charges at the point of contact [4,5]. In previous experiments, these surface charges have already proven to be the cause of stable cluster formation for solid, monolithic grains [6]. Now, for the very first time, we also observed clustering of charged dust aggregates.

We conducted microgravity experiments at the Drop Tower in Bremen with mm and sub-mm aggregates made from µm dust. The sample is placed in an experiment cell under vacuum conditions. During the 9 seconds of microgravity, the cell can be shaken to distribute the sample and induce inter-particle collisions. The video data show that the particles move rather randomly through the volume of the cell. For the sub-mm aggregates, clusters already form during the shaking phase. For the mm particles, the clustering only begins as soon as the shaking stops and the granular gas has somewhat cooled down. Both samples form cm-sized clusters, the smaller particles more efficiently than the larger ones. The clusters are stable when colliding with the wall but can be eroded by particle impacts at certain velocities. When an electric field is applied to the chamber walls, single particles and small clusters are accelerated to the walls, indicating that they are electrically charged.

Our findings show that electric charges are capable of bridging the bouncing barrier. Sub-mm and mm particles that are made up of µm grains will stick together after impacts below a certain velocity, forming cm-clusters that are mostly stable against further impacts. This paves the way for pebbles to grow to a size range where further growth processes set in, eventually leading to km-sized planetesimals that can accrete more mass gravitationally.


[1]           G. Wurm, J. Teiser, 2021, Nature Reviews Physics, Vol. 3, No. 6, Springer Science and Business Media LLC, p. 405-421

[2]           A. Zsom, C. W. Ormel, C. Güttler, J. Blum, C. P. Dullemond, 2010, Astronomy & Astrophysics, 513, A57

[3]           A. Johansen, H. Klahr, T. Henning, 2006, The Astrophysical Journal, Vol. 636, No. 2, American Astronomical Society, p. 1121-1134

[4]           D. J. Lacks, T. Shinbrot, 2019, Nature Reviews Chemistry, Vol. 3, No. 8, Springer Science and Business Media LLC, p. 465-476

[5]           T. Steinpilz, F. Jungmann, K. Joeris, J. Teiser, G. Wurm, Gerhard, 2020, New Journal of Physics, Vol. 22, No. 9, IOP Publishing, p. 093025

[6]           J. Teiser, M. Kruss, F. Jungmann, G. Wurm, 2021, The Astrophysical Journal, 908, L22

How to cite: Onyeagusi, F. C., Teiser, J., and Wurm, G.: From Dust Till Dawn – How Dust Aggregates grow to Planetesimals with Tribocharging, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-531, https://doi.org/10.5194/epsc2024-531, 2024.

On-site presentation
Laurent Schönau, Jens Teiser, and Gerhard Wurm

Wind erosion is a serious threat to the evolution of planetesimals in the early stages of planet formation. Since they move around the star at a different orbital velocity than the surrounding gas, they feel a permanent headwind of at least 50 m/s [1]. In the case of eccentric orbits, this difference in velocity can increase significantly. Planetesimals are not solid rocks, but rather a collection of loosely bound dust aggregates [2] that are held together by the low self-gravity. Although the pressure in protoplanetary disks is very low, wind erosion can dismantle planetesimals. As a result, their existence is ruled out in some areas close to the star [3,4].

In a series of wind tunnel experiments in the laboratory and on microgravity platforms such as the drop tower Bremen and parabolic flights, we have recreated the conditions on planetesimals more and more realistically. Under pressures down to 1 Pa and gravity down to 10-5g, we observed and analysed wind-induced erosion of granular particles. Starting with simple glass spheres, we finally recreated the surface of a pebble pile planetesimal with millimetre sized SiO2 dust aggregates. These aggregates were produced by the collision of micrometre sized SiO2 particles in analogy to the dust growth up to the bouncing barrier in protoplanetary disks.

As a result of our experiments, we found a single formula that predicts the erosion threshold of granular particles on the surface of a planetesimal. Its overall size, the volume and density of the pebbles forming it and its position in the protoplanetary disk can be set as parameters. Together with a suitable disk model, this allows us to define stable and unstable orbits for the evolution of planetesimals into full grown planets.



[1]        Weidenschilling S. J., 1977, MNRAS, 180, 57

[2]        Wahlberg Jansson K., Johansen A., Bukhari Syed M., Blum J., 2017, ApJ, 835, 109

[3]        Cedenblad L., Schaffer N., Johansen A., Mehlig B., Mitra D., 2021, ApJ, 921, 123

[4]        Schönau, L., Teiser, J., Demirci, T., Joeris, K., Onyeagusi, F.C., Fritscher, M., Wurm, G., 2023, A&A, 672 A169

How to cite: Schönau, L., Teiser, J., and Wurm, G.: One formula to describe the struggle between planetesimals and gas drag: Insights from microgravity experiments, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-522, https://doi.org/10.5194/epsc2024-522, 2024.

Lunch break
Chairpersons: Manuela Lippi, Cyrielle Opitom
On-site presentation
Planetesimal gravitational collapse in gaseous environment: thermal and dynamic evolution
Paul Segretain, Héloïse Méheut, and Manuel Moreira
On-site presentation
Nerea Gurrutxaga, Joanna Drazkowska, and Thorsten Kleine

Carbonaceous chondrites are some of the most primitive meteorites in our Solar System. They contain refractory inclusions, chondrules, and CI chondrite-like matrix, and originate from planetesimals accreted a few Myr after Solar System formation started. Recent work by Hellmann et al. (2023) showed that there is a fundamental link between the abundances of chondrules and Calcium-Aluminum-rich Inclusions (CAIs), highlighting their abundance is correlated in carbonaceous chondrites. Furthermore, their findings suggest a direct correlation between the abundance of fine-grained dust (i.e., matrix) within carbonaceous chondrites and the accretion time of their parent bodies. They proposed that variations in these abundances reflect the entrapment of CAIs and chondrule precursors within pressure maxima in the protoplanetary disk, likely associated with the gap opened during the formation of Jupiter.

Motivated by these findings, we employ Monte Carlo simulations of dust evolution to explore the plausibility of carbonaceous chondrite parent body formation in the outer regions of a Jupiter-induced gap. Our investigation includes various collision models between refractory inclusions, chondrules and matrix-like materials. At high gas densities, small dust is well-coupled to the gas and can cross the gap, softening the barrier between outer and inner Solar System materials. However, we show that less fragmentation-prone refractory inclusions and chondrules may not leak through the gap. Therefore, their abundance increases in the outer regions (see Figure 1, left panel). As the gas disperses over time, small dust decouples from the gas and gets trapped outside the gap, reducing the previous enrichment of refractory inclusions and chondrules (see Figure 1, right panel). Under favourable conditions for triggering streaming instability, it is possible to reproduce the formation of carbonaceous chondrite parent bodies rich in refractory inclusions and chondrules while their abundance decreases over time.

This scenario constrains current models of Solar System formation, as well as the intricate interactions between different constituents of carbonaceous chondrites and their incorporation into planetesimals. Furthermore, our results could provide valuable benchmarks for future laboratory experiments to elucidate how different materials can stick or fragment during collisions in protoplanetary disks.


Figure 1: Gap-opening by Jupiter at different stages. Blue and black dots indicate matrix-like material and refractory inclusions or chondrules, respectively. Left: at the early stages of the gap-opening, small fragments of matrix-like material leak through the gap, enriching the abundances of refractory inclusions and chondrules in the outer regions of the gap. Right: at later stages, gas density decreases, and matrix loss is reduced. Consequently, the abundance of matrix-like material increases outside the gap.



How to cite: Gurrutxaga, N., Drazkowska, J., and Kleine, T.: Modeling the formation of carbonaceous chondrite parent bodies, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-900, https://doi.org/10.5194/epsc2024-900, 2024.

On-site presentation
Sarah Anderson, Pierre Vernazza, and Miroslav Brož


To date, the vast majority of meteorites (≥99%) originate from asteroids in orbits between Mars and Jupiter, yet reaching a consensus on how their diverse chemical, compositional, and isotopic characteristics align with an in-situ formation model within the asteroid belt remains elusive. Recent dynamical models, leveraging measurements from carbonaceous chondrites (CCs), suggest that meteorites may originate from varied heliocentric distances, spanning from the terrestrial planet formation zone to the Kuiper Belt [1, 2, 3]. This broad range is evident in the distribution dichotomies among CCs, especially between CM chondrites (Ch, Cgh-types) and CI chondrites (B, C, Cb, and Cg-types), which collectively account for over 50% of the asteroid belt's mass, excluding Ceres  [4, 5, 6]. These groups show distinctly different spatial distributions (Fig. 1): CM-like bodies display a Gaussian profile, whereas CI-like bodies show an asymmetric distribution, similar to comet-like P-type asteroids [7]. Our study aims to explore the formation and migration history of these asteroid types within the context of giant planet evolution and solar system dynamics to determine whether CM and CI chondrites originated from different locations or at different times.

