Author(s): Kaustubh Hakim

Abstract:

This decade is witnessing a major shift from the detection of exoplanets to the characterization of their atmospheres. From mass-radius measurements that inform about bulk planet composition, we are moving to detailed atmospheric spectroscopy that unravels atmosphere composition. While the observations of atmospheres of intermediate-sized and small exoplanets keep growing, the understanding of planetary interiors and interior-atmosphere interactions is more vital than ever. In this overview talk, I will focus on terrestrial-type exoplanet interiors and evolution from a perspective of chemical and physical diversity. The interior composition, mineralogy and structure are largely determined by the inventory of refractory elements. The interior evolution and atmospheric chemistry are further influenced by the inventory of volatile elements. I will discuss the role of exoplanet interiors on the composition of atmospheres including processes such as geochemical cycling, outgassing and atmospheric escape. Going forward, we will need to develop a thorough understanding of planetary mineralogy, material properties and processes that take place outside the physical and chemical realms of Earth and planetary bodies in the Solar System with the help of theoretical models and laboratory experiments.

Author(s): Nader Haghighipour

Abstract:

The discovery of multi-planet resonant chains such as those in TRAPPIST-1 and Kepler-90, where adjacent planets are in different resonances, has raised questions on the formation of these systems. It is widely accepted that these systems formed through the combination of migration and resonance-capture where migrating planets capture each other in resonances. There is, however, an issue with this scenario as migrating planets tend to capture each other in the same resonance. It has been suggested that tidal forces are the reason that resonant-chain planets are in different commensurabilities. The latter motivated us to examine the validity of this statement. We have carried out extensive simulations of planet formation and migration, and determined the probability of capture for different resonances. Results demonstrate that migrating planets can in fact be captured in different resonances confirming that the diversity of resonances observed in resonant chains is a natural consequence of the formation and resonance capture mechanism, and does not require a secondary, post-formation process. Results also show that the probability of capture (and, therefore, the final commensurabilities) is highly depended on the characteristics of the systems, especially the planets’ mass-ratio and migration speed. Finally, our simulations indicate that capture in a resonance never occurs at the resonance’s exact commensurability and there is always some deviation. The extent of this deviation also depends on the mass-ratio and orbital characteristics of the planets and the mechanism through which migrating planets lose energy. This also confirms that unlike previous studies, no post-capture mechanism is needed to explain the deviation from exact resonances observed in Kepler (and RV) planet pairs. We present the details of our study and discuss their implications for the formation and orbital architecture of resonant, multi-planet systems.

Author(s): Yiannis Tsapras

Abstract:

Microlensing is the third most successful method in discovering exoplanets with a unique sensitivity to planets at large orbital separations.

I will present the basics of the method, show some recent results and discuss what is in store for the future.

References

Tsapras, Y. et al. (2019) Publications of the Astronomical Society of the Pacific, Volume 131, Issue 1006, pp. 124401

Tsapras, Y. (2018) Geosciences, vol. 8, issue 10, p. 365

While planet formation theories have been traditionally constrained by the masses and orbital distance distributions of exoplanets, we are now entering an era where additionally constraints from planetary atmospheres become available. These constraints are mostly on the C/O, C/H, O/H and water abundance of planets. Classical planet formation scenarios (without pebble evaporation) can only reproduce super-solar atmospheric abundances via the accretion of planetesimals. In these models, sub-solar atmospheric abundances then require no solid accretion, opening the question why certain planets should accrete planetesimals and others should not. In contrast, our model (Schneider & Bitsch 2021a,b) including pebble drift and evaporation in the disc as well as planet growth via pebble and gas accretion while the planets migrate can explain the formation of giant planets with super-solar and sub-solar abundances without additional solid accretion. These differences arise from the formation location of the planet in respect to ice lines, where planets closer in can accrete more evaporated volatiles compared to planets further out. I will highlight how our model can match the measured super-solar atmospheric abundances of tau Boötis b and the measured atmospheric sub-solar abundances of WASP-77A-b and what this implies for their formation history.

References

Schneider, A. D. & Bitsch, B. 2021a, A&A, 654, A71
Schneider, A. D. & Bitsch, B. 2021b, A&A, 654, A72

Author(s): Sarah Rugheimer

Abstract:

This planet we call home is teeming with life from the very depths of the ocean where no light penetrates, to small brine layers between ice crystals and near-boiling iridescent waters of Yellowstone. As we discover the vast diversity of extremophile life on Earth, our minds can only begin to imagine the possibilities for life to exist on other planets in the Universe. We can search for life on exoplanets and in our Solar System, each approach can inform the other. As we learn more about habitable environments we can use that information to contextualize observations of exoplanet atmospheres with JWST and future missions. And eventually, exoplanet observations may provide a statistical understanding of the nature and origins of life. In this review talk I will present how the lessons we are learning from planetary habitability and exoplanets can work synergistically together.

Author(s): Remo Burn, Christoph Mordasini, Lokesh Mishra, Jonas Haldemann, Julia Venturini, Alexandre Emsenhuber and Thomas Henning

Abstract:

We present a new take on the highly discussed demographic feature in the radius distribution (Fulton & Petigura, 2018) of observed exoplanets, the „radius valley“, using population syntheses. The conventional explanation is the loss of primordial H/He envelopes from rocky cores. In contrast to our earlier work (Jin & Mordasini, 2018), we cannot reproduce a clear valley with the standard multi-planet simulations (Emsenhuber et al. 2021). The difference to older models are a larger diversity in core compositions and H/He which arises when accounting for N-body effects, e.g. collisions.
Exploring this by means of several new simulations with improved physics, we found that we recover the radius valley at the observed position if we include steam atmospheres in combination with photoevaporation of both H/He and water. The exclusion of the gaseous phase of water was a shortcoming of previous models and is key for the population of observed, hot exoplanets. We determine that three effects are at play: First, Type I migration moves a population of icy planets, corresponding to the observed sub-Neptunes, to the inner system. Due to their ability to grow from a larger mass reservoir and only migrating above a threshold mass, their masses are larger than the dry, rocky planets which formed in the inner system, making up most of the Super-Earths. Second, the phase change of the water contained in the migrated sub-Neptunes separates this population from the rocky planets. Without this effect the scatter in initial disk conditions would fill up the radius gap. Lastly, photoevaporation of both water and H/He removes planets from regions where they contain only small envelopes which further de-populates the valley.
This picture is in agreement not only with the position of the radius valley and the rocky nature of the Super-Earths but also with the lack of He escape detection in some sub-Neptunes and the observed spectroscopic water features in other puffed-up planets.

References

Fulton, B. J. and Petigura, E. A. (2018) The Astronomical Journal 156, 264

Jin, S. and Mordasini, C. (2018) The Astrophysical Journal 853, 163

Emsenhuber, A. et al. (2021) Astronomy & Astrophysics 656, A70

Author(s): Moritz Lietzow, Sebastian Wolf

Abstract:

We investigated the impact of selected cloud condensates in extrasolar planetary atmospheres on the net polarization of scattered stellar radiation. For this purpose, we considered a selection of different cloud condensates that are expected to be present in exoplanetary atmospheres.

We used the three-dimensional Monte Carlo radiative transfer code POLARIS [1], that has been extended for radiative transfer calculations in planetary atmospheres [2]. Subsequently, we calculated and studied the net polarized of scattered radiation as a function of planetary phase angle at optical to near-infrared wavelengths.

We found that most of these cloud condensates, such as chlorides, sulfides, or silicates, are distinguishable from each other due to their unique underlying complex refractive index. In particular, an increase or decrease of the net polarization as a function of wavelength and a change of sign in the polarization at specific wavelengths are important features for characterizing cloud compositions in exoplanetary atmospheres [3].

References

1. Reissl, S., Wolf, S., and Brauer, R. (2016), A&A, 593, A87

2. Lietzow, M., Wolf, S., and Brunngräber, R. (2021), A&A, 645, A146

3. Lietzow, M. and Wolf, S. (2022), A&A, in press, arXiv:2205.04815

Author(s): Laurent Schönau, Tunahan Demirci, Jens Teiser, Tetyana Bila, Kolja Joeris, Florence Chioma Onyeagusi, Niclas Schneider, Miriam Fritscher, Felix Jungmann, Maximilian Kruss, Lars Schmidt and Gerhard Wurm

Abstract:

In the formation of a planetary system, kilometre-sized planetesimals represent an intermediate step in the evolution from micrometre-sized particles into full-grown planets. They might consist of very loosely bound millimetre dust granules [1] and their orbital velocity differs from that of the surrounding gas resulting in a headwind [2]. Since self-gravity of a planetesimal is very small, there is a possibility that it loses mass due to wind erosion. This raises the question at which wind speeds and ambient pressures the planetesimal is stable and at which it is not.

