EXO1

How to cite: Kluska, J.: Zooming in on the place of rocky planet formation: infrared interferometric observations of protoplanetary disks, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-861, https://doi.org/10.5194/epsc2021-861, 2021.

Short-period super-Earths and mini-Neptunes have been shown to be common, yet it is still not understood how and where inside protoplanetary discs they could have formed. To form these planets at the short periods at which they are detected, the inner regions of protoplanetary discs must be enriched in dust. Dust could accumulate in the inner disc if the innermost regions accrete via the magneto-rotational instability (MRI). We developed a model of the inner disc which includes MRI-driven accretion, disc heating by both accretion and stellar irradiation, vertical energy transport, dust opacities, dust effects on disc ionization, thermal and non-thermal sources of ionization. The inner disc is assumed to be in steady state, and the dust is assumed to be well-mixed with the gas. Using this model, we explore how various disc and stellar parameters affect the structure of the inner disc and the possibility of dust accumulation. We show that properties of dust strongly affect the size of the MRI-accreting region and whether this region exists at all. Increasing the dust-to-gas ratio increases the size of this region, suggesting that dust may accumulate in the inner disc without suppressing the MRI. Overall, conditions in the inner disc may be more favourable to planet formation earlier in the disc lifetime, while the disc accretion rate is higher.

How to cite: Jankovic, M., Mohanty, S., Owen, J., and Tan, J.: MRI-accreting inner regions of protoplanetary discs, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-70, https://doi.org/10.5194/epsc2021-70, 2021.

Sticking properties are of great importance for planetesimal formation in protoplanetary disks. During the early phases of pebble growth, grains regularly travel from cold, water-rich regions to the warm inner part of the disk, experiencing ever higher temperatures. This drift leads to changes in composition, grain size, morphology, and water content. To follow the evolution that the dust might go through, we milled a meteorite to micrometer dust and tempered it under vacuum at increasing temperatures up to 1400 K. For each tempered sample we measured the splitting tensile strength of millimeter-sized dust aggregates using a well-established method known as the Brazilian test. To link the evolution of surface energy with temperature to compositional changes, we additionally measured the (ferric) composition of the samples by Mössbauer spectroscopy. 

At the low pressure of protoplanetary disks and at moderate temperatures, grains presumably hold only a monolayer of surface water and can thus be considered as dry. As the dust drifts further inwards towards higher temperature regions even this monolayer of water may evaporate completely and grains are super dry. In the laboratory, contacts between grains in cylinders are dry and remain dry for measurement if they are prepared for the Brazilian test before tempering. If cylinders are prepared after tempering but from the tempered dust, contacts are wet contacts but the influence of the composition can be traced.

For wet samples, we measured an effective surface energy which monotonously decreases by a factor of 5 from room temperature to about 1300 K due to compositional changes [1]. This reduction of surface energy still holds for dry samples but with an increase in the sticking force by a factor of ~ 10 over the wet samples. Super dry samples deviate strongly from this starting at about 900 K. Above this temperature, the surface energy is boosted and increases exponentially up to another factor of ~ 100 at about 1200 K [2].

Exceeding temperatures of 1300 K, grain sizes microscopically change (increase) for all samples, leading to an instability of aggregates and therefore making growth challenging. Beyond 1400 K no classical collisional growth is possible. 

As consequence, there is a spatial region in protoplanetary disks with temperatures around 1200 K which favors aggregation and, therefore, will likely be a sweet spot for planetesimal formation as indicated in fig.1.

[1] Bogdan, T., Pillich, C., Landers, J., Wende, H., & Wurm, G. (2020). Drifting inwards in protoplanetary discs I Sticking of chondritic dust at increasing temperatures. Astronomy & Astrophysics, 638, A151.

[2] Pillich, C., Bogdan, T., Landers, J., Wurm, G., Wende, H. (2021). Drifting inwards in protoplanetary discs II The influence of water on sticking properties at increasing temperatures. Astronomy & Astrophysics, (accepted).

How to cite: Bogdan, T., Pillich, C., Landers, J., Wende, H., and Wurm, G.: The influence of water and mineralogy on sticking properties at increasing temperatures, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-514, https://doi.org/10.5194/epsc2021-514, 2021.

Here we discuss terrestrial planet formation by using Earth and our knowledge from various isotope data such as ¹⁸²Hf-¹⁸²W, U-Pb, lithophile-siderophile elements, atmospheric ³⁶Ar/³⁸Ar, ²⁰Ne/²²Ne, ³⁶Ar/²²Ne isotope ratios, the expected solar ³He abundance in Earth’s deep mantle and Earth’s D/H sea water ratios as an example. By analyzing the available isotopic data one finds that, the bulk of Earth’s mass most likely accreted within 10 to 30 million years after the formation of the solar system. Proto-Earth most likely accreted a mass of 0.5 to 0.6 M_Earth during the disk lifetime of 3 to 4.5 million years and the rest after the disk evaporated (see also Lammer et al. 2021; DOI: 10.1007/s11214-020-00778-4). We also show that particular accretion scenarios of involved planetary building blocks, large planetesimals and planetary embryos that lose also volatiles and moderate volatile rock-forming elements such as the radioactive decaying isotope ⁴⁰K determine if a terrestrial planet in a habitable zone of a Sun-like star later evolves to an Earth-like habitat or not. Our findings indicate that one can expect a large diversity of exoplanets with the size and mass of Earth inside habitable zones of their host stars but only a tiny number may have formed to the right conditions that they could potentially evolve to an Earth-like habitat. Finally, we also discuss how future ground- and space-based telescopes that can characterize atmospheres of terrestrial exoplanets can be used to validate this hypothesis.   