We use an orbital model initially developed by Ronnet et al. (2018) [8] to investigate the injection of planetesimals into the asteroid belt following giant planet growth in the protoplanetary disk (PSD). We conduct simulations using REBOUND, consisting of 20,000 test particles each, representing 100-km-sized planetesimals. Our five-planet model, inspired by the works of Nesvorný et al. (2015) [9] and Dienno et al. (2017) [10], features Jupiter, Saturn, an additional ice giant (commonly ejected from the solar system), Uranus, and Neptune. Initially, planets are located on low-eccentricity orbits, with Jupiter at 5.4 au and Saturn at the edge of its gap, at 7.3 au. We choose to neglect the influence of the telluric planets, which, having relatively small orbits, require more computation time. We place Neptune in two different configurations: a 'tight' configuration at 16.2 au, in a 3:2, 3:2, 3:2, 3:2 resonance chain, and a 'wide' configuration at 20.3 au, in a 3:2, 3:2, 2:1, 3:2 resonance chain. The test particles' semi-major axes are initialized uniformly between 7 au and 1 au beyond the orbit of Neptune. We examine the effects of gas profile (Σg), planetary growth timescale (τgrowth), and the viscosity parameter (α) on the distribution of planetesimals implanted in the asteroid belt. Notably, we investigate three different gas profiles: the traditional canonical model with a radial dependency of Σg ∝ r−0.5 [11], the Desch et al. 2018 model [12], and the Raymond & Izidoro 2017 model [3].

This study's findings aim to contribute significantly to our understanding of the dynamic processes that shaped the early solar system and the specific pathways that led to the observed dichotomy—or trichotomy—in carbonaceous chondrite composition. By comparing the outcomes of our simulations with existing data, we anticipate providing new insights into the ongoing debate over the formational contexts of these asteroids, thereby enhancing the broader astrophysical models concerning planetary formation and migration.

Figure 1: Distinct spectral classifications (CM, CI/IDP, S) reveal systematic differences in the distributions of main-belt asteroids with D>100 km.

[1] A. Morbidelli et al., Chaotic capture of Jupiter’s Trojan asteroids in the early Solar System, 435.7041 (May 2005), pp. 462–465.
[2] Kevin J. Walsh et al., A low mass for Mars from Jupiter’s early gas-driven migration, 475.7355 (July 2011), pp. 206–209.
[3] Sean N. Raymond and Andre Izidoro, Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn’s rapid gas accretion, 297 (Nov. 2017), pp. 134–148.
[4] Timo Hopp et al., Ryugu’s nucleosynthetic heritage from the outskirts of the Solar System, Science Advances 8.46 (2022), eadd8141.
[5] Toru Yada et al., Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu, Nature Astronomy 6 (Dec. 2021), pp. 214–220.
[6] Tetsuya Yokoyama et al., Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites, Science 379.6634 (2023), eabn7850.
[7] P. Vernazza et al., VLT/SPHERE imaging survey of the largest main belt asteroids: Final results and synthesis, 654, A56 (Oct. 2021), A56.
[8] T. Ronnet et al., Saturn’s Formation and Early Evolution at the Origin of Jupiter’s Massive Moons, 155.5, 224 (May 2018), p. 224.
[9] David Nesvorný, Evidence for slow migration of Neptune from the inclination distribution of Kuiper Belt objects, The Astronomical Journal 150.3 (Aug. 2015), p. 73.
[10] Rogerio Deienno et al., Constraining the Giant Planets’ Initial Configuration from Their Evolution: Implications for the Timing of the Planetary Instability, 153.4, 153 (Apr. 2017), p. 153.
[11] P. Cresswell and R. P. Nelson, Three-dimensional simulations of multiple protoplanets embedded in a protostellar disc, 482.2 (May 2008), pp. 677–690.
[12] Steven J. Desch, Anusha Kalyaan, and Conel M. O’D. Alexander, The Effect of Jupiter’s Formation on the Distribution of Refractory Elements and Inclusions in Meteorites, The Astrophysical Journal Supplement Series 238.1 (Sept. 2018), p. 11.

How to cite: Anderson, S., Vernazza, P., and Brož, M.: Distinct origins for CM and CI-like bodies: Saturn formation region versus trans-Neptunian disk, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-63, https://doi.org/10.5194/epsc2024-63, 2024.

On-site presentation
Raphael Marschall and Alessandro Morbidelli

There is a general consensus that cometesimals formed in an original reservoir, the primordial Kuiper-belt (PKB), between 20-40 au from the Sun (e.g., review by Nesvorny 2018). From there, they were scattered into the current trans-Neptunian region. In particular, the so-called scattered disk acts as the source reservoir for Jupiter family comets, JFCs (e.g., Duncan & Levison 1997). Yet, the current formation region is primarily constrained by the dynamics that lead to the current day structure of the Kuiper-belt.

Here, we discuss independent constraints coming from noble gas abundances. We combine the data from the two instruments ROSINA (Balsiger et al. 2007; Rubin et al. 2018) and COSIMA (Kissel et al. 2007; Bardyn et al. 2017) onboard ESA's Rosetta mission to derive the bulk elemental composition of comet 67P. These measurements show that Krypton and Xenon are only slightly depleted compared to the solar composition, while Argon is strongly depleted. For comparison, e.g., CI chondrites are heavily depleted in these three noble gases. This suggests that comets formed further out in the protoplanetary disk at a distinctly different distance than the parent bodies of CI meteorites. It also suggests that comets formed between the Xenon and Argon condensation lines. The Krypton line, which lies between the Xenon and Argon lines, is at about 25 au for a passive disk. We will show our latest protoplanetary disk models and their implications on where the respective temperatures occur in the disk in more detail.

How to cite: Marschall, R. and Morbidelli, A.: Constraining the formation region of comets., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-492, https://doi.org/10.5194/epsc2024-492, 2024.

On-site presentation
Eleonora Bianchi

How does the chemical complexity evolve during the process leading to the formation of a Sun and its planetary system? Is the chemical richness of a Solar-like planetary system at least partially inherited from the earliest stages, or is there a complete chemical reset? A powerful approach to start addressing these questions is by comparing the observed astrochemical content in young protostellar disks with that found in comets—i.e., with the most pristine known material from which our Solar System formed.

The protostellar disk phase is characterized by the blooming of molecular complexity: when the inner regions (~100 au) are heated to temperatures greater than 100 K, dust mantle products thermally sublimate and enrich the chemical composition of the gas (the so-called hot-corino phase).  Additionally, dramatic changes in molecular abundances are expected due to warm gas chemistry. Several lines of evidence suggest that planets could begin forming very early when the protostellar disk is still deeply embedded in a prominent envelope (less than 1 Myr). Consequently, young protostellar disks in the Class 0/I stage serve as the perfect laboratory to study the initial conditions and chemical content of planetesimal formation.

I will present abundance ratios of interstellar complex organic molecules measured in young Class 0/I protostellar disks and compare them with those measured in the 67P/Churyumov–Gerasimenko and other comets. I will emphasize possible evolutionary trends to investigate the inheritance scenario.

How to cite: Bianchi, E.: Tracing our chemical origins: interstellar complex organic molecules from protostellar disks to Solar System comets, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-985, https://doi.org/10.5194/epsc2024-985, 2024.

Virtual presentation
Sebastian Marino

ExoKuiper belts are a common component of planetary systems that occupy their cold outer regions and whose dust is readily detectable in around 20% of stars. This makes these belts ideal objects to probe those outer regions where planet surveys have struggled to detect all but the most massive exoplanets. The dust in exoKuiper belts is not simply a leftover from protoplanetary discs, it rather is a product of collisions of much larger planetesimals. These belts thus offer a unique window to study the formation and evolution of planetesimal discs as the distribution of dust encodes the planetesimal formation history of these systems.

Over the last 10 years, ALMA dust observations have transformed our understanding of exoKuiper belts by constraining their morphology. This has revealed a great diversity in terms of belt radii and widths. The ongoing ALMA large program ARKS is constraining the detailed structure of these discs for the first time.  In this talk, I will give an overview of the results of this program, with a specific emphasis on the radial structure of these discs. Preliminary results show a wide diversity of substructures, some of which resemble the multi-ring structures in protoplanetary discs. This comparison between the substructures in exoKuiper belts with those in protoplanetary discs can tell us where planetesimal formation is most efficient in protoplanetary discs. 