We carried out microgravity experiments on wind erosion in parabolic flights (A310 ZERO-G by Novespace) using a wind tunnel setup that can generate a laminar wind profile over a sample bed at low pressures down to 1 Pa. This setup has already been used with glass spheres as sample [3] but this time, a more realistic approach was applied with millimetre-sized SiO2 dust aggregates. The aggregates were produced in an analogous way as dust aggregates at the bouncing barrier in protoplanetary disks might form, i.e. by collisions of micrometre-sized particles, sticking and growing up to the bouncing size.

Wind erosion was observed at an ambient pressure that was an order of magnitude lower than before. Furthermore, by accurately measuring the residual gravity during the microgravity phases, it was possible to determine an angle of repose under the given conditions. Here we report the latest results of the parabolic flight campaigns.

Applied to planet formation, our results support and expand earlier findings that wind erosion might generate forbidden zones for pebble pile planetesimals, i.e. closer to the star [3,4] and wind erosion might filter out eccentric orbits [5].

References

1. Wahlberg Jansson K., Johansen A., Bukhari Syed M., Blum J., (2017), ApJ, 835, 109
2. Weidenschilling S. J., (1977), MNRAS, 180, 57
3. Demirci T., Schneider N., Steinpilz T., Bogdan T., Teiser J., Wurm G., (2020), MNRAS, 493, 5456-5463
4. Rozner M., Grishin E., Perets H. B., (2020), MNRAS, 496. 4827-4835
5. Cedenblad L., Schaffer N., Johansen A., Mehlig B., Mitra D., (2021), ApJ, 921, 123

Author(s): Lena Noack and Caroline Brachmann

Abstract:

Accurate measurements of a planet’s mass, radius and age (provided for example by the PLATO mission and follow-up measurements) together with compositional constraints from the stellar spectrum can help us to deduce potential evolutionary pathways that rocky planets can evolve along, and allow us to predict the range of likely atmospheric properties that can then be compared to observations (from ground or space, i.e. with JWST or in the more distant future with direct imaging such as proposed by the LIFE initiative).

However, for the evolution of composition and mass of an atmosphere, a large degeneracy exists due to several planetary and exterior factors and processes, making it very difficult to link the interior (and hence outgassing processes) of a planet to its atmosphere. The community therefore thrives now to identify the key factors that impact an atmosphere, and that may lead to distinguishable traces in planetary, secondary outgassed atmospheres. Such key factors are for example the planetary mass (impacting atmospheric erosion processes) or surface temperature (impacting atmospheric chemistry, weathering and interior-atmosphere interactions).

Here we investigate the signature that a planet evolving into plate tectonics leaves in its atmophere due to its impact on volcanic outgassing fluxes and volatile releases to the atmosphere – leading possibly to distinguishable sets of atmospheric compositions for stagnant-lid planets and plate tectonics planets. These outgassing fluxes further strongly depend on the evolution of the atmosphere, including atmosphere losses to space or by condensation or weathering.

Author(s): Thorsten Kleine, Christoph Burkhardt, Fridolin Spitzer, Alessandro Morbidelli, Gerrit Budde, Jan Render, Thomas Kruijer

Abstract:

Two fundamentally different processes of rocky planet formation exist, but it is debated which one built the terrestrial planets of the solar system. They formed either by collisions among planetary embryos from the inner solar system or by accreting sunward-drifting millimeter-sized “pebbles” from the outer solar system. We show that the isotopic compositions of Earth and Mars are governed by two-component mixing among inner solar system materials, including material unsampled by meteorites. This unsampled material most likely derives from the innermost disk, whereas the contribution of outer solar system material to the terrestrial planets appears to be limited to a few percent by mass. This refutes a pebble accretion origin of the terrestrial planets but is consistent with collisional growth from inner solar system embryos. The low fraction of outer solar system material in Earth and Mars indicates the presence of a persistent dust-drift barrier in the disk, highlighting the specific pathway of rocky planet formation in the solar system.

Author(s): Thomas A. Stuber, Torsten Löhne, Sebastian Wolf

Abstract:

We analyze the potential to infer the presence of an exoplanet via spatially resolved observations of a coexisting debris disk.

Debris disks are circumstellar distributions of dust, continuously replenished by planetesimal collisions. They often exist alongside exoplanets, which influence the dust dynamics via their gravitational potential. Using numerical simulations, we analyze the observable effects on spatial dust grain distributions that are caused by secular perturbations, originating from an exoplanet orbiting either in- (~ 40 AU) or outside (~ 500 AU) a planetesimal belt. Based on the simulated spatial distributions of dust grains we computed spatially resolved maps of surface brightness at wavelengths ranging from the near-infrared up to the millimeter region.
We identified features of the brightness distributions suitable to distinguish between systems with an inner or outer perturber and possibly detectable, especially with a combined observation with JWST/MIRI and ALMA.

We find that thermal dust emission originating from regions inward the parent planetesimal belt is indicative of an outer perturber. Therefore, combining spatially resolved observations of circumstellar dust with an understanding of the dust dynamics allows to infer far-out and intrinsically dark exoplanets that are difficult to infer on with the common planet hunting methods.

Author(s): Jingyi Mah and Bertram Bitsch

Abstract:

Super-Mercuries, rocky exoplanets with bulk iron fraction of more than 60%, appear to be preferentially hosted by metal-rich stars. It is unclear whether the core accretion mechanism is sufficient to build these iron-rich planets, or if giant impacts are necessary. We investigate the probability of forming the observed super-Mercuries in their natal protoplanetary disks by taking into account the stellar abundances (Fe, Mg, Si, S) of their host stars. We simulate the growth of embryos in the inner regions of the disk and compute their iron compositions using a 1D disk model. Our model also includes the evaporation of pebbles at the location of evaporation fronts. Our simulations are able to reproduce the observed iron compositions of the super-Mercuries provided that all the iron in the disk are locked in pure Fe grains. We also find that increasing the stellar Si/Mg ratio results in an increase in the iron content at the iron evaporation front. Our results thus imply that super-Mercuries are more likely to form around stars with Si/Mg > 1, in rough agreement with observational data.

Author(s): L. Nortmann, A. Reiners, A. Hatzes, N. Piskunov, U. Seemann, I. Ribas, P. J. Amado, J. Caballero, and the CARMENES and CRIRES+ consortia

Abstract:

With the arrival of a new generation of high-resolution infrared spectrographs at medium to large scale observatories in the last years ground based exoplanet atmosphere studies have been established as invaluable complements to space based studies. High resolution allows us to disentangle signals from the star and the planet and unambiguously identify the species of the absorber. It furthermore allows to probe wind speeds, thus, opening a window into the dynamics of the atmosphere.
Here we will give an overview over recent results from work done by the CARMENES and CRIRES+ consortia.
CARMENES is covering both the visible as well as the near infrared range from 0.52 to 0.96 µm and from 0.96 to 1.71 µm and has been contributing to the characterization of atmospheres of transiting exoplanets for over four years. We will present the highlights of the survey and some of the recent results obtained.
CRIRES+ is the fully refurbished and greatly enhanced near-infrared CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES). It operates in spectroscopy mode from 0.95 to 5.2 μm (YJHKLM bands) and is taking first observations for the community since fall 2021. The consortium is planning to dedicate 20+ nights for the study of exoplanet atmospheres, aiming at characterizing both transmission as well as emission features. Here we will show first results from our survey.

Author(s): Amith Govind and Susanne Pfalzner

Abstract:

Recent observations of many protoplanetary discs with spiral arms in young low-mass clusters have challenged theoretical models. A pattern analysis of some spiral arms indicate close flybys as the most probable cause. Hence this requires a rethink of the influence of flybys on protoplanetary discs in low-mass clusters. In this work we study the impact of flybys on protoplanetary discs in young low mass clusters, wherein we built on the observational fact that in the solar neighbourhood, low-mass clusters have a smaller extent than high-mass clusters. Hence, low-mass clusters can have mean and central density comparable to high-mass clusters. We use NBODY6++ to perform simulations of stellar dynamics using the observed cluster mass-radius relations. We find that low-mass clusters can affect disc sizes just as much as, if not more than, high-mass clusters. We even find a significant fraction of small discs (< 10 au) in low-mass clusters. The primary conclusion of this study is that close flybys cannot be neglected in low-mass clusters. We also provide few testable predictions, one of them being that 10%–15% of discs in low-mass clusters will be truncated by flybys to less than 30 au with a sharp outer edge.

References

Pfalzner, S. and Govind, A. (2021) The Astrophysical Journal, Volume 921, Issue 1, id.90, 13 pp.

Exoplanet research has demonstrated a plethora of different kinds of worlds and one of the major questions is, are they inhabited and, if so, can we detect traces of life?