How to cite: Lammer, H., Scherf, M., and Erkaev, N. V.: Terrestrial planet accretion constrained by isotopes: Implications for Earth-like habitats, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-721, https://doi.org/10.5194/epsc2021-721, 2021.

How to cite: Lichtenberg, T. and Krijt, S.: System-level fractionation of carbon from disk and planetesimal processing, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-130, https://doi.org/10.5194/epsc2021-130, 2021.

In early phases of planet formation, bouncing and fragmentation barriers still represent major obstacles. Beginning at micrometer, dust can readily grow to sub-millimeter size in collisions due to cohesion before bouncing prevails. Later, streaming instabilities trigger further growth which might finally results into planetesimal formation by gravitational collapse. However, for streaming instabilities sub-millimeter grains might be too small, therefore there is gap of at least 1 order of magnitude in size which needs to be bridged.

Here, we present our ongoing work how to bridge this gap by charge moderated aggregation [1]. When two (dielectric) grains collide they charge. This tribocharging or collisional charging is omnipresent in nature. We designed drop tower experiments in which we generated charges on glass and basalt grains by collisions in a shaker. In microgravity, the particle trajectories and collisions were observed, and charges were measured by applying an electric field.

In early work, we analyzed millimeter-sized glass grain collisions with a copper plate. The coefficient of restitution increased with the charge on a single grain due to mirror charge forces. That means highly charged grains tend to stick more easily to surfaces than uncharged grains. The velocity where sticking is possible was increased by a factor of 100 up to several dm/s [2].
 
More recently, we used half millimeter basalt spheres and observed sticking events at several cm/s among grains themselves [3]. This is also way higher than predicted by adhesion. In a number of cases, we could observe the sequential formation of aggregates of up to ten single grains. During approach the grains are accelerated due to net charge Coulomb forces but likely also due to higher order charges on the surfaces in agreement to earlier measurements of strong permanent dipole moments [4]. Attraction increases collision cross-sections and the growth is sped up. Growth only stopped by the end of microgravity [3]. 

To observe the formation of still larger aggregates we developed a new setup, in which a dense cloud of 150 µm diameter basalt grains was continuously agitated slightly under microgravity and in vacuum. Here, the growth of a giant aggregate of centimeter size was observed collecting nearly all material in one cluster [5].

To conclude, in experiments under various conditions, we see strong evidence that electrostatic charges on grains are able to conquer the bouncing barrier. We observed the bottom-up growth tracking individual particles, stable clusters emerging from dense regions and the formation of giant clusters during agitation. These are all bricks in the wall giving evidence that collisional charging might play a crucial role in planet formation.

References:

[1] Steinpilz, T.; Joeris, K.; Jungmann, F.; Wolf, D.; Brendel, L.; Teiser, J.; Shinbrot, T.; Wurm, G. Nature Physics 2020a, 16, 225-229.

[2] Jungmann, F.; Steinpilz, T.; Teiser, J.; Wurm, G. Journal of Physics Communications 2018, 2 095009, 095009.

[3] Jungmann, F.;Wurm, G. Astronomy and Astrophysics 2021, DOI: https://doi.org/10.1051/0004-6361/202039430.

[4] Steinpilz, T.; Jungmann, F.; Joeris, K.; Teiser, J.; Wurm, G. New Journal of Physics 2020b, 22, 093025.

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

How to cite: Jungmann, F., Teiser, J., Kruss, M., Steinpilz, T., Joeris, K., and Wurm, G.: Charge moderated preplanetary growth from single grains to giant aggregates, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-265, https://doi.org/10.5194/epsc2021-265, 2021.

Protoplanetary disks are thought to harbor deadzones, regions in their interior, where the ionization fraction is too low to trigger MRI turbulence. This has quite severe consequences for accretion and planet formation. 
So far, the dominant source considered for ionization is high energy radiation from external cosmic rays over stellar radiation to radioactive decay. Especially, external radiation might indeed be attenuated too much before reaching parts of the midplane in disks. Radiation might not be the only source of ionization though.

In recent years, we carried out a number of laboratory experiments on collisional charging (tribocharging) of grains related to planet formation. Being mm-size, in a range where fragmentation and bouncing dominate, these particles are large and, although charged, might not be relevant in the context of MRI themselves directly. 

An underlying assumption though is that triboelectric charge generated in collisions among grains stays on the grains. In this case, grain charging and aggregation as part of early particle growth on one side and MRI building on gas ionization on the other side would be distinct processes. However, what we recently found in a number of different experiments, is that tribocharging of grains also charges the ambient gas.

In one set of microgravity experiments, we observed that the charge on two particles before and after a collision is not conserved. On the order of 20\% of the pre-charge on a grain is discharged into the environment. To mention a second experiment, the number of ions detected in a gas flow after passing a granular medium increases strongly if the particles undergo collisions, i.e. are charged. There are experiments with further evidence but these two clearly show that charge is leaking into the ambient atmosphere during collisions.

In detail, the charging depends on the collision frequencies and particle sizes, which are model dependent. We also caution that these are only first experiments in this direction, but, in any case, estimates suggest that ionization rates within the gas might regularly be way larger than e.g. provided by radiation at the surface of a disk. If this holds, the charge balance in the midplane of protoplanetary disks might be quite different than previously assumed. The obvious and severe consequence might simply be that there are just no deadzones.