How to cite: Marino, S.: What does the structure of exoKuiper belts tell us about planetesimal formation?, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-107, https://doi.org/10.5194/epsc2024-107, 2024.

Virtual presentation
Boncho Bonev, Karen Willacy, Erika L. Gibb, Neal Turner, Neil Dello Russo, Michael A. DiSanti, Ronald J. Vervack, Jr., Younas Khan, Nathan X. Roth, Sara Faggi, Adam J. McKay, Mohammad Saki, Hideyo Kawakita, Geronimo L. Villanueva, and Chemeda T. Ejeta

Jupiter-family comets (JFCs) are dynamically-sourced in the scattered Kuiper disk, and are generally less productive than Oort Cloud comets (OCCs). For this reason, JFCs have been underrepresented in ground-based observations of volatiles, such as C2H2, C2H6, CH3OH, HCN, H2O, NH3, H2CO, and especially CO and CH4, for which large Doppler shifts are needed to offset cometary lines from their telluric counterpart absorptions.

The period since 2017 has encompassed some of the best apparitions of JFCs in modern history. These have benefitted from the availability of significantly improved instrumentation for near-IR spectroscopy, and have also coincided with increased synergy between studies of cometary volatiles and model simulations of protoplanetary disk (PPD) chemistry. This presentation will connect findings stemming from near-IR observations of JFCs and OCCs with predictions of PPD midplane ices produced by chemical models for the early solar nebula [Willacy et al. 2022; Astrophysical Journal, 931:164]. Open questions will be discussed in the context of better disentangling natal heritage in cometary volatiles from signatures of post-formative processing, as is needed to understand the comet – early solar system link.

Acknowledgments: Team members gratefully acknowledge support from the following US funding programs: NSF/AAG, NASA/SSO, and NASA/EW. This work benefited from discussions at the International Space Science Institute in Bern during meetings of International Team 361, “From Qualitative to Quantitative: Exploring the Early Solar System by Connecting Comet Composition and Protoplanetary Disk Models.”

How to cite: Bonev, B., Willacy, K., Gibb, E. L., Turner, N., Dello Russo, N., DiSanti, M. A., Vervack, Jr., R. J., Khan, Y., Roth, N. X., Faggi, S., McKay, A. J., Saki, M., Kawakita, H., Villanueva, G. L., and Ejeta, C. T.: Volatiles in Jupiter-family Comets: Synergy Between Infrared Observations and Protoplanetary Disk Chemistry Models, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1297, https://doi.org/10.5194/epsc2024-1297, 2024.

On-site presentation
Nicolas Kaufmann, Yann Alibert, Octavio Guilera, and Irina Sebastian

One of the most promising formation pathways for planetesimals is the concentration of dust via Streaming instability (SI) and the subsequent gravitational collapse into planetesimals. Due to the enhanced dust-to-gas ratio required to trigger the formation via gravitational collapse, the localized formation of a narrow ring of planetesimals is considered in multiple previous studies [3,4]. The subsequent growth of these planetesimals is dominated by mutual collisions up to sizes where they accrete pebbles efficiently. As the timing of core assembly is crucial to the formation of giant planets, understanding the growth of the planetesimals is vital for our understanding of planet formation.


To investigate this scenario, we simulate the formation of the seed of pebble accretion from a filament of planetesimals formed via gravitational collapse. To consistently simulate this early stage of planet formation, we utilize an adapted version of the “Bern model” [1,2]. We track the growth of the largest planetesimal whose initial size is dictated by the initial mass function from Streaming instability simulations [5] from a filament of planetesimals described by a 1D Eulerian disk. Our model newly includes the consideration of multiple important effects that have been neglected or simplified in previous studies: Namely, the viscous spreading of the planetesimals, fragmentation due to the mutual collisions, pebble accretion onto the planetesimals and an improved calculation of the random velocities of the planetesimals which is vital for this stage of planet formation.


In Figure 1. We can see the mass of the largest body in the filament at different times for different locations of the initial planetesimal ring (solid lines). The red dashed line refers to the onset mass of pebble accretion and the blue dashed line to the transition mass [6] above which pebble accretion becomes efficient. The black lines refer to the initial mass of the largest planetesimal (dashed) and the total mass of the ring (dotted). As we can see the growth of the largest body is strongly delayed in the outer disk making it challenging to form the seed of pebble accretion in time to form giant planets. Note that in these simulations we neglected the accretion of pebbles onto the planetesimals and the fragmentation of the planetesimals and are therefore a very conservative estimate for the mass growth of the largest planetesimal.


In conclusion, the formation of a body large enough to accrete pebbles efficiently from a Ring of locally formed planetesimals proves challenging at large separations and is very sensitive to multiple parameters like the stellar mass and the diffusive widening of the filament due to mutual gravitational stirring.



[1] Emsenhuber, A., Mordasini, C., Burn, R., et al. 2021, A&A, 656, A69

[2] Kaufmann, N. & Alibert, Y. 2023, A&A, 676, A46

[3] Lorek, S. & Johansen, A. 2022, A&A, 666, A108

[4] Liu, B., Ormel, C. W., & Johansen, A. 2019, A& A, 624, A114

[5] Schäfer, U., Yang, C.-C., & Johansen, A. 2017, A&A, 59, A69

[6] Ormel, C. W. 2017, in Astrophysics and Space Science Library, ed. M. Pessah & O. Gressel, Vol. 445, 197

How to cite: Kaufmann, N., Alibert, Y., Guilera, O., and Sebastian, I.: Bridging the Gap, From Planetesimals Formation to the Onset of Pebble Accretion: Investigating the Early Growth of Locally Formed Planetesimals, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-997, https://doi.org/10.5194/epsc2024-997, 2024.

Coffee break
Chairperson: Raphael Marschall
On-site presentation
Francesco Zagaria

Over the last decade, the Atacama Large Millimeter/submillimeter Array (ALMA) made it possible to observe protoplanetary discs, the birth sites of planets, at unprecedented angular resolution and sensitivity, revolutionising our understanding of planet formation. When observed at high-enough angular resolution, protoplanetary discs show sequences of axisymmetric dark and bright substructures, colloquially referred to as “gaps and rings”. The origin of such substructures and the role that they play in the planet formation process are, however, still debated. Substructures are considered to be either the signposts of ongoing interactions between (proto-)planets and their hosting discs, or the ideal location for the formation of new planetary bodies. The best way to solve this “chicken and the egg” problem is characterising the physical properties of these gaps and rings. In this talk, I will first discuss recent attempts to observationally infer the size, density, and temperature of dust in these rings, relying on collecting and modelling multi-frequency, i.e. (sub-)mm to cm, continuum observations in a handful of well studied systems. In particular, I will focus on CI Tau, the only T Tauri star where a candidate hot Jupiter was detected using radial velocity techniques. My high-angular resolution and sensitivity ALMA and VLA continuum observations of this source, reveal that the dust density and size locally increase at the position of the bright rings, suggesting that dust trapping is taking place. I will also show how CI Tau's unique spectral energy distribution allows putting unprecedented constraints on dust composition in this system. Finally, I will introduce a new technique that combines these dust properties with gas kinematics to understand if bright rings might be prone to the formation of planetesimals under streaming instability (SI). In the case of HD 163296, the only source where dust properties and gas kinematics have been well constrained so far, my method reveals that the outermost (100 au) ring shows favourable conditions to trigger the SI.

How to cite: Zagaria, F.: From dust to planets: the ALMA and VLA view of planet formation, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-665, https://doi.org/10.5194/epsc2024-665, 2024.

On-site presentation
Gwendolyn Meeus

Exoplanets are often found around Main Sequence stars, but around pre-Main Sequence stars (PMS) it is much harder to find them, and only one confirmed case exists so far. Therefore, it is common to look for indirect signatures of planets in the discs around PMS stars. In this talk, I will discuss detections of variable absorption features of metals in the UV spectra of intermediate-mass PMS stars (the so-called Herbig stars), attributed to (in)falling evaporative bodies (FEBs). These features appear to only be present in flat discs (Meeus group II) , and not in the more flared, gapped discs (Meeus group I) that often are thought to host giant planets, causing large gaps. The absence of signatures of FEBs in the UV spectra could be due to a filtration process at the edge of the gap, halting dust and larger bodies that contain material  with high evaporation temperatures (Si, Fe, Mg,..), while the material with low evaporation temperatures (C,N,O) can flow freely as gas towards the star, where it will be accreted. Such a selective accretion process can cause an underabundance of metals in the photosphere of non-convective stars, what can be verified through spectroscopic metallicity studies, and has indeed already been found in several group I discs around Herbig stars (e.g. Kama et al. 2015, A&A 582, L10; Guzman et al. 2023, A&A  671, 140). 