The origin of life on Earth is still not well understood, neither in terms of prebiotic chemistry nor with respect to location. While hydrothermal environments are the favoured environment, different hypotheses lean towards subaerial or subaqueous locations, the first precluding the emergence of life on purely ocean planets. However, we should also consider the possibility that, if life emerged in one type of location on Earth, it may originate in other environments elsewhere. On the other hand, significant evolution of life appears to require abundant water: the lack of permanently available water on Mars will have inhibited evolution beyond a simple, anoxic, prokaryote-like life form. Furthermore, as we understand the evolution of larger, more sophisticated life forms, the presence of oxygen is essential; on Earth produced by a permutation of anoxygenic photosynthesis into oxygenic photosynthesis.

If life is the cosmic phenomenon described by the Chemistry Nobel Prize winner Christian de Duve, the simplest forms of life, similar to terrestrial anaerobic chemotrophs (organisms obtaining their energy from oxidation of organic or inorganic substrates) will be most widespread. However, they do not produce biosignatures that are detectable remotely. Detection of life on exoplanets therefore relies on a planet upon which life has evolved to a stage whereby a biogas, such as oxygen, is produced.

Author(s): Jeanne Davoult, Lokesh Mishra, Yann Alibert

Abstract:

Context: The detection of Earth-like planets is both one of the major goals of planetology and at the same time one of the most complicated. Earth-like planets are difficult to detect and imply a lot of observation time with the current detection methods. Currently only 0.06% of the confirmed exoplanets are similar to Earth by their masses and semi-major axis.

Aims: Here, a way to identify systems, which are likely to harbor an Earth-like planet, is considered. This can facilitate the selection of targets and reduce the time necessary for observations.

Methods: Mishra et. al 2022 (to be submitted) have developed a method for classifying planetary systems according to their architecture. Applied on generation III Bern model synthetic population, a class has been identified in which a majority of systems harbors an Earth-like planet. Using the same classification scheme now taking into account the observational bias, we investigate whether the observed class of a system (the one obtained only from observable planets) could help to find systems more likely to have an Earth-like planet.

Results: The classes in themselves with only the detectable planets are not sufficient to identify systems with an Earth-like planet, but the characteristics of the remaining planets and the prognostic of the intrinsic architecture is a solid base for such a conjecture

References

[1] Mishra L. et al. (2022) To be submitted.

[2] Davoult J. In prep..

Author(s): Anina Timmermann, Yutong Shan, Ansgar Reiners, Andreas Pack

Abstract:

The formation and main element composition of rocky planets can be simulated as equilibrium condensation of the most common species in a protoplanetary disk with parameterized abundance patterns. We have developed an open access python code to perform condensation simulations based on a Gibbs free energy minimisation including thermochemical and stellar abundance databases. Our main objective was to provide a code that is easy to use, adapt, and expand. With our code, we simulated condensation for a representative selection of F, G and K stars. We analysed the influence of stellar abundance patterns and specific element ratios on the equilibrium chemistry in the protoplanetary disk. I will present our results about the connection between stellar elemental abundance patterns, volatility of elements, and planet composition. We found significant variations in condensation temperatures and planetary bulk compositions even for the conservative parameter range of 0.1 < C/O < 0.8, challenging previous assumptions regarding the general consistency of disk chemistry in low to medium C-systems. Our simulations show that the combined differences in various element ratios and overall metallicity of the system have an intricate effect on the condensation behaviour of solid phases. We systematise these effects in an effort to enable cursory estimations of planetary compositions.

Author(s): Matteo Pinamonti, Domenico Barbato, Nicola Nari, Alessandro Ruggieri, Alessandro Sozzetti, Silvano Desidera

Abstract:

The relationships between inner and outer planets plays a key role in unveiling the mechanisms that govern formation and evolution of planetary systems. For this reason, it is important to probe the inner region of systems hosting long-period giants, in search for undetected lower-mass planetary companions: some models suggest that Jupiter-like planets prevent the formation of inner super Earths, while others make the opposite prediction of a direct correlation between the two populations of planets. Moreover, formation mechanisms are strongly dependent on stellar mass, and thus the comparison between different samples of stars provides invaluable insights into these mechanisms.

In this framework, taking advantage of high-resolution echelle spectroscopy from HARPS-N@TNG, we present the high-cadence and high-precision Radial Velocity (RV) monitoring of stellar hosts to long-period giants with well-measured orbits, in search for short-period low-mass planets. We observed a sample of 4 M dwarfs over the last 4 years, and detected of two close-in low-mass planets. Taking advantage of Bayesian statistics to estimate the detection limits of the survey, we measure a higher Super-Earth frequency in the observed Cold-Jupiter sample, with respect to the observed frequencies for field M dwarfs. We then compare these results with a previous observed sample of 17 Solar-type stars, also observed with HARPS-N@TNG, and homogeneously analysed, and we highlight a very different behaviour between G- and M-dwarfs: in the G-sample, the frequency of Super-Earths appears to be diminished, in contrast to what observed for M dwarfs. The results of these surveys provide an important advancement in discriminating between proposed outcomes of different processes for the formation of super Earths in the presence of outer giant companions, and produce the first direct observation of a different influence of Cold Jupiters in the formation of planetary systems around stars of different masses.

Author(s): Dane Späth and Sabine Reffert

Abstract:

To date, around 130 evolved stars are known to host planetary companions. In contrast to their main-sequence counterparts these evolved systems probe a different stellar mass regime and allow to investigate the influence of stellar evolution on planetary systems. Recently however, the existence of several of these planets has been called into question as more data and additional spectral diagnostics became available. One alternative solution to the observed periodic radial velocity variations are intrinsic non-radial oscillations, however it remains unclear how to unambiguously differentiate between planets and oscillations in RV data. I present simulations of the effect of non-radial oscillations on high-resolution spectra showing that the widely used activity indicators can be useful diagnostic tools. I compare first results to HARPS data of a known false positive and to CARMENES spectra acquired for 20 giant stars, which were found to have periodic RV variations with yet unknown origin in a long-term RV survey carried out at Lick observatory.

Author(s): Ana-Catalina Plesa

Abstract:

Over the past decades, large-scale numerical simulations of interior evolution have grown to become one of the most powerful approaches to model the interior of planetary bodies in our Solar System and beyond. Geodynamic models are used to investigate the evolution and distribution of the interior temperature that ultimately affects the distribution of seismic velocities, surface heat flow, and partial melting of the mantle. Combined with constraints derived from planetary mission data and laboratory experiments, these models help us to improve our understanding of the history and present-day thermal state of planetary interiors.

In this presentation, I will focus on the thermal history of Mars and Venus. Results from numerical thermal evolution models will be compared with geophysical and geological data sets in order to provide constraints for the thermal evolution and present-day state of the interiors of Mars and Venus. I will discuss the thermal evolution models of Mars in the context of the most recent data from the InSight mission [1] about the crustal thickness [2], upper mantle structure [3], and martian core size [4]. Predictions from the thermal evolution models of the interior of Venus can be tested by the future Venus missions VERITAS [5] and EnVision [6] that aim to constrain the thermal history and present day volcanic and tectonic activity of Earth’s nearest planetary neighbor.

Acknowledgements:

Numerical simulations were performed on the HoreKa supercomputer funded by the Ministry of Science, Research and the Arts Baden-Württemberg and by the Federal Ministry of Education and Research. A.-C.P. gratefully acknowledges the financial support and endorsement from the DLR Management Board Young Research Group Leader Program and the Executive Board Member for Space Research and Technology.

References

[1] Banerdt, W. B. et al. (2020). Nature Geoscience, 13(3), 183-189.
[2] Knapmeyer-Endrun, B. et al. (2021). Science, 373(6553), 438-443.
[3] Khan, A. et al. (2021). Science, 373(6553), 434-438.
[4] Stähler, S. C. et al. (2021). Science, 373(6553), 443-448.
[5] Smrekar, S. E. et al. (2020). EPSC 2020, Abstract #447.
[6] Ghail, R. et al. (2020). EPSC 2020, Abstract #599.

Author(s): Kai Wu, M.B.N. Kouwenhoven, Rainer Spurzem

Abstract:

Observations of planetary debris disks suggest a strong correlation between the orbits of planets and the orbits of nearby planetary debris particles (PDPs), such as, asteroids, comets and planetesimals. The surrounding stellar population may also play a role, given that most stars and planetary systems are born in dense stellar environments. To determine the effect of planetary companions and the neighboring stellar population on the dynamics of PDPs, we perform direct N-body simulations of star clusters with half-mass radii of 0.77 pc and populations ranging from 8k to 64k stars using NBODY6++GPU. We study the effect of the presence of „50 AU Jupiters“ on massless PDPs that initially have semi-major axes between 20 and 2000 AU around solar-mass stars using REBOUND. When the planet is absent, we obtain an empirical formula for the PDP retention rate as a function of initial semi-major axis, stellar density, and time. In a star cluster environment, the planet does not only rapidly expel most of the PDPs with semi-major axes between 40 and 60 AU, but also significantly affects the PDPs on the MMR orbits. This increases the escape fraction and survivors’ eccentricity. The effect of the planet on the evolution of the population of PDPs statistically decreases with increasing cluster density, because the increased frequency of close encounters dominates the escape, while the planet is also frequently expelled from the planetary system. For clusters of 8k, 10k and 16k, the moment of maximum difference occurs at ~64 Myr, while for 32k and 64k it occurs at ~16 Myr. Among the PDPs escaping from the planetary system, 60.5%-91.5% ends up bound to the cluster. Since the presence of the planet significantly affects the dynamical properties of PDPs that orbit planet-hosting stars, it is possible to find hints of exoplanets by observing debris disks in the cluster. The findings on escaped PDPs can further support the study of the dynamics of free-floating debris in star clusters.