How to cite: Wurm, G., Jungmann, F., van Unen, H., Voellings, N., Schoenau, L., and Teiser, J.: Does Leakage of Charge in Particle Collisions Kill the Concept of Deadzones?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-219, https://doi.org/10.5194/epsc2021-219, 2021.

A notable challenge of planet formation is to find a path to directly form planetesimals from small particles. Small particles are, in general, challenged to grow beyond meter size due to the “growth barrier” and the “drift barrier”.

Over the last few decades, magnetohydrodynamic (MHD) simulations have shown that a region where ionization is too low for the magneto-rotational instability (MRI) to operate (i.e., a “dead zone”) might ubiquitously exist in the inner part of the disk midplane, and that only surface layers are magnetically active, supporting accretion. These indicate a nonuniform turbulence structure.

In this study, we aim to understand how drifting pebbles pile up in a protoplanetary disk with a nonuniform turbulence structure (Figure 1). We consider a disk structure in which the midplane turbulence viscosity (i.e., diffusion of pebbles is characterized by a distinct non-dimensional parameter (α_mid)) increases with the radius in protoplanetary disks, such as in the outer region of a dead zone. We consider that the gas accretion toward the central star is characterized by a distinct non-dimensional parameter (α_acc). We perform 1D diffusion-advection simulations of pebbles that include back-reaction (the inertia) to the radial drift and the vertical and radial diffusions of pebbles for a given pebble-to-gas mass flux (F_p/g).

We report a new mechanism, the “no-drift” runaway pile-up (i.e., instability), that leads to a runaway accumulation of pebbles in disks, thus favoring the formation of planetesimals by streaming and/or gravitational instabilities. This occurs when pebbles drifting in from the outer disk and entering a dead zone experience a decrease in vertical turbulence. Consequently, the scale height of the pebble then decreases, and, for small enough values of the turbulence in the dead zone and high values of the pebble-to-gas flux ratio, the back-reaction of pebbles on gas leads to a significant decrease in their drift velocity and thus their non-steady-state accumulation (i.e., a local runaway pile-up of pebbles). This process is independent of the existence of a pressure bump and/or pebble growth.

Figure 1: Schematic illustration of pebble drift and its pile-up within a protoplanetary disk with a dead zone. The disk gas accretion is characterized by alpha-parameter (α_acc), while the midplane diffusivity, being a dead zone (α_dead << α_acc) in the inner region, is characterized by α_mid. During the inward drift of pebbles, the pebble scale height H_p decreases as H_p is proportional to α_acc^1/2 until a KH instability prevents it from becoming smaller. A smaller H_p leads to an elevated local midplane concentration of pebbles within a thinner midplane layer. The elevated midplane pebble-to-gas ratio causes the back-reaction to be more effective in reducing the radial drift velocity of pebbles. Such a physical interplay with a sufficiently large pebble-to-gas mass flux results in a continuous accumulation of pebbles in a runaway fashion (i.e., the “no-drift” runaway pile-up). Redrawn from Hyodo, Ida, Guillot (2021) A&A, 645, L9.

How to cite: Hyodo, R., Ida, S., and Guillot, T.: Planetesimal formation by the “no-drift” mechanism, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-161, https://doi.org/10.5194/epsc2021-161, 2021.

    Large scale vortices are thought to be natural outcomes of hydrodynamic instabilities in protoplanetary disks, as for instance the Rossby Wave Instability [1] or Baroclinic instability. Analytical and numerical studies showed that they can be long-lived and catalyze efficiently dust material concentration (e.g) [2], [3] and encourage to think they could play a role in protoplanetary-disk evolution and planetesimal formation. Their presence in the outer regions of circumstellar disks is possibly betrayed by recent observations of lopsided structures with ALMA and VLT [4], [5] and raises also a question: what is the importance of disk self-gravity on their structure and evolution.

    We present 2D hydrodynamical simulations of steady vortices evolving under the effect of their own gravity. The goal is to study their evolution and the possibility of gravitational collapse. Are particularly addressed the structure, migration, mass, and physical variables characterizing these self-gravitating structures. We also pay special attention to the case of very massive vortices.

Figure 1. From left to right: Rossby number and density (in log scale) perturbations induced by a large scale vortex after 171 orbital periods at 7.5 AU.

[1] Lovelace, R. V. E., Li, H., Colgate, S. A., & Nelson, A. F. 1999, ApJ, 513, 805

[2] Barge, P. & Sommeria, J. 1995, A&A, 295, L1

[3] Raettig N, Klahr H Lyra W, 2015, ApJ804

[4] Tsukagoshi, T., Muto, T., Nomura, H., et al. 2019, ApJ, 878, L8

[5] Dong, R., Liu, S.-y., Eisner, J., et al. 2018, ApJ, 860, 124

How to cite: Rendon Restrepo, S. and Barge, P.: Selfgravitating vortices in protoplanetary disks, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-697, https://doi.org/10.5194/epsc2021-697, 2021.

    Large scale vortices are thought to be natural outcomes of hydrodynamic instabilities in protoplanetary disks, as for instance the Rossby Wave Instability [1] or Baroclinic instability. Analytical and numerical studies showed that they can be long-lived and catalyze efficiently dust material concentration [2], [3] what encourages to think they could play a role in protoplanetary-disk evolution and planetesimal formation. Their presence in the outer regions of circumstellar disks is possibly betrayed by recent observations of lopsided structures with ALMA and VLT [4], [5].