How to cite: Meeus, G.: Falling Evaporating Bodies in young intermediate mass stars: linked with disc structure?, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1180, https://doi.org/10.5194/epsc2024-1180, 2024.

On-site presentation
Tommy Chi Ho Lau, Til Birnstiel, Joanna Dra̧żkowska, and Sebastian Stammler

Planet formation models are necessary to understand the origins of diverse planetary systems. Circumstellar disc substructures have been proposed as preferred locations of planet formation but a complete formation scenario has not been covered by a single model so far.We aim to study the formation of giant planets facilitated by disc substructure and starting with sub-micron-sized dust. We connect dust coagulation and drift, planetesimal formation, N-body gravity, pebble accretion, planet migration, planetary gas accretion and gap opening in one consistent modelling framework. We find rapid formation of multiple gas giants from the initial disc substructure. The migration trap near the substructure allows the formation of cold gas giants. A new pressure maximum is created at the outer edge of the planetary gap, which triggers the next generation of planet formation resulting in a compact chain of giant planets. A high planet formation efficiency is achieved as the first gas giants are effective in preventing dust from drifting further inwards, which preserves materials for planet formation. Sequential planet formation is a promising framework to explain the formation of chains of gas and ice giants.

How to cite: Lau, T. C. H., Birnstiel, T., Dra̧żkowska, J., and Stammler, S.: Sequential giant planet formation initiated by disc substructure, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-309, https://doi.org/10.5194/epsc2024-309, 2024.

On-site presentation
Ana Luiza Silva, Gavin Coleman, Richard Nelson, Othon Winter, and Rafael Sfair

Context. Since the detection of the first known transiting circumbinary planet (CBP), Kepler-16b,
by the Kepler mission, a total pf 14 CBPs have been detected, raising questions about their formation
and dynamical evolution. The current picture of how a planet forms involves a multistage process
consisting of planetary embryo formation, the accretion of pebbles and planetesimals, and finally gas
Numerous previous works have investigated the processes involved in planet formation and one way
of performing this analysis is to use hydrodynamic simulations ([6], [3]). This approach has led to a
deeper understanding of the processes that likely lead to the formation of circumbinary planets such
as the Kepler-16, -34 and -35 systems ([8], [2]).
Pebble accretion has been explored also in the formation of planets around single star systems ([4],
[5]). An important consideration is the ability of a planet to open gaps in the dust and gas in the disc
in the vicinity of the planet, depending on the mass of the planet, as presented in [7], for example.
Aims. In this work, we explore how circumbinary planets undergo pebble accretion while embedded
in circumbinary discs close to the vicinity of the central binary system. To calibrate our simulations,
we compare the evolution and results to similar planets accreting in discs around single stars. We aim
to understand the differences that might arise between both formation scenarios and to understand its
consequences for the growth of the planets and the final masses of circumbinary planets versus planets
around single stars.
Methods. In this work we use a modified version of the FARGO3D ([1]) that treats the dust as a
fluid consisting of particles with a given internal density and a fixed size, and includes pebble accretion
onto the planet.
We simulate pebble accretion onto small planets around single and binary star systems with this
multi-fluid routine, using Kepler-16 as a template. The evolution of a low mass core embedded in a
gas disc with a continuous flux of pebbles passing through the system is carefully analyzed.
Results. Pebble accretion efficiency depends mostly on the size of the dust, dust-to-gas ratio, planet
mass and initial orbital location. In our preliminary runs we have observed the opening of gaps in
the dust disc and in the gas disc while the planet’s mass is increasing due to pebble accretion. In our
ongoing simulations, we are evolving both single star and binary systems with an embedded planet.
In line with previous work, we expect the binary systems to form an eccentric inner cavity in their
cicumbinary discs, and this is expected to influence the orbital evolution of the planet and its efficiency
in accreting pebbles compared to planets orbiting a single star.
Conclusions. This work compares a single star with a binary star system in the context of planet
formation and the results are relevant to understanding the different evolutionary paths the same
initial setup can produce because of the presence of the binary. The pebble accretion efficiency will
define which of the scenarios will grow a more massive core, and this will depend on the initial system
parameters. We expect our results to show that compact circumbinary planets will be more massive
than the ones around the single stars, due to the eccentric disc and planet leading to more efficient
pebble accretion.


[1] Benı́tez-Llambay, P., and Masset, F. S. Fargo3d: A new gpu-oriented mhd code. The
Astrophysical Journal Supplement Series 223 (2016).
[2] Coleman, G. A., Nelson, R. P., and Triaud, A. H. Dusty circumbinary discs: inner cavity
structures and stopping locations of migrating planets. Monthly Notices of the Royal Astronomical
Society 513 (2022).
[3] Kley, W., and Nelson, R. P. Planet-disk interaction and orbital evolution, 2012.
[4] Lambrechts, M., and Johansen, A. Rapid growth of gas-giant cores by pebble accretion.
Astronomy and Astrophysics 544 (2012).
[5] Lambrechts, M., Johansen, A., and Morbidelli, A. Separating gas-giant and ice-giant
planets by halting pebble accretion. Astronomy and Astrophysics 572 (2014).
[6] Nelson, R. P. On the evolution of giant protoplanets forming in circumbinary discs. Monthly
Notices of the Royal Astronomical Society 345 (2003).
[7] Paardekooper, S. J., and Mellema, G. Planets opening dust gaps in gas disks. Astronomy
and Astrophysics 425 (2004).
[8] Pierens, A., and Nelson, R. P. Migration and gas accretion scenarios for the kepler 16, 34,
and 35 circumbinary planets. Astronomy and Astrophysics 556 (2013).

How to cite: Silva, A. L., Coleman, G., Nelson, R., Winter, O., and Sfair, R.: Multi-fluid hydrodynamical simulations of circumbinary planet formation via pebble accretion, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-635, https://doi.org/10.5194/epsc2024-635, 2024.

On-site presentation
Anna Bauernfeind, Remo Burn, Oliver Voelkel, and Hubert Klahr

Planetary population synthesis is a tool to investigate planet formation by using a simplified global end-to-end planet formation model to create artificial planet populations. This makes it possible to statistically compare model predictions with observations, and to better understand the physical mechanisms of planet formation and their interactions. This project uses the Bern population synthesis model for planetary formation but pushes its boundaries to the earlier stage of planetesimal and embryo formation. 

The model combines the two-population model (Birnstiel et al. 2012) for the solid evolution with a pebble-flux regulated planetesimal formation (Lenz et al. 2019), and then grows planetary embryos from the planetesimals (see Voelkel et al. 2021, paper II). This eliminates the strong assumption of where to place initial planetary embryos in planet formation models. 

Further, we use a modern disk model including an MRI-like alpha transition, weak disk winds (Weder et al. 2023), and thermal torques for planetary migration. Parameters like the planetesimal size and planetesimal fragmentation velocity were varied, and the influence of migration and pebble accretion on the planet evolution were also studied. 

We find a significant under-representation of giant planets, especially cold giants, in all our populations. Only by excluding orbital migration, a sufficient number of cold giant planets could form. Reducing the planetesimal fragmentation velocity or increasing the efficiency of pebble-to-planetesimal conversion all strongly reduce the fraction of giants. These results highlight the added complexity of including a self-consistent planetesimal and embryo formation in global planet formation models.

Figures: Mass-distance evolution of the formed planets in two systems of the nominal population. Violet tracks mean the planet formed early, yellow tracks that it formed late. Horizontal lines mean the planet was ejected from the system. Dotted lines mean the planet was destroyed (ejected, accreted by star, collided with another planet)



Emsenhuber, A., Mordasini, C., Burn, R., Alibert, Y., et al. 2021, A&A 656, A69

Lenz, C.T., Klahr, H. & Birnstiel, L. 2019, ApJ 874 A36

Völkel, O., Deienno, R., Kretke, K., & Klahr, H. 2021, A&A 645, A132 

Weder, J., Mordasini, C., Emsenhuber, A. 2023, A&A 674, A165

How to cite: Bauernfeind, A., Burn, R., Voelkel, O., and Klahr, H.: The formation of giant planets in disks with consistent planetesimal and embryo formation, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1141, https://doi.org/10.5194/epsc2024-1141, 2024.