References

Cai M. X., Kouwenhoven M. B. N., Portegies Zwart S. F., Spurzem R., 2017, MNRAS, 470, 4337

Flammini Dotti F., Kouwenhoven M. B. N., Cai M. X., Spurzem R., 2019, MNRAS, 489, 2280

Hughes A. M., Duchêne G., Matthews B. C., 2018, ARA&A, 56, 541

Rein H., Liu S. F., 2012, A&A, 537, A128

Stock K., Cai M. X., Spurzem R., Kouwenhoven M. B. N., Portegies Zwart S., 2020, MNRAS, 497, 1807

Wang L., Spurzem R., Aarseth S., Nitadori K., Berczik P., Kouwenhoven M. B. N., Naab T., 2015b, MNRAS, 450, 4070

Author(s): Ádám Boldog, Vera Dobos, Marijn van der Perk, Amy C. Barr

Abstract:

We investigated rocky exoplanets in the habitable zone of their stars to assess their habitability by determining whether liquid water could be present beneath ice-covered surfaces. We modelled the interior of 27 habitable zone rocky exoplanets assuming four different layers – an iron core, a rock mantle, a high pressure ice layer and a surface ice/water layer. We determined the possible range of water mass fraction in each planet as well as the tidal heating and radiogenic heating. By calculating the total internal heat flux, we estimated the phase state in which H2O is present below the surface. We identified planets which have the highest probability for having internal liquid oceans. These planets could be similar to Europa and Enceladus in our Solar System as their oceans are heated via internal processes. Here the underlying rock can interact with the water through hydrothermal vents which can be favourable for the appearance of simple life forms.

Acknowledgements:

The COFUND project oLife has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 847675.

Author(s): Giovanni Picogna, Barbara Ercolano, Kristina Monsch, Jeremy J. Drake, Thomas Preibisch and Catherine C. Espaillat

Abstract:

The strong X-ray irradiation from young solar-type stars may play a crucial role in the thermodynamics and chemistry of circumstellar discs, driving their evolution in the last stages of disc dispersal as well as shaping the atmospheres of newborn planets. We study the influence of stellar mass and spectral hardness on circumstellar disc mass-loss rates due to X-ray irradiation, adopting spectra based on spectral parameters derived from the observations of young stars in the Orion nebula cluster from the Chandra Orion Ultradeep Project (COUP). We focus on stars with masses between 0.1 and 1 solar mass, which are the main target of current and future missions to find potentially habitable planets. We find that disc wind mass loss rates are controlled by the stellar luminosity in the soft (100 eV to 1 keV) X-ray band, and that there is a linear relationship between the mass-loss rates and the stellar masses when changing the X-ray luminosity accordingly. We provide new analytical relations for the mass-loss rates and profiles of photoevaporative winds as a function of the stellar mass and X-ray spectra that can be used in disc and planet population synthesis models. Our photoevaporative models correctly predict the observed trend of inner-disc lifetime as a function of stellar mass with an increased steepness for stars smaller than 0.3 solar masses, indicating that X-ray photoevaporation is a good candidate to explain the observed disc dispersal process.

Acknowledgements:

The COFUND project oLife has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 847675.

Author(s): Konstantin Herbst, Andreas Bartenschlager, J. Lee Grenfell, Miriam Sinnhuber, Fabian Wunderlich

Abstract:

Exoplanets are as diverse as they are fascinating. They vary from ultrahot Jupiter-like low-density planets to presumed gas-ice-rock mixture worlds such as GJ 1214b or worlds such as LHS 1140b, which feature twice the Earth’s bulk density. Regarding the great diversity of exoplanetary atmospheres, much remains to be explored. For a few selected objects, such as GJ1214b, Proxima Centauri b, and the TRAPPIST-1 planets, the first observations of their atmospheres have already been achieved or are expected soon with the launch of the James Webb Space Telescope envisaged in October 2021. However, to interpret these observations, model studies of planetary atmospheres that account for various processes — such as atmospheric escape, outgassing, climate, photochemistry, as well as the physics of air showers and the transport of stellar energetic particles and galactic cosmic rays through the stellar astrospheres and planetary magnetic fields — are necessary. Here, we present our model suite INCREASE, a planned extension of the model suite discussed in Herbst et al. (2019).

References

Herbst, K., Grenfell, J., Sinnhuber, M., et al. 2019, Astron. Astrophys., 631, A101.

Author(s): Tim D. Pearce

Abstract:

We know little about the outermost planets in exoplanetary systems, because current detection techniques are insensitive to moderate-mass planets on wide orbits. However, insight can be gained by using debris discs (extrasolar equivalents of our Asteroid and Kuiper Belts) as indirect probes of planetary systems. This approach has been widely applied over the past few decades, allowing us to infer the presence and properties of unseen planets from their gravitational influence on observed debris. Now, with the advent of modern equipment such as JWST, we are finally approaching the era where direct detections of these long-predicted planets should be possible. In this talk I review the rich and exciting field of planet-debris interactions, outlining its historical evolution, the diverse techniques for constraining planets from debris, and how it is likely to develop in future. I discuss what the approach teaches us about planet populations, debris discs, and planet formation and evolution mechanisms, as well as the insights that we would gain from future detections (or non-detections) of expected planets. The talk should be accessible to those without detailed knowledge of planetary system dynamics or debris-evolution mechanisms; instead I aim to summarise what we can infer about planets from debris observations, as well as the strengths and limitations of this approach.

Author(s): Ema Valente and Alexandre Correia

Abstract:

Close-in planets undergo strong tidal interactions with the parent star that modify their spins and orbits. It is commonly assumed that the rotation of this planets is synchronous and the planet spin axis is aligned with the normal to the orbit (zero planet obliquity). Here we show that, for non-zero eccentricities, the rotation rate can be trapped in spin–orbit resonances that delay the evolution towards the synchronous state. More interestingly, we observe that capture in some spin–orbit resonances may also excite the obliquity to high values rather than damp it to zero. Depending on the system parameters, obliquities up to 80 degrees can be maintained throughout the entire lifetime of the planet. This unexpected behaviour is particularly important for Earth-like planets in the habitable zone of M-dwarf stars, as it may help to sustain temperate environments and thus more favourable conditions for life.

Author(s): Steven Rendon Restrepo and Pierre Barge

Abstract:

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]. Self-gravity (SG) plays a key role in this scenario, particularly when high dust density clumps are trapped in the vortex core.

In the case of 2D bi-fluid simulations, we demonstrate that SG needs to be estimated four times, instead of one, in order to correctly account for dust contribution. This requires introducing a gas-dust smoothing length which could be key for an eventual gravitational collapse and/or gaseous envelope capture. We propose to show our early results on this problem, which was addressed using high-resolution, bi-fluid simulations in a thin disc (2D) thanks to the new RoSSBi3D [6] code.

References:

[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] Tanga, P., Babiano, A., Dubrulle, B., & Provenzale, A. 1996, Icarus, 121, 158
[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
[6] Rendon Restrepo, S., Barge, P., and Vavrik, R., “RoSSBi3D: a 3D and bi-fluid code for protoplanetary discs”, submitted to A&A (2022)

Author(s): Gayathri Viswanath, Markus Janson, Carl-Henrik Dahlqvist, Dominique Petit dit de la Roche, Matthias Samland, Julien Girard, Prashant Pathak, Markus Kasper, Fabo Feng, Michael Meyer, Anna Boehle, Sascha P. Quanz, Hugh R. A. Jones, Olivier Absil, Wolfgang Brandner, Anna-Lise Maire, Ralf Siebenmorgen, Michael Sterzik, Eric Pantin

Abstract:

Developments in theoretical knowledge as well as instrumentation have, in the past decade, pushed the boundaries of what high-contrast imaging can achieve, both in terms of detection sensitivity and constraining planet properties. Direct imaging surveys in the near-infrared (NIR) and longward wavelengths have proven particularly useful in detecting younger giant planets at wide orbital separations. The scientific work outlined in this talk is one such result of an imaging pursuit of a young giant planet which has long eluded NIR imaging surveys in the past, yet revealing its existence via radial velocity trends and astrometry of its Sun-like, parent star, epsilon Ind A, which is near enough to be visible to the naked eye in the night sky. I present results from its observations using both the NaCo (L’) and NEAR (10–12.5 microns) instruments at VLT, derive brightness limits from the non-detection of the companion with both instruments, and interpret the corresponding sensitivity in mass based on both cloudy and cloud-free atmospheric and evolutionary models. We arrive at unprecedented sensitivities close to the bright star (200-300 K) and constrain the age of the system to atleast 2 Gyr from our analysis. NaCo offers the highest sensitivity to the planetary companion but the combination with NEAR wavelength range adds a considerable degree of robustness against uncertainties in the atmospheric models. This underlines the benefits of including a broad set of wavelengths for the detection and characterisation of exoplanets in direct imaging studies. The new constraints for epsilon Indi Ab derived in this work set a firm foundation for further MIR imaging surveys for the planet, especially with upcoming more sensitive, advanced instruments in the latter half of the decade, giving hope for a possible detection of this elusive giant in the near future.