    We present our latest results of two-phase 3D numerical simulations in which the solid particles are embedded in the gas and described as a second pressureless fluid.  The goal is to discuss the sedimentation of the dust phase in the protoplanetary disk midplane, and the dust trapping mechanism induced by 3D vortices. We will also address the question if 3D vortices are more stable to the streaming instability than 2D vortices.

Figure 1. Left : Three 3D vortices generated by the Rossby Wave instability. Right : Same as left but two vortices merged after few orbital periods

[1] Lovelace, R. V. E., Li, H., Colgate, S. A., & Nelson, A. F. 1999, ApJ, 513, 805

[2] Barge, P. & Sommeria, J. 1995, A&A, 295, L1

[3] Raettig N, Klahr H Lyra W (2015), ApJ804

[4] Tsukagoshi, T., Muto, T., Nomura, H., et al. 2019, ApJ, 878, L8

[5] Dong, R., Liu, S.-y., Eisner, J., et al. 2018, ApJ, 860, 124

How to cite: Rendon Restrepo, S. and Barge, P.: 3D simulations of dust trapping in gaseous vortices, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-814, https://doi.org/10.5194/epsc2021-814, 2021.

In this talk I will review our current understanding of planet formation on the outer parts of the protoplanetary disk. We will address questions such as: what type of planetary compositions do we expect? What are the differences with planet formation in the inner disk? Is there a type of planet formation model (e.g pebble vs. planetesimal accretion) that provides a better match with observations? Are there observational trends that we cannot explain? What theoretical challenges do we still face? What new observational constraints will arise in the next years? 

How to cite: Venturini, J.: Planet formation on the outer disk, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-862, https://doi.org/10.5194/epsc2021-862, 2021.

In the current theories of planet formation, the amount of energy that a forming gas giant retains from its accretion flow is still unknown. This unconstrained parameter has a large impact on the post-formation evolution of the new planet, as it defines its initial temperature and luminosity. Models have been developed, ranging from “hot-start” models assuming that all the energy is retained internally, to “cold-start” ones assuming that everything is radiated away, and "warm-start" ones in between. Their coexistence introduces large degeneracies on the determination of age and mass in direct imaging observations, as these studies use the cold or hot-start models to infer these parameters from the observed luminosity of a planet. A promising way of solving this problem is the study of atomic emission lines originating from the hot gas shocked by the accretion flow. Recently, Aoyama et al. (2018, 2020) presented simulations of hydrogen lines emitted by the accretion shock onto the circumplanetary disk and the planetary surface. They showed that the line luminosity and width can be used to infer the protoplanet mass, thus giving an estimation that is independent from the evolution models. They applied it to the case of PDS70 b and c (Aoyama & Ikoma 2019, Hashimoto et al. 2020), but were ultimately limited by the spectral resolution of the MUSE observations they used (R ~ 2500). In this context, our team recently proposed and carried out a pilot program using the VLT/ESPRESSO fiber-fed spectrograph, equipped with very high resolution (R = 190 000), to characterize the Hα line of the young substellar companion GQ Lup b. We will present in this poster how these observations were conducted, the methods used to remove the contamination from the host star, and the results we obtained.

How to cite: Houllé, M., Sedaghati, E., Figueira, P., and Vigan , A.: A high-resolution search for the Hα emission line of the accreting companion GQ Lup b with ESPRESSO, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-833, https://doi.org/10.5194/epsc2021-833, 2021.

In close two-body astrophysical systems, like Hot-Jupiter systems, tidal interactions often drive the dynamical evolution of the system on secular timescales, modifying body spins and the orbit of the planet (e.g. Mathis 2019). Most stars around which planets have been discovered are cool stars and feature a convective envelope which is magnetised, as shown by ground-based Zeeman broadening/Doppler imaging techniques and 3D (magneto-)hydrodynamical simulations. Moreover, strong surface magnetic fields have also recently been inferred through star-planet interaction in Hot-Jupiter giant gaseous planets (e.g. Cauley et al. 2019). Due to the tidal potential of the companion (star or planet), tidal flows are generated in the convective layers and dissipated through friction mechanisms, like viscous or Ohmic turbulent damping (e.g. Duguid et al. 2020, Astoul et al. 2019). This tidal dissipation leads to the redistribution and exchange of angular momentum in the convective shell and with the companion, respectively. In the most compact systems, non-linear effects are likely to have a significant impact on the tidal dissipation and change the zonal flows triggering differential rotation, as shown in the hydrodynamical study of Favier et al. (2014).