On-site presentation
Tom Benest Couzinou, Alizée Amsler Moulanier, and Olivier Mousis

The outer solar system bodies, including the Galilean moons, are expected to have accreted carbonaceous material during their formation. This carbonaceous material is likely composed of Complex Organic Molecules (COMs), whose formation could have taken place in the protosolar nebula. During their journey through the disk, icy pebbles may have been exposed to different interstellar UV irradiation and temperature conditions, which could have led to the formation of COMs, as experimental studies under similar conditions have demonstrated.

Regarding the formation of the Galilean moons, several scenarios are possible. This study focuses on the formation of the moons in a cold circumplanetary disk, implying that the building blocks originating from the protosolar nebula are not altered by the circumplanetary disk, and their composition is determined solely by the thermodynamic conditions of the protosolar nebula.

The aim of this study is to investigate whether the thermodynamic conditions in the disk were consistent with the formation of COMs in the environment where the Galilean moons formed. To achieve this, the following approach has been taken: 

  •  two-dimensional model has been developed to compute the transport of particles within the protosolar nebula using a Lagrangian scheme. This model deduces the accumulated irradiation dose along the particles' paths.
  • based on experimental data, the model demonstrates that a small fraction of particles consistently transports COMs within the Jupiter region.

By combining theoretical modeling and experimental data, this study aims to shed light on the potential formation and incorporation of COMs into the Galilean moons during the early stages of the solar system's evolution.

How to cite: Benest Couzinou, T., Amsler Moulanier, A., and Mousis, O.: Investigating the Formation of Complex Organic Molecules in the Protosolar Nebula and Their Incorporation into the Galilean Moons, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-216, https://doi.org/10.5194/epsc2024-216, 2024.

On-site presentation
Oliver Schib, Christoph Mordasini, Ravit Helled, and Alexandre Emsenhuber

Disc instability remains the leading formation pathway for some of the observed giant planets. In particular, this model can more naturally explain giant planets at large separation, giant planets around M stars, and very young giant planets. However, there are still many open questions regarding this formation mechanism, and the expected population of planets is currently unknown.
We present the results of a new disc instability population synthesis (DIPSY) that addresses many of these questions and makes predictions about the expected population of planets that can be tested observationally.
Our model describes the formation of a star-and-disc system and its evolution until the disappearance of the disc and beyond. It includes a large number of physical effects: gravitational interaction between forming companions, self-consistent gas-accretion, migration and many more.
We find that, while fragmentation (the formation of bound clumps of gas in the disc, a necessary condition for planet formation in the disc instability model) may only happen in a minority of systems, it typically leads to the formation of at least one companion when it does.
The inferred population of companions spans a large range of masses, from the planetary to the stellar regime.
We present and discuss this population, as well as the influence of a number of assumptions.
The figure shows the result of the baseline run: the mass-distance diagram for 100’000 systems after 100 Myr. The final host star mass is given as colour code.

Mass-distance diagram for a population of companions formed through disc instability
The results of the population synthesis will provide hints both for the theoretical study of planet formation (e.g. hydrodynamic simulations) and future observational surveys of companions.
DIPSY contributes to our understanding of planet formation irrespective of the formation model.

How to cite: Schib, O., Mordasini, C., Helled, R., and Emsenhuber, A.: DIPSY: A New Disc Instability Population Synthesis, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-901, https://doi.org/10.5194/epsc2024-901, 2024.


Posters: Fri, 13 Sep, 10:30–12:00

Display time: Fri, 13 Sep 08:30–Fri, 13 Sep 19:00
Chairpersons: Raphael Marschall, Joanna Drazkowska, Manuela Lippi
On-site presentation
Kertu Metsoja, Mihkel Kama, Colin Folsom, and Anna Aret

The chemical composition of two binary stars, HD 135344A and HD 135344B, is compared, from which conclusions can be drawn about the protoplanetary disk around the star HD 135344B. Since binary stars are form from the same gas and dust cloud, their chemical composition is thought to be similar. To study the protoplanetary disk around the secondary star we have to characterize the host star and the primary star for a comparative analysis. The HD 135344B disk is one of the least known transition disks, which has asymmetrical properties in scattered light and heat radiation. Photometric images of near-infrared scattered light shows two big spiral arms and an internal dust-free cavity.

Spectral observations are used to determine the physical parameters and chemical composition of stars, which are matched to synthetic model spectra. The synthetic or model spectrum is found by the Zeeman spectrum sythesis code, which is written in the programming language Fortran. 

In our presentation, we will present our conclusions regarding the chemical composition of the HD 135344B disk based on the comparative analysis of the binary system’s chemical composition.

How to cite: Metsoja, K., Kama, M., Folsom, C., and Aret, A.: Comparative analysis of a binary system HD 135344 with a protoplanetary disk, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-953, https://doi.org/10.5194/epsc2024-953, 2024.

On-site presentation
Stanley Baronett, Yan-Fei Jiang, Philip Armitage, and Zhaohuan Zhu

In protoplanetary disks of gas and dust, sub-micron interstellar grains must grow at least 13 orders of magnitude in size to become terrestrial planets. The frequency-dependent opacities of these silicate grains to pre-main-sequence stellar radiation affect the thermodynamic structure of the disk, which itself influences the various stages of planet formation and migration. With a reduced overall opacity skewed toward shorter wavelengths, the tenuous disk atmosphere heats up as dust preferentially absorbs ultraviolet rays from the young star, while settled grains make the disk midplane optically thick and cooler. Conventional disk and planet formation models, however, use simplified assumptions about the thermodynamic structure, including vertically isothermal temperature profiles, Planck- or Rosseland-mean dust opacities, and flux-limited-diffusion approximations to radiation transport valid only in optically thick regions. Thus, further development of more detailed and self-consistent disk profiles using multifrequency radiation hydrodynamics is warranted. We use the Athena++ finite-volume hydrodynamics code, extended with multigroup radiation transport, to develop and analyze new stellar-irradiated disk models that include the frequency-dependent opacities of silicate dust grains. As the radiation module neither assumes a diffusion-dominated limit nor treats the radiation field as another fluid, our models can better capture the full dynamic range in disk optical depths.

How to cite: Baronett, S., Jiang, Y.-F., Armitage, P., and Zhu, Z.: Radiation hydrodynamics of protoplanetary disks with frequency-dependent dust opacities, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1204, https://doi.org/10.5194/epsc2024-1204, 2024.

Virtual presentation
Daniela Ascenzi, Luca Mancini, Emília V. Ferreira de Aragão, Fernando Pirani, Marzio Rosi, Noelia Faginas-Lago, Vincent Richardson, Linda Podio, Manuela Lippi, and Claudio Codella

Methyl cyanide (a.k.a. acetonitrile) is a molecule of great astrochemical interest as it is one of the simplest interstellar complex organic molecules (iCOMs) routinely detected in young solar analogues. It has been observed in Class 0 and I hot-corinos (e.g. Taquet et al. 2015, Yang et al. 2021, Bianchi et al. 2022, Ceccarelli et al. 2024), in shocked regions (e.g., Codella et al. 2009), as well as in planet-forming disks (Öberg et al. 2015, Bergner et al. 2018, Loomis et al. 2018, 2020, Ilee et al. 2021). Moreover, CH3CN has been detected in comets, including towards 67/P Churyumov-Gerasimenko in the context of the ESA-Rosetta mission (Le Roy et al. 2015; Altwegg et al. 2019). Nitriles have a strong prebiotic relevance, as they act as intermediates in the formation of biomolecules, by reacting with water and participating in multi-step synthesis of amino acids/RNA precursors (e.g. Sutherland 2017). Hence the presence of nitriles and water in comets, with CH3CN ranging from ~0.008 to 0.054% with respect to water (Biver & Bockelée-Morvan 2019), is particularly interesting, and makes CH3CN a key species to explore the "chemical" connections between disks and comets. However, for such comparison to be meaningful, reaction rates and branching fractions for CH3CN formation and destruction pathways should be updated.

The network of gas-phase formation routes of CH3CN has been revised and extended recently (Giani et al. 2024), and here we focus on its destruction routes by collisions with energetic ions H+, H3+, HCO+ and He+. While the reactions of H3+ and HCO+ lead to non-dissociative proton transfer (see experiments cited in KIDA and UMIST databases) giving CH3CNH+ (from which methyl cyanide can be regenerated by recombination with electrons or proton transfer to NH3), reactions with H+ and He+ are mostly destructive, due to the large exothermicity of the charge exchange process, equal to 12.39 eV in the He+ case. Therefore, collisions with He+ are an important pathway for the decomposition of iCOMs, as demonstrated previously for CH3OCH3, HCOOCH3 and CH3OH (Cernuto et al. 2017, Cernuto et al. 2018, Ascenzi et al 2019, Richardson et al. 2022). For CH3CN, while the reaction with H+ has been experimentally studied (Smith et al. 1992, see the KIDA and UMIST databases), no previous experimental or theoretical studies have been carried out for He+, and the rates reported in the astrochemical databases refer to expectations from capture theories.