Author(s): Dominik C. Hezel

Abstract:

The past years have seen various and significant efforts to make cosmochemical data FAIR (Findable, Accessible, Interoperable, Reproducible). The MetBase database has been founded almost 30 years ago, but we only recently could transformed it to a paywall-free database. Last year, the NFDI4Earth (nfdi4earth.de) consortium started as part of the national research data infrastructure (nfdi.de), an almost 1 billion Euro initiative. At the GU Frankfurt, we are Co-Spokesperson of the NFDI4Earth. The NFDI4Earth seeks to build an infrastructure to connect Earth System Science (ESS) databases and repositories, accessible via a single OneStop4All. Cosmochemical databases are regarded as part of ESS, and access to cosmochemical databases will be integrated into the NFDI4Earth. In a pilot project within the NFDI4Earth, we currently align the database schema of MetBase with NASA’s Astromaterials database, and build a Web-Interface for quick data-access, -visualisation, -modelling, and -download. The starting point will be the existing, comprehensive MetBase web-interface. Together with our colleagues from Astromaterials, we are also in the process to merge MetBase and Astromaterials into one single database. Desperately required standards and metadata for cosmochemical data are planned to be provided – although not necessarily developed – by the just started, global OneGeochemistry initiative, which is part of the EU funded WorldFAIR project. The OneGeochemistry initiative includes cosmochemistry and is led by e.g., our colleagues from Astromaterials, as well as us.

I will present a short overview of these efforts and initiatives. More importantly, I will use two examples to illustrate the potential of cosmochemical data science. In these, I will show that chondrules as well as chondrules and matrix were not formed independently at different locations in the protoplanetary disk and later mixed together, but rather locally from the same reservoir.

Author(s): Anne-Sophie Libert

Abstract:

The diversity of the hundreds of discovered extrasolar systems puzzles our understanding of the formation and long-term evolution of planetary systems. The detected planetary systems generally suffer from large observational uncertainties. In this talk, I will discuss recent results showing how dynamical studies can be useful to constrain the orbital parameters of tightly packed planetary systems which harbor two-body resonances and/or chains of resonances involving three or more planets. More precisely, I will show how i) periodic orbits can serve as dynamical clues to validate the parametrization of detected systems, ii) TTVs keep track of the migration history of planetary systems, and iii) TTVs provide signatures of three-body resonances accessible by future monitoring of the systems. Applications to K2-21, K2-24, Kepler-9, Kepler-108, and TRAPPIST-1 will be discussed. This talk aims at illustrating how the interplay between formation, dynamics, and stability can contribute to bridge the gap between observations and theoretical studies.

Joint work with E. Agol, K.I. Antoniadou, and J. Teyssandier.

Author(s): Henrik Knierim, Sho Shibata, Ravit Helled

Abstract:

The origin of giant exoplanets on short-period orbits is a key open question in planetary science. Measurements of the atmospheric composition of these planets can reveal crucial information on the planetary origin. In this talk, I will show that the two leading formation scenarios for hot/warm Jupiters: formation in the outer disk followed by migration and in-situ formation, lead to significant differences in the predicted atmospheric composition. We use N-body simulations of planetesimal accretion for various planetary formation locations, planetary masses, as well as planetesimal sizes, and estimate the accreted heavy-element mass and final planetary composition for these two formation models. We show that migrating giant planets are much more metal-rich than giant planets that form in-situ. The refractory-to-volatile ratio is above one for migrating planets but below 0.4 for planets that form in-situ. We also identify very different trends between heavy-element enrichment and planetary mass for these two formation mechanisms. Our study highlights the importance of measuring the atmospheric composition of warm Jupiters and its potential to reveal the planetary origin.

Author(s): Enric Palle and Rafa luque

Abstract:

Planets smaller than Neptune are ubiquitous in the Galaxy and those around M stars constitute the bulk of warm and temperate worlds amenable for detailed atmospheric characterization. In this talk, we present a re-analysis of all the available data on small transiting planets around M dwarfs, refining their masses and radii (Luque & Pallé 2022, in press). Our precisely characterized sample reveals that this population is well described by only three discrete planet density populations, with bulk densities centered at 1.0, 0.5 and 0.24 relatively to Earth’s. The first are rocky planets, the second are water worlds, and the third are puffy planets with Neptune-like densities. This density classification offers a much better insight to disentangle planet formation and evolution mechanisms, which are degenerate when using a radius-based classification. Our results are at odds with atmospheric mass-loss models aiming to explain the bimodal radius distribution and suggest that the gap separates dry from water worlds rather than rocky planets with or without H/He envelopes. Formation models including type I migration explain naturally the observations independently of the accretion mechanism: rocky planets form within the snow line, water worlds form beyond and later migrate inwards.

Author(s): Zijia Cui, John C. B. Papaloizou, Ewa Szuszkiewicz

Abstract:

In this presentation I will discuss an occurence of a robust repulsion mechanism [1] between two low-mass planets migrating in a gaseous protoplanetary disk. This mechanism invokes density waves emitted by one planet transferring angular momentum to the coorbital region of the other and then directly to it through the horseshoe drag. We formulate simple analytical estimates, which indicate when the repulsion mechanism is effective. One condition for a planet to be repelled is that it forms a partial gap in the disk and another is that this should contain enough material to support angular momentum exchange with it. Using two-dimensional hydrodynamical simulations, we obtain divergent migration of two super-Earths embedded in a protoplanetary disk because of repulsion between them and verify these conditions. In our study we focus on the systems containing the super-Earths, because they are the most numerous planets known till now. To investigate the importance of resonant interaction, we study the migration of planet pairs near first-order commensurabilities. It appears that proximity to resonance is significant but not essential. In this context we find repulsion still occurs when the gravitational interaction between the planets is removed, suggesting the importance of angular momentum transfer through waves excited by another planet. This may occur through the scattering of coorbital material (the horseshoe drag), or material orbiting close by. Our results indicate that if conditions favor the repulsion between two planets described above, we expect to observe planet pairs with their period ratios greater, often only slightly greater, than resonant values or possibly rarity of commensurability.

References

Cui, Z., Papaloizou, J. C. B., & Szuszkiewicz, E. 2021, ApJ, 921, 142

Author(s): Engin Keles

Abstract:

The comparison of exoplanets with well-studied Solar System planets can provide answers to the fundamental questions regarding their evolutionary path. The study of exoplanet atmospheres via high-resolution transmission spectroscopy has shown great success, especially for Jupiter-type planets. In the last years, this study also continued with promising investigations towards the atmospheric characterization of terrestrial exoplanets. One possible target for such investigation is the super Earth-sized exoplanet 55 Cnc e, which is one of the most studied terrestrial exoplanets to date. Currently, there are two possible atmospheric scenarios for 55 Cnc e: Either there is a heavy-weighted envelope or there is no gaseous envelope at all i.e. a rocky surface similar to Mercury, of our Solar System. Here, we present high-resolution (R = 120 000) transit observation of this planet, acquired with the PEPSI instrument at the Large Binocular Telescope, aiming to search for absorption signatures from various species in the puzzling atmosphere of 55 CNC e.

References

Keles et al. (2022), MNRAS, 513, 1544

Author(s): Kevin Heng, Brett Morris, Daniel Kitzmann, Liming Li

Abstract:

The albedo of a celestial body is the fraction of incident starlight reflected by it. The study of the albedos of Solar System objects is at least a century old, at least in the Western world. As examples: Bond (1861) speculated on the near-unity albedo of Jupiter, while Russell (1916) observed the opposition surge of the Moon near and at full phase. The light of a planet or moon varying with orbital phase is known as its phase curve. Modern astronomical facilities have enabled the measurement of phase curves of reflected light and thermal emission from exoplanets (e.g. Kepler, TESS, CHEOPS, Hubble, Spitzer), which enables the investigation of atmospheric dynamics and aerosols. I will concisely review and discuss historically important work, including seminal contributions by Lommel (1887), Seeliger (1888), Chandrasekhar (1960), Sobolev (1975) and Hapke (1981). These introductions set the stage for a detailed discussion of our recent work on generalising these classic works to derive closed-form, ab initio solutions for the geometric albedo and reflected light phase curve. This novel theoretical framework is applied to Kepler space telescope data of the hot Jupiter Kepler-7b, where we demonstrate that one may infer fundamental aerosol (single-scattering albedo, scattering asymmetry factor) and atmospheric (geometric albedo, Bond albedo, phase integral) properties from precise photometry alone, thus providing powerful complementary information to spectra. Another case study are the Cassini phase curves of Jupiter, which were measured in the early 2000s by the Cassini space mission but never subjected to Bayesian inference.  By inverting the Cassini phase curves, we infer that aerosols in the Jovian atmosphere are large, irregular, polydisperse particles that may be responsible for causing coherent backscattering of sunlight. I end by discussing the implications for interpreting data from the James Webb Space Telescope.