In this context, we also investigate how the addition of non-linearities affect the tidal flow properties, the energy and angular momentum balances, thanks to 3D (magneto-)hydrodynamic non-linear simulations of an adiabatic and incompressible convective shell. In our neutrally-stratified model, the action of convective eddies on tides is simply taken into account through an effective viscosity. Moreover, we have chosen a body forcing where the equilibrium tide (the quasi-hydrostatic tidal flow component) acts as an effective force to excite tidal waves, while using stress-free boundary conditions. As a result, our perturbed flow is decomposed into a non-wave like part (the equilibrium tide) plus (magneto-)inertial waves. In that respect, our model differs from the above mentioned study which is using an incoming radial flow at the surface to excite inertial waves. In particular, within our more realistic set-up, we are able to identify and assess the importance of the different types of non-linearities (wave/wave, non wave-like/non wave-like, or mixed), and thus discuss unphysical contributions leading to non expected angular momentum evolution for some simulations observed in Favier et al. (2014). By removing these contributions, we also demonstrate that differential rotation can develop in the shell (left figure, azimuthal velocity in a meridional cut) due to the anisotropic deposition of angular momentum in hydrodynamical simulations (right figure, kinetic energy in a meridional cut), which would not be the case in magneto-hydrodynamic simulations according to our early results. Moreover, we show new results for the amplitude of the energy stored in these zonal flows, as well as angular momentum evolution. In particular, we find that non-linearities tends to smooth the frequency dependence of tidal dissipation by lowering it compared to linear predictions (as in Jouve & Ogilvie 2014 using a Cartesian box). As the dissipation of tidal waves in convective envelopes is a major part of total tidal dissipation for close low-mass stars and giant gaseous planets, the inclusion of non-linear effects in its estimation can deeply modify the tidal efficiency (the tidal quality factor) and the associated tidal migration/spins timescales.

How to cite: Astoul, A. and Barker, A.: Non-linear effects on tides in the convective envelope of low-mass stars and giant gaseous planets, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-813, https://doi.org/10.5194/epsc2021-813, 2021.

Introduction:

Roughly 50 % of solar-like stars are part of binary star systems. Yet, only about 180¹ of the nearly 4700 exoplanet candidates are part of a binary or multiple star system.
Yet, not all of the known planets in binary systems are in coplanar orbits. Some are misaligned with respect to the binary star orbital plane up to 90◦ (see catalogue¹).
We want to investigate the late stages of terrestrial planet formation in binary star systems, with special emphasis on the dynamical evolution of the embryo planetesimal disks. We restrict ourselves to S-type motion, meaning the disk objects orbit only the primary star. To take the effects of gravitational interactions among disk objects into account a massive parallelized force calculation is applied, which has been recently developed by one of the authors [4]. The planar binary-star-disk configuration defines our reference plane. For simplicity the binary stars are inclined instead of aligning the disk objects on various inclinations.

Methods and Setup:

For solving the equation of motions the Bulirsch-Stoer (BS) method is applied. It is an extrapolation method which takes different results for a timestep τ for the extrapolation of a result for “infinity“ substeps. Furthermore, the method is massively parallelized on graphical processing units (GPU).
The collisions among disk objects are handled so-far with the so-called “perfect merging“. This setup allows simulations up to 10000 gravitational interacting disk objects for about 1 Myr in a reasonable computation time.
The intial setups for the equal mass binary star systems are shown in table 1.

Table 1: Initial parameters of the binary star systems

The circumprimary planetesimal disk extends between 1 and 4 au and is initially dynamically cold. For the given binary star systems the disk lies within the area of stable motion [2]. In this study the simulations have been performed using 2000 planetesimals and 25 planetary embryos for a time of 1 Myr for each binary stars listed in table 1.

Results:

The simulations of inclined tight binary stars (a_b = 30 au) show an oscillation of the planetesimals’ and embryos’ inclination about binary stars inclination between i_min = 0° to i_max = 2 · i_b although the disk was dynamically cold at the beginning of the simulation. Figure 1 shows the case for i_b = 20°.

Figure 2 shows the inward migration of the planetary embryos in the case of i_b = 45° . This effect seems to be stronger for the planetary embryos which are located in the inner part of the disk (a < 2 au) as well as for higher inclinations of the binary stars.

Summary and Conclusions:

We investigated the dynamical evolution of misaligned (=ˆ variation in the inclination of the binary stars) protoplanetary disks for various binary star configurations with planetesimal disks containing about 2025 mutual gravitational interacting objects.
This study showed that in the case of inclined tight binary stars case the rapid increase in the inclination of the disk objects slows down the planetary embryos growth compared to the coplanar case [4]. Additionally, the planar case shows an outward migration of the outer planetasimals, while the inclined systems indicate an inward migration of planetary embryos (see figure 3), which is possibly caused by Kozai migration [3].

Acknowledgements

M.Z. and E.P-L want to acknowledge the support by the Austrian FWF - project no. P33351-N.

References

• [1] Jensen, E. and Akeson, R.: Misaligned protoplanetary disks in a young binary star system. Nature 2014, Vol. 511, pp 567-569
• [2] Pilat-Lohinger, E. and Dvorak, R.: Stability of S-type orbits in binaries. Celestial Mechanics and Dynamical Astronomy 82.2, pp. 143-153, 2002
• [3] Wu, Y., Murray, N.: Planet migration and binary companions: The case of HD 80606B. The Astrophysical Journal, 589, pp. 605-614, 2003
• [4] Zimmermann, M.: The influence of binary systems on planetesimal disks. Master thesis, University of Vienna, 2021

How to cite: Zimmermann, M. and Pilat-Lohinger, E.: Dynamical evolution of planetesimal disks in inclined binarystar systems, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-376, https://doi.org/10.5194/epsc2021-376, 2021.