By applying a combined experimental and theoretical approach, we have developed the Potential Energy Surface for He+ plus CH3CN (L. Mancini et al. 2024) and we have used it to model the dynamics of the charge exchange process, by determining cross sections and branching ratios in a wide range of collision energies, from which rate constants at varying temperatures can be obtained. The electron capture is expected to occur from an inner valence orbital of CH3CN, leaving the radical cation in a highly excited electronic state leading to complete fragmentation. The main detected ionic fragments are HC2N+/C2NH+, CH2+ and HCNH+, quite different from those proposed in KIDA/UMIST databases (CH3+ and CN+), and the rate constant at T=10 K is 4.6x10-9 cm3molec-1s-1, to be compared with values of 4.5x10-8 and 1.3x10-8 cm3molec-1s-1 from KIDA and UMIST databases, respectively.

Previous astrochemical models suggested that CH3CN in disks is mostly formed on grains, because gas-phase chemistry cannot account for the large observed abundances (Öberg et al. 2015, Loomis et al. 2018). These studies compared the abundance ratios of CH3CN with smaller N-bearing compounds (e.g. HCN, HC3N) in disks and in comets to test the inheritance of disk material into the forming planets and small bodies. Our experiments, however, indicate that the rate coefficient for the destruction of CH3CN through collisions with He+ might be almost one order of magnitude lower than what previously reported. Combined with the revised chemical network for formation of CH3CN (Giani et al. 2024), this may suggest that CH3CN in disks is mostly a gas-phase product. The formation of abundant CH3CN in gas-phase would explain why this molecule is routinely detected in planet-forming disks out to large radii (a few hundred of au), in contrast with CH3OH, which is only formed on grains, hence only detected where grains are sublimated, i.e. in the inner disk region. Our findings are thus expected to have important implications on the origin of methyl cyanide in planet-forming disks, as well as on the comparison of the abundance ratios of N-bearing molecules with cometary abundance ratios.


Altwegg K., Balsiger H. et al. Ann. Rev. A&A 57, 113 (2019)

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Bianchi E., et al. A&A, 662, A103 (2022)

Biver N. & Bockelée-Morvan D. ACS Earth Space Chem. 3, 1550–1555 (2019)

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Codella C., et al. A&A 507, L25 (2009)

Giani L., Ceccarelli C. et al. MNRAS 526, 4535–4556 (2023)

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How to cite: Ascenzi, D., Mancini, L., Ferreira de Aragão, E. V., Pirani, F., Rosi, M., Faginas-Lago, N., Richardson, V., Podio, L., Lippi, M., and Codella, C.: Destruction rates of interstellar methyl cyanide (CH3CN) by collisions with He+ ions, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-370, https://doi.org/10.5194/epsc2024-370, 2024.

On-site presentation
The compaction of highly porous dust agglomerates by a gas-velocity gradient and its application to dust growth in turbulent protoplanetary disks
Rainer Schräpler, Jürgen Blum, Daniyar Balapanov, and Andrei Vedernikov
On-site presentation
Nico Wenders, Kolja Joeris, and Jens Teiser

3D Structure and Stability of Particle Clusters close to the Bouncing Barrier – New Experiments


Collisions of particle clusters in the protoplanetary disk are a key process in the matter of planet formation and therefore formation of solar systems. [1] It is generally accepted that the early phases of planet formation are governed by such collisions.  Collisions can result in different outcomes, such as growth, fragmentation, or restructuring of the cluster. Disk models cannot resolve the detailed physical processes involved, so laboratory experiment help to understand this phase of planet formation. Growth by collision is stalled once a critical aggregate size (Stokes number ≈ 1) is reached, as particles bounce off each other instead of sticking or transferring mass. This critical size range is referred to as the bouncing barrier.

Recent experiments showed that collisional charging is a key process to allow growth beyond the growth barrier. [2] Collisions among particles lead to charge separation resulting in a broad charge distribution within the ensemble, changing the collision dynamics and the resulting structure of growing agglomerates.

Which collision outcome occurs depends on numerous properties of the participating agglomerates. The structure of these clusters is an important aspect in determining how stable the cluster is. In experiments with only one camera perspective much of the structural information gets lost. Due to the projection of a three-dimensional object on the two-dimensional plane depth information is not easily accessible. Using stereo vision, one can calculate the position of particles a cluster in three-dimensional space and further get a more precise description of the clusters before and after the collision to get an in depth understanding of cluster stability. We present novel experiments on the stability of growing clusters and their three-dimensional structure.

To analyze the stability of clusters the experiments are executed in low gravity at the Gravitower Bremen, providing around 2 s of microgravity. Additionally, the experiments are performed under vacuum to exclude the influence of gas drag. The main part of the experiment is a test cell (free volume of 5 cm x 5 cm x 5 cm) with a smaller particle compartment at the bottom. The test cell is agitated in vertical direction, inducing particle-particle collisions while the experiment is still on ground, leading to the formation of clusters of charged particles (either basalt or glass particles).

In microgravity, clusters and single particles are ejected into the free volume by shaking the chamber. Inside the chamber the cluster interacts with the granular gas, which results in abrasion of the cluster surface due to ongoing collisions with small particles. When the cluster hits the wall, the cluster can shrink even further or may be fragmented in smaller clusters and single particles. Therefore, these experiments enhance our understanding of the cluster stability while interacting with a granular gas and when colliding with more solid objects. The experiments are observed with a high temporal resolution and stereo vision. The stereo vision is obtained with a pair of mirrors generating two different images onto different sections of the sensor. Together with an exact calibration of the optical system, this enables a detailed 3D reconstruction of the agglomerates. Therefore, these experiments help to correlate the 3D structure of clusters with the collisional dynamics.


[1] Wurm, Gerhard, and Jens Teiser. "Understanding planet formation using microgravity experiments." Nature Reviews Physics 3.6 (2021): 405-421.

[2] Steinpilz, Tobias, et al. "Electrical charging overcomes the bouncing barrier in planet formation." Nature Physics 16.2 (2020): 225-229

How to cite: Wenders, N., Joeris, K., and Teiser, J.: 3D Structure and Stability of Particle Clusters close to the Bouncing Barrier – New Experiments, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-582, https://doi.org/10.5194/epsc2024-582, 2024.

On-site presentation
Jakob Penner, Jens Teiser, Kolja Joeris, Florence Chioma Onyeagusi, Jonathan Kollmer, and Gerhard Wurm

We conducted experiments with ensembles of colliding sub-millimeter basalt particles under prolonged microgravity conditions on a suborbital flight. In these experiments, the sample motion was excited at different levels. Initial shaking of the particles simulates a classical phase of bouncing in early planet formation. During these collisions, the particles charge, as was measured by applying an electric field. Further moderate shaking then leads to the formation of compact clusters of the charged beads, up to several centimeters in size. These clusters grow by individual impacts up to a velocity threshold of about a meter per second. Beyond that velocity, clusters are eroded. We therefore find a shift in barriers from a bouncing particle at millimeters per second to an eroding cluster at meters per second, going along with a shift in particle size from sub-millimeter up to several centimeters. This allows growth well into a size regime that might make clusters prone to hydrodynamic instabilities and subsequent planetesimal formation.

How to cite: Penner, J., Teiser, J., Joeris, K., Onyeagusi, F. C., Kollmer, J., and Wurm, G.: Growing Super Large Sub-Decimeter Pebbles in Protoplanetary Disks: An Erosion Limit for Electrostatic Clustering from Suborbital Experiments, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-911, https://doi.org/10.5194/epsc2024-911, 2024.

On-site presentation
Thomas Collin-Dufresne, Emmanuel Di Folco, and Arnaud Pierens

I] Context

Structures and asymmetries detected in protoplanetary disks offer an exciting means to characterize the orbital and physical properties of embedded proto-planets, which are suspected to sculpt some of the observed features. A dozen of young disks have been reported to harbor crescent-shaped dust rings at millimeter wavelengths, with compact or more extended brightness features which could be interpreted as dust traps within vortex structures. 