References

Heng, K., and Li, L. (2021), Astrophysical Journal Letters, 909, L20

Heng, K., Morris, B.M., and Kitzmann, D. (2021), Nature Astronomy, 5, 1001

Author(s): Tabea Bogdan, Cynthia Pillich, Joachim Landers, Heiko Wende, Gerhard Wurm

Abstract:

In the early phases of planet formation in the protoplanetary disc, grains drift towards the star experiencing ever higher temperatures. The sticking properties play an important role when it comes to dust aggregation. Tensile strength measurements by means of the Brazilian test along with results from Mössbauer spectroscopy suggest that there is a spacial region that favours planetesimal formation between 900 K and 1300 K [1,2].

For the Brazilian test pieces of two meteorites, namely Sayh al Uhaymir 001 and Allende, were milled to micrometer dust, pressed into cylinders, and tempered at increasing temperatures up to 1400 K before the tensile strength measurement. Comparing sticking properties in terms of surface energies in relation to the heating temperature of the two different meteorite samples, they show no significant difference for heating under vacuum. Both datasets show a considerable increase in sticking around 1200 K by orders of magnitude.

Since gaseous hydrogen is the most abundant element in protoplanetary discs, we followed the same measurement procedure but tempering in a continuous hydrogen atmosphere. The heating chamber is flushed with hydrogen during the entire heating process. The relative surface energies still increase monotonously and rise by orders of magnitude around 1200 K.

We see an influence of composition and atmosphere as well as water content, grain size and morphology on sticking properties. Overall, also our new results not only suggest subtle changes but imply a boost in surface energy for high-temperature dust. This continues to support the idea of a hot spot around 1200 K that favours aggregation and might trigger a high number of planetesimals and subsequently  planets in the inner part of protoplanetary discs [in prep].

References

[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. A&A, 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. A&A, 652, A106.

Author(s): Hendrik Schmerling, Elisa Goffo, Davide Gandolfi, Martin Pätzold, Sascha Grziwa, Carina Person, et al.

Abstract:

The Transiting Exoplanet Survey Satellite (TESS) has revealed a plethora of new and exiting planet candidates via transit observation. Despite this feat, those data are usually on its own not sufficient enough to confirm that those candidates are in fact planets. This lead to the often used method of follow up RV confirmation. Measuring the orbital and planetary parameters is important to complete our picture of planetary formation and evolution since only solid statistics as well as interesting case studies of planets can help us gain important insights into the nature of planets lives and that of their host stars.
We observed the late K dwarf CD-31 1415 with RV measurements to constrain the mass and density of the planet corresponding to TOI 2427 as well as investigate the presence of further companions to the host star
Here we use the TESS transit data as well as Radial Velocity (RV) measurements taken by HARPS as well other observational data north to solidify the detection of the transiting planet TESS Object of Interest (TOI) 2427b as well as reveal another, non-transiting companion to its host star CD-31 1415.

Author(s): Susanne Pfalzner, Shahrzad Dehghani, Arnaud Michel, Amith Govind

Abstract:

The lifetime of protoplanetary discs is a key parameter for the formation of planets. Observations of disc fractions in star clusters imply median disc lifetimes of only 1 — 3 Myr. Individual lifetimes vary from <1 Myr to well over 20 Myr. Current disc lifetime determination is dominated by data from clusters younger than 4 Myr. However, there are some clusters older than 8 Myr with known disc fractions. We find that giving these older clusters equal rating, much longer median disc lifetimes of 5 — 10 Myr emerge. We show that the discrepancy between the derived median disc lifetimes is likely connected to the fact that many young clusters are located at larger distances. High-mass stars have shorter disc lifetimes than low-mass stars. Thus young distant clusters suffer from the problem of limiting magnitudes and bias towards more luminous stars. We find that proceeding from the median disc lifetimes to their actual distribution is the essential next step. For a Gaussian-shaped distribution, we find that median disc lifetimes of 7 — 8 Myr and an initial disc fraction of 80\% give the best fit to the observational data. For high-mass stars (B — K 5.5) this reduces to a median of approximately 4 Myr. Two new challenges emerge: (1) How and why high-mass stars can form planets much faster and (2) what is the reason for the width in disc lifetimes in low-mass stars. We demonstrate that the large spread in disc lifetimes might be the key to explaining the diversity of planets and planetary systems.

Author(s): Tim Lichtenberg and Matthew S. Clement

Abstract:

Ocean-vaporising impacts of chemically reduced planetesimals onto the early Earth have been suggested to catalyse atmospheric production of reduced nitrogen compounds and trigger prebiotic synthesis despite an oxidized lithosphere. While in the Solar System geochemical evidence supports a dry, highly reduced late veneer, the composition of late-impacting debris around lower-mass stars is uncertain due to variable volatile loss from protoplanets during the extended pre-main sequence phase of M-dwarfs. We perform simulations of late-stage planet formation across the M-dwarf mass spectrum to derive upper limits on reducing bombardment epochs in Hadean analog environments. We contrast the Solar System scenario with varying initial volatile distributions due to extended primordial runaway greenhouse phases on protoplanets or desiccation of smaller planetesimals by internal radiogenic heating. We find a decreasing rate of late-accreting reducing impacts with decreasing stellar mass. Young planets around stars 0.4 solar masses experience no impacts of sufficient mass to generate prebiotically relevant concentrations of reduced atmospheric compounds once their stars have reached the main-sequence. For M-dwarf planets to reach Earth-like concentrations of atmospheric volatiles (and not order of magnitudes more), both planetesimals and larger protoplanets must undergo extensive devolatilization processes. This suggests transiently reducing surface conditions on young rocky exoplanets to be more likely around FGK- than M-dwarfs.

Author(s): Cedric Gillmann

Abstract:

With the deployment of the JWST earlier in 2022 and promises of new insights in the composition of exoplanetary atmospheres in the next years to decades, we turn back to the Earth’s and its neighbors’ fluid envelops for guidance. We will probably never, in the foreseeable future, obtain detailed direct information of exoplanetary composition, dynamics or climate conditions. However, the observation of the present-day Solar System informs us on the mechanisms and processes possibly at work on any terrestrial planet. On the other hand, we only possess a snapshot of the state of a handful of bodies near us: Earth, Venus, Mars, and Mercury (plus a few satellites), which makes more general predictions a long shot. Exoplanets will give us access to a whole population of possible atmosphere, allowing us i) to assess if our Solar System planets are rare or common and ii) to catch a glimpse of a range of possible past states for those atmospheres.

Here, we discuss the similarities and differences between Solar system planetary atmospheres. The main mechanisms that affect their evolution through time are then reviewed, and assessed, discussing the possible causes for their evolutionary divergences and their roles in the overall planetary evolution. The main mechanisms we discuss are based on volatile exchanges: volcanic outgassing, atmospheric escape, and atmosphere/surface reactions. We further discuss how climate is affected by those exchanges and how the atmosphere itself participates into the global planetary evolution. We highlight how those various processes can be affected by the previous history of terrestrial planets. Their effects can themselves widely differ depending on time and planetary characteristics. Interactions between the atmosphere, the surface and interior of the planet, and its stellar environment are considered. We discuss common feedback mechanisms and cycles, possibly affecting planetary atmospheres on the global scale.

Author(s): Alexandre Emsenhuber, Christoph Mordasini, Remo Burn

Abstract:

Planetary population synthesis is a powerful tool to understand the physics of planetary system formation. The goal is to find the model that statistically best reproduces observed exoplanetary systems from the diversity of protoplanetary discs. Here, we use one population computed using the Generation III Bern model [1] to explore how different planetary system architectures emerge and which conditions lead to their formation. We find that systems can be classified into four main architectures: Class I of near-in situ ordered rocky planets, Class II of migrated sub-Neptunes, Class III of mixed low-mass and giant planets, broadly similar to the Solar System, and Class IV of dynamically active giants without inner low-mass planets. These four classes exhibit distinct typical formation pathways and are characterised by certain mass scales. We find that Class I forms from the local accretion of planetesimals followed by a giant phase, and the final planet masses correspond to what is expected from such a scenario, the „Goldreich mass“. Class II, the migrated sub-Neptune systems form when planets reach the `equality mass‘ where accretion and migration timescales are comparable before the dispersal of the gas disc, but not large enough to allow for rapid gas accretion. Giant planets form when the „equality mass“ allows for gas accretion to proceed while the planet are migrating, i.e. when the critical core mass is reached. The main discriminant of the four classes is the initial mass of solid building blocks in the disc, while environmental aspects have secondary, but still discernible effects. The distinction between mixed Class III systems and Class IV dynamically-active giants is in part due to the stochastic nature of dynamical interactions rather than the initial conditions only. For instance, a scattering event between two giants leading to the ejection of one planet is usually sufficient to destabilise the inner, lower-mass planets.