Abstract

We aim to understand the impact of different refractory element ratios such as Mg, Si, and Fe on the composition of planets. We use the thermodynamic equilibrium code GGchem to simulate the condensation of solids in a minimum mass solar nebula around main sequence G-type stars within 150pc. We extract the stellar elemental composition from the Hypatia database. We find that a lower Mg/Si ratio shifts the condensation sequence from forsterite and SiO to enstatite and quartz; a lower Fe/S ratio leads to the formation of FeS and FeS₂ and little or no Fe-bearing silicates. Ratios of refractory elements translate directly from the gas phase to the condensed phase for T<1000K. However, ratios with respect to volatile elements (e.g. oxygen and sulphur) in the condensates – the building blocks of planets – differ from the original stellar composition. Our results can have important implications for planet interiors, which depend strongly on the degree of oxidization and the sulphur abundance.

1. Introduction

Planets form from solid material residing in the disk around a young star. Both the star and the disk are composed oft he same material (inherited from the collapsing cloud). In the inner disk (inside a few au), material is likely sublimating and solidifying repeatedly due to episodic accretion events and stellar luminosity peaks. Small variations from solar abundances (within 0.5dex), especially also for refractory elements, are ubiqutous in the solar neighborhood. The question is whether such small element abundance fluctuations have a noticeable impact on the composition of a planet condensing from the planet forming disk.

2. Methods

We selected from the Hypatia Database [4] single solar-type main-sequence stars within 150 pc. We select stars that have as complete as possible chemical abundance data and draw six sample stars, representative of the typical spreads in the elements ratios (see Fig. 1).

Figure 1: Ratios of the refractory elements Mg, Si and Fe, as well as S, for main-sequence G-type stars within 150pc. Black dots represent the location of the six sample stars. A red dot indicates a star for which we inferred missing abundances from the median of the known abundances. 

We use the GGchem code developed by [2] and re-written and updated by [6]. The thermo-chemical data are taken from the NIST-JANAF and the geophysical SUPCRTBL databases. The code has been successfully benchmarked against the public TEA code [1]. Given a specific temperature and pressure, the code calculates the various molecules and condensates forming by minimizing the Gibbs free energy. We choose 24 elements (H, He, Li, C, N, O, Na, Mg, Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Zr, W, F, P), leading to 552 molecules and 241 condensates. We use the pT-profile of the Minimum Mass Solar Nebula from [3] and assume that different parts of the disk do not mix and that planets are forming in situ. 

We sample the results of the condensation sequences by defining locations for the formation of hypothetical planets. Besides the current locations of Mercury, Venus, Earth, Mars, and the Asteroid belt in the Solar system, we also use 1000, 1250 and 1500K, mimicking that solar system planets likely formed at higher temperatures (dynamical evolution).

Figure 2: Condensation sequence for Mg-bearing species for the solar abundances and two extreme cases of Mg/Si ratio.

Figure 3: The element ratios in the condensed phase from which the hypothetical planets form (noted in legend by their respective temperatures). Ratios are normalised to the Solar values. The x-axis label represents the solar composition (0) and the six sample stars. The black horizontal line represents the initial value of the gas phase ratio.

3. Condensation sequences

Figure 2 shows the condensates containing magnesium for our six sample stars as a function of temperature. Iron condenses as metallic Fe at very high temperature, removing it from the gas phase. For solar abundances of Mg and Si, forsterite and enstatite are both abundant down to ~400K. Below that, they start to combine with hydrogen and form more complex silicates. This behavior is highly dependent on the initial Mg/Si ratio. At a high Mg/Si ratio of 0.17dex, forsterite stays the most abundant condensate down to 240K; enstatite, quartz and SiO are absent. For a low Mg/Si ratio of -0.26dex, the high temperature condensates are SiO and forsterite; below ~1250K, we find instead SiO₂ and enstatite. For Fe/S≥-0.25dex, iron forms at low temperatures various types of Fe-bearing silicates while for Fe/S≤-0.67dex, Fe only forms FeS and FeS₂.

4. Planet composition

Figure 3 shows that the refractory elements are directly inherited from the gas phase. This is not true for more volatile species such as sulphur and oxygen. Planets forming from condensates at temperatures ³1000K do not show much S, because the lowest temperature condensate FeS forms at ~700K. Planets form at ³250K, inside the snow line, in an environment where a fraction of the oxygen remains in the gas phase, leading to condensates with higher refractory/oxygen ratios. Planets forming outside the snow line can obtain ratios equal to the initial gas phase.

5. Conclusions

Our results show that planets could have more reduced interiors and an Fe/S ratio different from the initial gas phase. This can alter the planets interior structure [5]. In conclusion, we show that the typical spread (0.1-0.2dex) in the abundance of refractory elements in the Solar neighbourhood does impact significantly the outcome of planet formation.

Acknowledgements

This research was supported and inspired by discussions through the ISSI International Team collaboration "Zooming In On Rocky Planet Formation" (team 482).

References

[1] Blecic, J., Harrington, J., Bowman, M.O. 2016, ApJS, 225, 4

[2] Gail, H.P., Sedlmayr, E. 1986, A&A, 166, 225

[3] Hayashi, C. 1981, in IAUS, Vol. 93, ed. D. Sugimoto, D.Q. Lamb, D.N. Schramm, 113–126

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[5] Hirose, K., Labrosse, S., Hernlund, J. 2013, Annual Review of Earth and Planetary Sciences, 41, 657

[6] Woitke, P., Helling, C., Hunter, G.H., et al. 2018, A&A, 614, A1

How to cite: Jorge, D., Kamp, I., Waters, R., Woitke, P., and Spaargaren, R.: Forming planets around stars with non-solar composition, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-853, https://doi.org/10.5194/epsc2021-853, 2021.