Among these remarkable systems, AB Aurigae is one of very few nearby, young stars, where disk asymmetries and compelling evidence of protoplanets have been concurrently found. This includes the presence of two prominent spiral arms seen in emission from the gas and small dust grains revealed by ALMA and SPHERE within the broad 120au cavity (Tang+2017, Fig.1). In addition, bright spots spread between 30au and 100au were reported with VLT/SPHERE and Subaru/CHARIS, which are debated  sites of giant planet formation (Boccaletti+2020, Currie+2022, Zhou+2023, Fig.2). Beyond the cavity, a broad dust ring displays a large asymmetric brightness that was interpreted as a possible decaying vortex (Fuente+2017). Confirming the planetary nature of the suspected candidates is however a challenging task, and we propose to investigate the putative planet characteristics through the modeling of planet-induced structures in the disk.

Fig 1: radio-millimetric ALMA observation of the asymmetric dust ring (red) and the CO gas spirals (blue) of the circumstellar disk around AB Aurigae


Fig 2: SCExAO/CHARIS image combined with ALMA submillimetre imaging

II] Methods and Setup

We focus here on the large scale crescent shape of the dust continuum emission in the outer ring. We revisit the hypothesis of the existence of a vortex generated by a massive planet orbiting in the cavity, and we further explore how the dust distribution can inform us on the characteristics of the assumed, embedded planet(s).

For this purpose, we have performed a large set of 2D hydrodynamical simulations with the FARGO-3D code in multi-fluid mode. We used a gaseous fluid with a low viscosity  (alpha=1e-4), interacting with a 0.1mm grain-fluid. We introduced a single planet of variable mass within an equilibrium disk in the isothermal approximation, and we explored a large range of orbital properties and planetary masses based on the existing observational constraints. Vortex structures are naturally produced when the Rossby-wave instability develops at the edge of the cavity (Fig.3). We selected the simulation runs where planet-disk interactions resulted in rings located at the observed radial distance of the outer ring, and capable of trapping the dust grains in expected azimuthal structures. Based on FARGO3D dust surface density maps, radiative transfer simulations with the RADMC3D code were performed to simulate the ALMA continuum map. We finally compare the azimuthal extent and contrast ratio of the simulated ring to constrain the possible parameter space for the planet’s characteristics. 

III] Results

A large set of planetary configurations appear consistent with the observed morphological characteristics of the dust crescent (radial location, contrast and azimuthal width). We explored for the first time the case of eccentric planets in this system, and we find that the dust continuum maps can still be reproduced with giant planet orbital eccentricities as large as e=0.6. We illustrate the degeneracy in the semi-major axis-eccentricity domain in Fig. 4, where we also report the planetary mass range compatible with the dust ring morphology (from 2 to 15Mjup depending on the orbit properties). This diagram extends the canonical case of a 2Mjup circular planet located at the outer edge of the cavity proposed and studied in Fuente+2017. In this framework, this study suggests that any independent, direct constraint on the planet semi-major axis and eccentricity can thus provide an estimate for the protoplanet dynamical mass, based on the modeling of the planet-induced structures.


Besides, we note that the large azimuthal extent of the grain distribution within the ring (FWHM>90deg) and its low contrast ratio can only be reproduced when the gas vortex has started to dissipate and thus when the trapped grains are released from their initial compact configuration. The grains then concentrate at the outer edge of the cavity, in the pressure gradient maximum, and rapidly form an azimuthally uniform, symmetrical ring (Fig.5). We discuss how the short timescale of the vortex dissipation restricts the likelihood to observe this short transient phase, when the ring’s morphology matches the observed asymmetry. We also discuss alternative scenarios, including the impact of a slow planet growth-phase (following Hammer+2019), to extend the lifetime of the observed dust crescent.

Fig 3 : The presence of the planet creates in the gas fluid an extremum in the Liso function at the edge of the cavity, forming anticyclonic gas vortices that can trap dust. Liso = cs^2 * Sigma_gas / (nabla ^ v_gas). The color gradient represents the density of dust particles (log scale). Contour lines correspond to an incrementation of 1.25e-6 of Liso. The dust is trapped at the extremum of Liso


Fig 4: Evolution of dust FWHM as a function of planet orbital time

Fig 5: simulated image at λ=0.9mm based on the FARGO3D density map at the time of the vortex dissipation (face-on view). The azimuthal extent and the contrast ratio of the mm ring emission can be reproduced with an embedded eccentric planet in the cavity. 

Fig 6: Each circle on the graph represents a simulated planetary system, characterized by its semi-major axis (x-axis), eccentricity (y-axis) and planetary mass (number/circle size). Connected points correspond to simulations with the same semi-major axis-eccentricity couple but different planetary masses. Green points correspond to the cases reproducing the asymmetrical ring around AB Aurigae.

How to cite: Collin-Dufresne, T., Di Folco, E., and Pierens, A.: Planet-disk interactions in the AB Aurigae system: revisiting the hypothetical vortex, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1112, https://doi.org/10.5194/epsc2024-1112, 2024.

On-site presentation
Christian Reinhardt, Ravit Helled, Yoav Matzkevich, Thomas Meier, and Joachim Stadel

Introduction: The formation of giant planets is a fundamental open question in planetary science. According to the disk instability (DI) model, the formation of giant planets starts with the proto-planetary disk becoming locally gravitationally unstable and fragmenting into cold and extended gaseous clumps. These clumps are expected to have masses of a few times the Jovian mass (MJ) and radii of hundreds to thousands of Jupiter radii (RJ) which makes them susceptible to disruption. The clumps then slowly contract over 104 - 106 years (pre-collapse stage) until hydrogen (H) dissociation initiates a rapid dynamic collapse during which they rapidly contract to a few RJ, leading to the formation of protoplanets. One key ingredient of such models are the gravitational interaction of clumps due to collisions. For simplicity, collisions are modeled assuming point mass for the clumps and any collision is assumed to lead to perfect merging between clumps. These assumptions, however, are inappropriate for modeling clump collisions especially during the early stages of gravitational collapse when the clumps are very extended and are only weakly gravitationally bound.

Methods: We perform a large suite of 3D impact simulations between clumps during the pre-collapse stage with the novel Smoothed Particle Hydrodynamics (SPH) code pkdgrav3.  The clumps are assumed to be made of a Hydrogen (H) and Helium (He) mixture in proto-Solar proportions which is modelled using a version of the SCvH EOS (Saumon et al. 1995) that was extended to the low temperatures occurring during the pre-collapse stage. We consider clump masses of 1, 3, 5 and 10 MJ and three different ages which correspond to different evolution time: after the clump becomes gravitationally bound (“young”), at the middle of the pre-collapse phase (“mid”) and before the dynamic collapse occurs (“evolved”). The density and temperature profiles of the clumps are guided by evolution simulations of isolated clumps during the pre-collapse stage (Helled & Bodenheimer, 2010). For each combination of clump mass and age we perform impact simulations at different impact angles and velocities. After each collision we determine the number of the  remaining clumps, their masses and internal structure and classify the collision outcome (e.g., prefect merger, erosion, disruption or hit-and-run).

Results: We find that the outcomes of clump collisions are extremely diverse and range from perfect merging (PM), erosion and disruption to hit-and-run collisions (HRC) (see Figure 1). PM, as assumed in population synthesis models, are very rare, even for the most favorable conditions (i.e., massive, and relatively old and compact clumps). Clump collisions typically lead to mass loss and erosive and disruptive outcomes are very common. Disruption can already occur for impacts with rather low relative velocities of a few km/s due to the shallow gravitational potential of the clumps. Therefore this collision outcome is expected to be common even at large distances from the central star. For large impact angles and velocities, a transition to HRC occurs and both bodies survive the collision, exchanging mass and angular momentum. We also find that impacts can shorten the time to reach  dynamic collapse over a wide range of impact conditions (Figure 2). This increases the survival probability of clumps since during the pre-collapse phase they are most susceptible to disruption. This in turn could have a substantial impact on the inferred population of giant planets in the disk instability model. 

Conclusions: The outcomes of clump collisions are extremely diverse and the assumption of perfect merging often used in population synthesis models is rarely satisfied. Furthermore, collisions can initiate dynamic collapse, hence shortening the pre-collapse stage during which clumps are most likely to be disrupted. Our simulations show that population synthesis models must account for the diverse collision outcomes. In addition, it is clear that collisions between planetary clumps plays a key role in shaping the distribution of frequency, mass and orbital characteristics of planets in the disk instability model. Our study advances  our understanding of planet formation and early evolution in the disk instability model and clearly shows the need to include realistic collisions outcomes in population synthesis models.