References

1. Emsenhuber, A., et al. A&A 656, A70 (2021) https://doi.org/10.1051/0004-6361/202038863

Author(s): Kristine Lam, Szilárd Csizmadia, et al.

Abstract:

Ultrashort-period (USP) exoplanets have orbital periods shorter than 1 day and they typically have rocky compositions. Precise masses and radii of USP exoplanets could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b (1), using high-precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude of 10.2), nearby, and red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of 0.718 ± 0.054 Earth-radii and a mass of 0.546 ± 0.078 Earth-masses, making it a sub-Earth planet. The corresponding bulk density is 8.106 ± 2.165 grams per cubic centimeter—close to that of iron. An interior structure model predicts that the planet has an iron core radius fraction of 86 ± 5 %, similar to that of Mercury’s interior. In this work, we also discuss the demographics and architectures of USP exoplanets and some implications for their formation and evolution.

References

(1) Lam et al. 2021, Science, 374, 6572, 1271-1275

Author(s): Mohamad Ali-Dib, Andrew Cumming, Doug N. C. Lin

Abstract:

We investigate the origins of cold sub-Saturns (CSS), an exoplanetary population inferred from microlensing surveys. If confirmed, these planets would rebut a theorised gap in planets’ mass distribution between those of Neptune and Jupiter caused by the rapid runaway accretion of super-critical cores. In an attempt to resolve this theoretical-observational disparity, we examine the outcomes of giant collisions between sub-critical protoplanets. Due to the secular interaction among protoplanets, these events may occur in rapidly depleting discs. We show that impactors ∼ 5% the
mass of near-runaway envelopes around massive cores can efficiently remove these
envelopes entirely via a thermally-driven super-Eddington wind emanating from the core itself, in contrast with the stellar Parker winds usually considered. After a brief cooling phase, the merged cores resume accretion. But, the evolution timescale of transitional discs is too brief for the cores to acquire sufficiently massive envelopes to undergo runaway accretion despite their large combined masses. Consequently, these events lead to the emergence of CSS without their transformation into gas giants. We
show that these results are robust for a wide range of disc densities, grain opacities and silicate abundance in the envelope. Our fiducial case reproduces CSS with heavy (≳ 30M⊕) cores and less massive (a few M⊕) sub-critical envelopes.

References

Ali-Dib, Cumming & Lin (2021) MNRAS.

Author(s): Rengel M., Shulyak D., Hartogh P., Sagawa H., Moreno R., Jarchow C., Breitschwerdt D.

Abstract:

Hydrogen cyanide (HCN) may be present in hot super-Earths with nitrogen dominated atmospheres, and may become a primary specie to be searched for in thermal emission. In this contribution we present a HCN vertical distribution reference for modelling the atmospheres of hot super-Earths or Titan-like exoplanets. Our mean HCN vertical profile reference is based on our measurements of HCN in Titan’s stratosphere using ground-based submillimetre observations acquired quasi-simultaneously with the Herschel ones. We applied a line-by-line radiative transfer code to calculate the synthetic spectra of HCN, and a retrieval algorithm to retrieve the HCN vertical distributions.

Our HCN inter-comparisons allowed us also to perform a consistency check between space and ground-based observations, and to obtain a profile that could be assimilated into climate models, chemistry calculations, as a guide to understanding what to expect in an N-dominated atmosphere, and as a reference in preparation for future observations of Titan and Titan-like exoplanets for example.

Author(s): Sofia Savvidou and Bertram Bitsch

Abstract:

The inferred dust masses from Class II protoplanetary disc observations are smaller or equal to the observed exoplanet systems and this has ignited a mass budget problem discussion. Planet formation is directly linked to the birthing environment that protoplanetary discs provide. The disc properties determine if a giant planet forms and how it evolves. We perform numerical simulations of planet formation via pebble and gas accretion, including migration, in a viscously evolving protoplanetary disc, investigating the most favorable conditions for giant planet formation, while tracing the dust mass evolution simultaneously. As expected, the presence of a giant planet in the disc can greatly influence the evolution of the disc itself and prevent rapid dust mass loss by trapping the dust outside its orbit. We find that early planet formation is crucial to forming a giant, along with a high initial disc mass. Larger disc radii ensure a pebble flux for a long time, which is beneficial for growing the cores of giant planets. However, smaller discs with the same mass can allow more efficient gas accretion onto already formed planetary cores, due to the larger amount of available gas, leading to more massive gas giants. Our findings strengthen the hypothesis that planet formation has already happened or is ongoing in Class II discs. Most importantly, we find that the optically thin dust mass significantly underestimates the total dust mass in the presence of a giant planet and could be the answer to the hypothetical mass budget problem.

Author(s): Carolina Villarreal D’Angelo

Abstract:

GJ436b was the first detection of atmospheric escape from a warm-Neptune around an M-dwarf star. The extreme absorption observed in the Lyman-alpha line during transit indicates the existence of a very long tail of planetary neutral material trailing the planet, not being completely swept by the interaction with the stellar wind. As GJ436b lies in the edge of the sub-Jovian desert, the characterisation of the stellar and planetary wind parameters will help to understand the process involved in the erosion of the planetary atmosphere, and will give us a hint on the possibles scenarios that lead to the formation of such desert.

In this talk I will present the results of 3D radiative hydrodynamics simulations of GJ436 planetary system. These simulations take into account the stellar and planetary wind interaction and include the process of radiation pressure and photoionisation. The models explore a small but representative set of values for the EUV flux and stellar wind strength. The simulation outputs show that the observed absorption profiles in Lyman-alpha can be reproduced in a hydrodynamic scenario where the interaction of both winds forms a shock ahead of the planet.  From these outputs, a range of values for the planetary mass loss rate and the stellar wind are extracted by comparing synthetic Lyman-alpha profiles with the observations. Moreover, in order to remove the degeneracy in the best fitting parameters found for this system, synthetic observations of the H-alpha line are created from these models and compared to the observations.

Author(s): Sebastian Markus Stammler, Joanna Drążkowska, Tilman Birnstiel

Abstract:

High-precision isotopic measurements in meteorites reveal a dichotomy indicating that carbonaceous and non-carbonaceous meteorites must have formed in two distinct reservoirs within the protoplanetary disk. These reservoirs must have coexisted spatially separate for several million years (Kruijer et al. 2017). This is often explained by the early formation of Jupiter’s core within one million years, opening a gap in the disk. Inwards drifting dust pebbles are then trapped in the pressure bump at the outer edge of the gap, which is separating the inner disk from the solids in the outer disk. This formation hypothesis, however, neglects the evolution of dust particles trapped in the pressure bump producing small fragments in collisions, which can then be carried across the planetary gap by the gas.

We performed simulations of dust particles in a protoplanetary disk with a gap opened by an early formed Jupiter core including dust growth and fragmentation as well as dust transport using the dust evolution software DustPy (Stammler & Birnstiel 2022). Our results show that the inner disk is contaminated by outer disk material on timescales that is inconsistent with the meteoritic record. Additionally, we performed a suite of simulations with different planet masses and values of the dust diffusivity to further constrain the dust permeability of planetary gaps.

References

1. Kruijer, T. S. et al. 2017, PNAS, 114, 6712
2. Stammler, S. M., & Birnstiel, T. 2022, arXiv e-prints, arXiv:2207.00322

Author(s): Marleau, Aoyama, Mordasini, Kuiper, Follette, Turner, Cugno, Manara, Haffert, Kitzmann, Ringqvist, Wagner, van Boekel, Sallum, Janson, Schmidt, Venuti, Lovis, Mordasini

Abstract:

Accreting planetary-mass objects have been detected at H alpha, but targeted searches have mainly resulted in non-detections. Emission lines should originate from the accretion shock, making them susceptible to extinction by the accreting material. In the near future, high-resolution (R>50,000) spectrographs operating at H alpha should enable the study of how the incoming material shapes the line profile. In this contribution, we report the results from radiative transfer calculations of the H alpha line for three simplified accretion geometries: spherical symmetry, polar inflow, and magnetospheric accretion. We focus on (i) how much the gas and dust accreting onto a planet reduce the line flux from the shock and (ii) how they affect the line shape.
We found that at low accretion rates (Mdot < 3e-6 MJ/yr), gas extinction is essentially negligible and at most a few magnitudes at higher Mdot. For most parameter combinations, extinction by the accreting matter should be negligible, simplifying the interpretation of observations. However, extinction flattens the L_Ha–Mdot relationship, which gets a maximum luminosity L_Ha~1e-4 LSun towards Mdot~1e-4 MJ/yr for a planet mass ~10 MJ. At high Mdot, strong absorption reduces the H alpha flux, and some measurements can be interpreted as two Mdot values. Finally, we show how highly resolved line profiles (R~1e5) can provide (complex) constraints on the thermal and dynamical structure of the accretion flow, helping to reveal by what mechanisms protoplanets accrete.