The composition of a planet atmosphere is heavily influenced by the planet formation process and subsequent evolution. In this context, planet formation models can provide us with vital information on how different assumptions and conditions would affect the planet compositions. The combination of these models with atmospheric models are then very strong tools to help us interpret observations and connect atmospheric traits to the planet formation model. 

In this work, we developed a framework that uses models for protoplanetary disks and planet formation that parametrizes the inputs in simple manners and forms giant planets with their atmospheres. Using this framework, we simulate a large population of planets with the same final planet mass and orbit distance, with different initial forming conditions. This allows us to study the trends that explain how the formation process affects the composition of giant planets. Our simulation allows us to study the effects of migration and in situ formation on the planet composition. Figure (1) shows a hundred thousand planets with one Jupiter mass at a distance of 0.02 AU. Each point on these plots represents a different initial condition. Top right plot shows the influence of the amount of dust grains, solids with a stokes number less than one, on the metallicity and the C/O ratio. Top left plot shows the influence of planetesimals, solids with a stokes number much higher than one, on the metallicity and C/O ratio. Th bottom plot shows the influence of the initial orbital distance on the C/O ratio and the metallicity of the planet.

This plot shows that the solid size distribution in the disk has an important role in causing the planet metallicity and C/O ratio changes between sub-solar and super solar. Planets that are formed in disks where the majority of the solids has a stokes number lower than 1, will end up with a more solar or sub-solar metallicity and solar to super-solar C/O ratio. On the other hand, planets that are formed in disks where the majority of the solid has a stocks number much higher than one, will end up with a more super-solar metallicity and sub-solar C/O ratio. In addition we show that the C/O ratio together with the metallicity of the planets with super-solar metallicity, can put a lower limit on the initial orbit where the planet initiates migration type II. In order to study planets with solar and sub-solar metallicity, we suggest that it is important to look at atomic ratios such as S/N, Si/N, Fe/N, or Mg/N.

To have a comprehensive understanding of the connection between disk and planet atmospheres, we couple our model describe above to an atmospheric retrieval model. We retrieve the formation parameters that we introduce in our formation model from the observed spectra for different planets. We then look at how planet characteristics, such as its mass, radius, orbital distance, and atmospheric condition affect the possibility of retrieving their formation history.

Our formation model in combination with atmospheric models, provides a strong tool in combination with space missions such as ARIEL and JWST. In particular, with JWST we can obtain information about the building blocks of exoplanet atmospheres from observing the planets themselves and the disks in which they are formed and compare them to our model predictions in order to constrain planet formation scenarios from their atmospheric composition. Additionally, our model can be used to inform the target list for ARIEL as it predicts for which planets it is more likely to retrieve information about their formation history.

How to cite: Khorshid, N., Min, M., Desert, J. M., Dominik, C., and Woitke, P.: Planet formation and its effect on planetara atmosphere composition, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-660, https://doi.org/10.5194/epsc2021-660, 2021.

With new and upcoming observing facilities (JWST and the ELTs), the exoplanet community is poised to precisely measure the chemical inventory of exoplanet atmospheres. This will allow, for the first time, to start investigating whether one of the greatest promises of atmospheric characterization studies holds up: inverting the atmospheric composition to infer the planet formation history encoded in it. In my talk, I will show how such measurements allow to run so-called formation retrievals, which constrain a planet’s formation history using its atmospheric abundances in a Bayesian retrieval framework. I will demonstrate how simple and popular models for the composition of the protoplanetary disk and planet formation could lead to interesting insights when applied in formation retrievals. At the same time, I will discuss how such assumptions are too strongly simplified for making the exoplanet atmosphere — formation connection in practice, and what the most pressing theoretical challenges are. Achieving this connection will be a formidable and interdisciplinary challenge, but the exciting exoplanet observations that lie ahead will allow the community to tackle it in earnest.

How to cite: Mollière, P., Molyarova, T., Bitsch, B., Eistrup, C., Burn, R., Nasedkin, E., Henning, T., Semenov, D., Mordasini, C., Kreidberg, L., Schlecker, M., Lacour, S., and Nowak, M.: From atmospheric to exoplanet formation retrievals, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-801, https://doi.org/10.5194/epsc2021-801, 2021.

The Kepler mission revealed that sub-Neptunes are about as common as stars. Sub-Neptunes have sizes between rocky terrestrial and gassy giant planets; their discovery defied our pre-existing notion of planet demographics. The prevailing view for sub-Neptunes was that they are mostly core by mass and atmosphere by volume [1]. (Although the alternative explanation that sub-Neptunes are waterworlds has not been ruled out [2], it does not explain the radius distribution with orbital period nor the densities of highly irradiated planets, among other problems, and so it is disfavored [3]). However, the current formation models lack material properties data (e.g. solubilities) for their core-atmosphere interface.

However, the temperature and pressure at the magma-atmosphere interface can rise to >3000 K and ~5-30 GPa [4][5], high enough for dissolution of hydrogen gas into the magma [6][7]. Thus, sub-Neptune magma oceans at the core-atmosphere interface are abundant, long-lived [8], and massive [9]. The dissolution of atmosphere into the magma may explain the drop-off in exoplanet abundance at 3 times Earth radius, but the puff-up of the magma due to gas dissolution was not included.