Figure 1: The diverse outcomes of collisions between young 3MJ (top) and evolved 10 MJ (bottom) clumps inferred from 3D impact simulations. Perfect merging which is assumed in population synthesis models is very rare and collisions often result in erosion / disruption of the clumps or hit-and-run encounters. Collisions can also accelerate the stage of dynamical collapse, hence shortening the pre-collapse stage during which clumps are most likely to be disrupted.


Figure 2: A head-on collision between evolved 10 and 5 MJ clumps occurring close to the mutual escape velocity. During the impact a compact region is forming behind the shock front in which the density increases by several orders of magnitude. At a later stage the collapsed region pierces through the shock front and regains hydrostatic equilibrium. After the collision 77% of the total colliding mass remains bound.

How to cite: Reinhardt, C., Helled, R., Matzkevich, Y., Meier, T., and Stadel, J.: The Outcome of Collisions between Gaseous Clumps formed by Disk Instability, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-290, https://doi.org/10.5194/epsc2024-290, 2024.

On-site presentation
Antoine Schneeberger and Olivier Mousis

An understanding of the structure of the circumplanetary disk (CPD) that surrounded Jupiter after the gas runaway accretion phase is essential for comprehending the formation of the Galilean system.  Insights from three-dimensional hydrodynamic simulations indicate that the CPD could have been optically thick1 and heated by the hot young Jupiter2,3. Therefore, an analysis of the impact of Jupiter’s radiative heating and subsequent self-shadowing of the CPD on its structure and composition, may provide insights into the formation conditions of the Galilean satellites.

To assess the impact of Jupiter radiative heating and disk self-shadowing, we have developed a two-dimensional quasi-static CPD model and used a grey-atmosphere radiative transfer to determine its thermal structure. In the model, the CPD actively accretes material from the protoplanetary disk, which accretion rate is derived from a Jupiter formation model4,5, that predicts a depletion over a timescale of 100 kyr. The CPD evolution is simulated over a period of 400 kyr.

The model demonstrates that the CPD undergoes a transition from a fully optically thick and hot state, characterized by a maximum midplane temperature above 2000 K, to a fully optically thin and cold state, with a temperature below 400 K, over a timescale of less than 200 kyr. This transition is linked to the rapid depletion of the accretion rate. During this period, shadows are projected on the disk at distances greater than 10 Jupiter radii. Shadows only influence the CPD temperature when heating by accreting material and viscous stress become negligible compared to Jupiter’s radiative heating, after 150 kyr of evolution. Between 150 and 200 kyr of evolution, the shadowed area, centered around 10 Jupiter radii, experiences a temperature drop of approximately 100 K compared to its surroundings. The extent and duration of shadows are significantly influenced by the CPD metallicity. A higher material metallicity results in longer shadow durations and larger shadowed areas.

The shadowed area can act as a cold trap for volatile species, such as NH3, CO2, and H2S, where their ices are trapped closer to the planet compared to their respective iceline position. Depending on the CPD metallicity, cold traps can last between 35 and 120 kyr at distances centered around 10 Jupiter radii. The existence of the shadows may have influenced the composition of the Galilean moons building blocks, potentially shaping their characteristics, providing an observational test to this model.

A significant distinction between our methodology and that of previous studies is the utilisation of an accretion rate derived from a numerical simulation that exhibits a much faster decay than the more conventional 1 to 3 Myr accretion rate depletion timescale.6. To assess the variability of our results with the accretion rate prescription, we performed a simulation with an accretion rate depletion timescale of 1 Myr over 3 Myr. By doing so, we constat that the CPD remained hotter after 3 Myr than the case with rapidly decreasing accretion rate after 200 kyr. Since accretion and viscous heating dominate over the planet's heating, the shadowed areas do not exhibit significant temperature drops. Therefore, the consequences of CPD self-shadowing only exist for a rapidly decreasing accretion rate after Jupiter's formation.



  • 1- Ayliffe, B. A. & Bate, M. R. Circumplanetary disc properties obtained from radiation hydrodynamical simulations of gas accretion by protoplanets. 397, 657–665 (2009).
  • 2- Szulágyi, J. et al. Circumplanetary disc or circumplanetary envelope? Mon. Not. R. Astron. Soc. 460, 2853–2861 (2016).
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  • 4- Mordasini, C., Alibert, Y., Klahr, H. & Henning, T. Characterization of exoplanets from their formation: I. Models of combined planet formation and evolution. A&A 547, A111 (2012).
  • 5- Mordasini, C. Luminosity of young Jupiters revisited: Massive cores make hot planets. A&A 558, A113 (2013).
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How to cite: Schneeberger, A. and Mousis, O.: Impact of Jupiter’s heating and self-shadowing on its Circumplanetary disk structure, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-203, https://doi.org/10.5194/epsc2024-203, 2024.

On-site presentation
Tom Benest Couzinou and Olivier Mousis

The formation mechanisms of the ice giants Uranus and Neptune, as well as the origin of their elemental and isotopic compositions, have been long-standing subjects of debate. Several puzzling observations have challenged our understanding of these planets' formation processes. Spectroscopic observations have revealed that both Uranus and Neptune are highly enriched in carbon and perhaps deficient in nitrogen, an elemental composition that deviates from predictions based on our current understanding of planet formation. Also, the ices from which Uranus and Neptune originally formed might have had deuterium-to-hydrogen (D/H) ratios lower than the predicted cometary value, a characteristic that has not been envisaged in any other planets in our solar system.

Resolving these puzzles is crucial for advancing our understanding of the formation mechanisms and evolutionary processes that shaped these enigmatic ice giants. One key piece of observational data that can shed light on this mystery is the measurement of the D/H ratio in Uranus, provided by the Herschel space telescope. This measurement is vital for understanding the current planetary composition of Uranus.

The aim of this study is to investigate whether the CO/H2O ratio of Uranus, inferred from the D/H measurement, is consistent with the composition in the protosolar nebula during its evolution. To achieve this, the following approach has been employed:

  • Interior Models. Using interior models and assuming a cometary D/H value in the primitive ices of Uranus, the contemporary D/H measurement from Herschel can be related to the bulk CO/H2O ratio of Uranus.
  • Protoplanetary Disk Evolution Model. A protoplanetary disk evolution model that includes solid and gaseous phases, as well as clathrates, has been utilized to simulate the evolution of the CO/H2O ratio in the protosolar nebula over time.
  • Comparison of Ratios. The preliminary results compare the inferred CO/H2O ratio of Uranus with the local CO/H2O ratio in the protosolar nebula at different epochs, providing insights into the local conditions present during the formation of Uranus.

By combining observational data, interior models, and protoplanetary disk simulations, this study aims to shed light on the connection between the composition of Uranus and the conditions in the PSN during the planet's formation process.

How to cite: Benest Couzinou, T. and Mousis, O.: Investigating Uranus' formation through the D/H ratio, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-885, https://doi.org/10.5194/epsc2024-885, 2024.

On-site presentation
Jiahan Shi, Matthias Bartelmann, Hubert Klahr, and Cornelis Dullemond

Planet formation in the solar system was started when the first planetesimals were formed from the gravitational collapse of pebble clouds. Numerical simulations of this process, especially in the framework of streaming instability, produce various power laws for the initial mass function for planetesimals. Despite the importance of this process we still are lacking a theoretical concept how to translate turbulence characteristics into the statistical properties of particle clusters, and the resulting mass function for planetesimals. Recently, a kinetic field theory for ensembles of point-like classical particles in or out of equilibrium has been applied to cosmic structure formation. This theory encodes the dynamics of a classical particle ensemble by a generating functional specified by the initial probability distribution of particles in phase space and their equations of motion. Here, we apply kinetic field theory to planetesimal formation. A model for the initial probability distribution of dust particles in phase space is obtained from a quasi-initial state for a three-dimensional streaming-instability simulation that is a particle distribution with velocities for gas and particles from the Nakagawa relations. The equations of motion are chosen for the simplest case of freely streaming particles. We calculate the non-linearly evolved density power spectrum of dust particles and find that it develops a universal $k^{-3}$ tail at small scales, suggesting scale-invariant structure formation below a characteristic and time-dependent length scale. Thus, the KFT analysis indicates that the initial state for streaming instability simulations does not impose a constraint on structure evolution during planetesimal formation.

How to cite: Shi, J., Bartelmann, M., Klahr, H., and Dullemond, C.: Kinetic Field Theory Applied to Planetesimal Formation I: Freely Streaming Dust Particles, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-149, https://doi.org/10.5194/epsc2024-149, 2024.