References

Marleau, G.-D. et al. (2022) A&A 657, 38 (https://ui.adsabs.harvard.edu/abs/2022A&A…657A..38M)

Author(s): René Heller and Michael Hippke

Abstract:

Over 200 moons have been found around the solar system planets and thousands of planets have been found beyond the solar system. But no moon has ever been clearly discovered around an exoplanet. Two main reasons can be cited for this lack of exomoon discoveries. (1) It is unclear if sufficiently large exomoons actually exist in the observationally accessible part of the parameter space. Exomoons as small as even the largest solar system moons (Ganymede and Titan) can only be found in very fortunate circumstances. (2) The modeling of exoplanet-exomoon transits with mutual eclipses and stellar limb darkening is mathematically and computationally demanding.

We present Pandora, the first publicly available (github.com/hippke/Pandora) fully automated photodynamical software to model the combined transits of exoplanets with exomoons including mutual eclipses (Hippke & Heller 2022). We have optimized Pandora for computational speed. On a standard laptop, Pandora can compute about 10^8 models in 5 hours, which is necessary to sample the huge parameter space for possible solutions. Pandora can also generate video animations of the simulated star-planet-moon systems (youtu.be/89lEuPgrl8s).

We present our first application of Pandora to the previously claimed exomoon candidates around the Jupiter-sized exoplanets Kepler-1625b and Kepler-1708b. Statistical evidence for an exomoon around Kepler-1625b is caused entirely by the slight shallowness of one transit observed with the Hubble Space Telescope and by the previously reported timing offset of this Hubble transit. This makes a systematic effect much more likely than an exomoon. For Kepler-1708 b, with only two transits observed by Kepler, we find much lower statistical evidence than previously reported. Our injection-retrieval experiments show that real transits of large exomoons would have much higher evidence than those candidats. We conclude that neither Kepler-1625 b nor Kepler-1708 b are orbited by a large exomoon.

Acknowledgements:
RH acknowledges support from the German Aerospace Agency (Deutsches Zentrum für Luft- und Raumfahrt) under PLATO Data Center grant 50OO1501.

References:

Hippke, M. and Heller, R. (2022) Pandora: A fast open-source exomoon transit detection algorithm. Astronomy & Astrophysics 662, A37, DOI:10.1051/0004-6361/202243129

Author(s): Julia Kobus, Sebastian Wolf, Thorsten Ratzka, Robert Brunngräber

Abstract:

Optical and infrared spatially unresolved multi-epoch observations have revealed the variability of pre-main sequence stars and/or their environment. Moreover, structures in orbital motion around the central star, resulting from planet-disk interaction, are predicted to cause temporal variations in the brightness distributions of protoplanetary disks. Long-baseline interferometry provides the opportunity to observe the temporal variability of these structures and thus to study time-dependent phenomena of the planet formation process on scales of ~1 au – corresponding to timescales of months to years – in nearby star-forming regions.

We make use of this opportunity and investigate whether the existing multi-epoch observations obtained with the VLTI for 68 pre-main sequence stars provide evidence for the variability of the brightness distributions of the innermost few astronomical units of protoplanetary disks and to quantify any variations detected. We find seven objects with significant variations. By classifying the symmetry of the variations, we find that in addition to the two known binaries DX Cha and AK Sco, HD 50138 and V856 Sco show signs of variability caused by variations of asymmetric structures in the brightness distributions.

References

Kobus et al. (2020) A&A, 642, A104

Author(s): Fabio Del Sordo

Abstract:

The present understanding of stellar dynamos still lacks a clear mechanism linking it to magnetic interaction between planets on close-in orbits and their host stars. I here present an analytical model based on the solution for a stellar α-squared dynamo surrounded by a force-free corona and an outer layer consistent with the presence of a Parker stellar wind. This analytical model allows for making predictions on different scenarios. For example, I will show how magnetized close-in exoplanets, such as hot Jupiters, have either no effect or can suppress the stellar dynamo. The first case is related to non-evaporating exoplanets, whilst the second emerges when planetary evaporation is present and implies the presence of currents in the stellar corona. This model may explain the low activity observed for some exoplanet host stars such as HD 209458b, 51 Pegasi, Wasp 18, and GJ1151. I will also present some global numerical MHD simulations of stellar dynamos to show the central role played by boundary conditions. Magnetic star-planet interaction can therefore quench stellar dynamo, significantly lowering the level of magnetic activity of stars hosting hot Jupiters.

References

Bonanno, A., and Del Sordo, F., A&A 605, A33 (2017)

Author(s): Urs Schäfer and Anders Johansen

Abstract:

The streaming instability is arguably the most promising mechanism to induce the formation of planetesimals, a key step in the growth from dust grains to planets. Nonetheless, planetesimal formation via the streaming instability has been found in previous studies to require either a dust-to-gas ratio or a dust size that is enhanced compared to observed values. We employ two-dimensional adaptive mesh refinement simulations of protoplanetary disks on a global scale to investigate dust concentration and the potential for planetesimal formation owing to the streaming instability in concert with another hydrodynamic instability, the vertical shear instability. Our simulations show that the two instabilities in conjunction can cause dust concentration that is sufficient for planetesimal formation for lower dust-to-gas ratios and smaller dust sizes than the streaming instability in isolation, and in particular under conditions that are consistent with observational constraints. This is because dust accumulating in pressure bumps induced by the vertical shear instability seeds the streaming instability, which in turn reinforces both pressure bumps and dust accumulations. While our two-dimensional model does not include self-gravity, we find that the formation of strong, gravitationally unstable dust concentrations can be robustly inferred from the maximum or the mean dust-to-gas density ratio, though not from the mid-plane density ratio. The latter is since the vertical shear instability in our model of both instabilities puffs up the dust layer to a larger scale height and thus a lower mid-plane dust-to-gas density ratio than the streaming instability in our model of only this instability.

Author(s): Momo Ellwarth, Birte Ehmann, Sebastian Schäfer, Ansgar Reiners

Abstract:

High spectral resolution observations of the Sun at different centre-to-limb angles are crucial to get a better understanding of how solar and stellar activity affects radial-velocity measurements in general and therewith also perturb the detection of Earth-like planets. Such observations are also essential to improve further 3D MHD simulations.

This talk will give an overview about spatially resolved solar observations taken at the Institute for Astrophysics and Geophysics in Göttingen and present first outcomes of the observed spectra. We observe the spatially resolved solar surface (Ø 32 arcsec) using a high-resolution Fourier Transform Spectrograph with a resolution of R~700,000 (at lambda ~600nm) for the entire visible band-pass (~ 450 to 1000 nm). We created a quiet Sun atlas covering 14 different heliocentric positions with a total number of 166 observations.

The obtained solar atlas provides crucial information about limb-darkening, convective velocities, and line profile variability. In this talk there will be shown first results of single lines and their corresponding bisectors at different limb angles. This lines sometimes differs quite a lot from 3D MHD simulations. Additionally we want to give an idea about the general behaviour of Fe I lines over the disc.
We hope that those atlases will be very valuable to the community, to further improve our understanding of the solar photosphere and of stars in general.

Author(s): David Melon Fuksman and Hubert Klahr

Abstract:

Theoretical models of irradiated protoplanetary disks often obtain a spontaneous amplification of scale height perturbations produced by the enhanced absorption of starlight in enlarged regions. In turn, such regions cast shadows on adjacent zones that consequently cool down and shrink, eventually leading to an alternating pattern of overheated and shadowed regions. Previous investigations have proposed this to be a real self-sustained process, the so-called self-shadowing or thermal wave instability, which could naturally form frequently observed disk structures such as rings and gaps, and even potentially enhance the formation of planetesimals. All of these, however, have assumed in one way or another vertical hydrostatic equilibrium and instantaneous radiative diffusion throughout the disk. In this work we present the first study of the stability of accretion disks to self-shadowing that relaxes these assumptions, relying instead on radiation-hydrodynamical simulations. Our results suggest that radiative cooling and gas advection at the disk surface prevent a self-shadowing instability from forming by damping temperature perturbations before these reach lower, optically thick regions.

References

Melon Fuksman & Klahr, Accepted for publication in ApJ. https://arxiv.org/abs/2207.05106