We propose a simple model to calculate sub-Neptune mass-radius relation including the puff-up effect. Key assumptions include: (1) the Fe/core mass fraction is Earth-like, and He/gas mass fraction is Solar-like; (2) photospheric radius is 6 scale heights above the radiative-convective boundary (RCB); (3) ideal mixing between the dissolved gas and magma; (4) the dissolved gas is well mixed over the silicate-layer, within which the temperature gradient is controlled by the properties of magma; (5) nonlinear solubility is constrained by limited laboratory data [9]. The equations-of-state (EoS) used are a Mg₂SiO₄ for the magma [10]; the H/He EoS [11]; and a simple model for Fe [12]. The model is integrated from the RCB and evolves until magma-atmospheric solubility equilibrium.

We have varied the core mass, atmospheric mass and equilibrium temperature in the atmosphere. Our preliminary results are shown in Figures. The critical point for the puff-up of the core due to the dissolved gas corresponds to ~1% solubility at the magma-atmosphere boundary (Fig. 1). The puff-up effect turns out to be important up to 0.3 Earth radius (Fig. 2), .e.g, much larger than the radius error bars for a single planet in the CKS survey with Gaia DR2 data [13].

Figure 1: The solubility of gas at the magma-atmosphere interface as a function of temperature and pressure, assuming ideal gas mixture. Lines correspond to atmospheric profiles of sub-Neptunes with core masses of 10 Earth masses, situated at 0.1 AU from their host stars.

Figure 2: Mass-radius relation of the core. Subscripts represent conditions at the magma-atmosphere interface. The blue curve is more representative of sub-Neptunes, while the red curve coincides with an air-less rocky planet (black).

In future, we will add additional constrain on gas/core mass fraction [14], forward-model the relationship between mass and photospheric radius (the observables), and generate early predictions for exoplanet masses and radii that can be used to help interpret data such as ESA’s PLAnetary Transits and Oscillations of stars (PLATO) and NASA’s Transiting Exoplanet Survey Satellite (TESS).

[1] Lopez, E. D., & Fortney, J. J. (2014). Understanding the mass-radius relation for sub-Neptunes: Radius as a proxy for composition. The Astrophysical Journal, 792(1), 1.

[2] Mousis, O., Deleuil, M., Aguichine, A., Marcq, E., Naar, J., Aguirre, L. A., ... & Gonçalves, T. (2020). Irradiated ocean planets bridge super-earth and sub-Neptune populations. The Astrophysical journal letters, 896(2), L22.

[3] Bean, J. L., Raymond, S. N., & Owen, J. E. (2021). The nature and origins of sub‐Neptune size planets. Journal of Geophysical Research: Planets, 126(1), e2020JE006639.

[4] Lee, E. J., Chiang, E., & Ormel, C. W. (2014). Make super-Earths, not Jupiters: Accreting nebular gas onto solid cores at 0.1 AU and beyond. The Astrophysical Journal, 797(2), 95.

[5] Piso, A. M. A., Youdin, A. N., & Murray-Clay, R. A. (2015). Minimum core masses for giant planet formation with realistic equations of state and opacities. The Astrophysical Journal, 800(2), 82.

[6] Chachan, Y., & Stevenson, D. J. (2018). On the Role of Dissolved Gases in the Atmosphere Retention of Low-mass Low-density Planets. The Astrophysical Journal, 854(1), 21.

[7] Kite, E. S., Fegley Jr, B., Schaefer, L., & Ford, E. B. (2019). Superabundance of Exoplanet Sub-Neptunes Explained by Fugacity Crisis. The Astrophysical Journal Letters, 887(2), L33.

[8] Vazan, A., Ormel, C. W., & Dominik, C. (2018). Effect of core cooling on the radius of sub-Neptune planets. Astronomy & Astrophysics, 610, L1.

[9] Kite, E. S., Fegley Jr, B., Schaefer, L., & Ford, E. B. (2020). Atmosphere origins for exoplanet sub-Neptunes. The Astrophysical Journal, 891(2), 111.

[10] Hirschmann, M. M., Withers, A. C., Ardia, P., & Foley, N. T. (2012). Solubility of molecular hydrogen in silicate melts and consequences for volatile evolution of terrestrial planets. Earth and Planetary Science Letters, 345, 38-48.

[11] Stewart, S., Davies, E., Duncan, M., Lock, S., Root, S., Townsend, J., ... & Jacobsen, S. (2020, November). The shock physics of giant impacts: Key requirements for the equations of state. In AIP Conference Proceedings (Vol. 2272, No. 1, p. 080003). AIP Publishing LLC.

[12] Chabrier, G., Mazevet, S., & Soubiran, F. (2019). A new equation of state for dense hydrogen–helium mixtures. The Astrophysical Journal, 872(1), 51.

[13] Seager, S., Kuchner, M., Hier-Majumder, C. A., & Militzer, B. (2007). Mass-radius relationships for solid exoplanets. The Astrophysical Journal, 669(2), 1279.

[14] Fulton, B. J., & Petigura, E. A. (2018). The California-Kepler survey. VII. Precise planet radii leveraging Gaia DR2 reveal the stellar mass dependence of the planet radius gap. The Astronomical Journal, 156(6), 264.

[15] Lee, E. J. (2019). The boundary between gas-rich and gas-poor planets. The Astrophysical Journal, 878(1), 36.

How to cite: Fan, B., Lee, E., and Kite, E.: Magma-atmosphere interactions impact mass-radius relation of sub-Neptunes, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-157, https://doi.org/10.5194/epsc2021-157, 2021.