arXiv subjects

Christoph Mordasini

Publications and source records attributed to Christoph Mordasini.

At least 37 records · Page 2Linked to original sources

arXiv2025

Competing chemical signatures in the atmosphere of TOI-270 d: Inference of sulfur and carbon chemistry

Recent JWST measurements allow access to the near-infrared spectrum of the sub-Neptune TOI-270 d, for which two different interpretations, a high-metallicity miscible envelope and a lower metallicity hycean world, are currently in conflict. Here, we reanalyze the published data and reproduce previously retrieved molecular abundances based on an independent data reduction and a different retrieval framework. The aim of this study is to refine the understanding of TOI-270 d and highlight considerations for JWST data analysis. Additionally, we test the impact of data resolution on atmospheric retrieval calculations. We reduce one JWST NIRSpec G395H and one NIRISS SOSS GR700XD transit dataset using the Eureka! pipeline and a custom MCMC-based light curve fitting algorithm at the instruments' native resolutions. The atmospheric composition is estimated with the updated BeAR retrieval code across a grid of retrieval setups and spectral resolutions. Our transit spectrum is consistent with previous studies, except at the red end of the NIRISS data. Our retrievals support a higher mean molecular weight atmosphere for TOI-270 d. We provide refined abundance constraints and find statistically favored model extensions indicating either sulfur-rich chemistry with species such as CS2, CS, and H2CS, or the possible presence of CH3Cl or CH3F. However, Bayesian inference cannot distinguish between these scenarios due to similar opacities below 4 microns. Our analysis reinforces TOI-270 d as a highly interesting warm sub-Neptune for atmospheric studies, with a complex chemistry in a cloud-free upper atmosphere. However, its exact nature remains uncertain and warrants further detailed photochemical modeling and observations.

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arXiv2025

The New Generation Planetary Population Synthesis (NGPPS). VII. Statistical comparison with the HARPS/Coralie survey

We seek to quantify the fidelity with which modern population syntheses reproduce observations in view of their use as predictive tools. We compared synthetic populations from the Generation 3 Bern Model of Planet Formation and Evolution (core accretion, solar-type host stars) and the HARPS/Coralie radial velocity sample. We biased the synthetic planet population according to the completeness of the observed data and performed quantitative statistical comparisons and systematically identified agreements and differences. Our nominal population reproduces many of the main features of the HARPS planets: two main groups of planets (close-in sub-Neptunes and distant giants), a bimodal mass function with a less populated `desert', an observed mean multiplicity of about 1.6, and several key correlations. The remaining discrepancies point to areas that are not fully captured in the model. For instance, we find that the synthetic population has 1) in absolute terms too many planets by ~70%, 2) a `desert' that is too deep by ~60%, 3) a relative excess of giant planets by ~40%, 4) planet eccentricities that are on average too low by a factor of about two (median of 0.07 versus 0.15), and 5) a metallicity effect that is too weak. Finally, the synthetic planets are overall too close to the star compared to the HARPS sample. The differences allowed us to find model parameters that better reproduce the observed planet masses, for which we computed additional synthetic populations. We find that physical processes appear to be missing and that planets may originate on wider orbits than our model predicts. Mechanisms leading to higher eccentricities and slower disc-limited gas accretion also seem necessary. We advocate that theoretical models should make a quantitative comparison between the many current and future large surveys to better understand the origins of planetary systems. (Abridged.)

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arXiv2025

Atmospheric composition and circulation of the ultra-hot Jupiter WASP-121b with joint NIRPS, HARPS and CRIRES+ transit spectroscopy

Ultra-hot Jupiters like WASP-121b provide unique laboratories for studying atmospheric chemistry and dynamics under extreme irradiation. Constraining their composition and circulation is key to tracing planet formation pathways. We present a comprehensive characterisation of WASP-121b using high-resolution transit spectroscopy from HARPS, NIRPS, and CRIRES+ across nine transits, complemented by five TESS sectors, two EulerCam light curves simultaneous with HARPS/NIRPS, and an extensive RV dataset refining orbital parameters. Cross-correlation detects Fe, CO, and V with SNRs of 5.8, 5.0, and 4.7, respectively. Retrieval analysis constrains H$_2$O to $-6.52^{+0.49}_{-0.68}$ dex, though its signal might be muted by the H$^-$ continuum. We measure volatile/refractory ratios, key to uncover planetary chemistry, evolution, and formation. Retrieved values align with solar composition in chemical equilibrium, suggesting minimal disequilibrium chemistry at the probed pressures (around $10^{-4}$-$10^{-3}$ bar). We update WASP-121b's orbital parameters analysing its largest RV dataset to date. Comparing orbital velocities from RVs and atmospheric retrieval reveals a non-zero circulation offset, $\mathrm{ΔK}_{\mathrm{p}} = -15 \pm 3 \ \mathrm{km}\mathrm{s}^{-1}$ (assuming $\mathrm{M}_{\star} = 1.38 \pm 0.02 \ \mathrm{M}_{\odot}$), consistent with drag-free or weak-drag 3D GCM predictions, though sensitive to stellar mass. These results provide new constraints on WASP-121b's thermal structure, dynamics, and chemistry, underscoring the power of multi-instrument and multi-wavelength high-resolution spectroscopy to probe exoplanet atmospheres.

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arXiv2025

Quantifying thermal water dissociation in the dayside photosphere of WASP-121 b using NIRPS

The intense stellar irradiation of ultra-hot Jupiters results in some of the most extreme atmospheric environments in the planetary regime. On their daysides, temperatures can be sufficiently high for key atmospheric constituents to thermally dissociate into simpler molecular species and atoms. This dissociation drastically changes the atmospheric opacities and, in turn, critically alters the temperature structure, atmospheric dynamics, and day-night heat transport. To this date, however, simultaneous detections of the dissociating species and their thermally dissociation products in exoplanet atmospheres have remained rare. Here we present the simultaneous detections of H$_2$O and its thermally dissociation product OH on the dayside of the ultra-hot Jupiter WASP-121 b based on high-resolution emission spectroscopy with the recently commissioned Near InfraRed Planet Searcher (NIRPS). We retrieve a photospheric abundance ratio of log$_{10}$(OH/H$_2$O) $= -0.15\pm{0.20}$ indicating that there is about as much OH as H$_2$O at photospheric pressures, which confirms predictions from chemical equilibrium models. We compare the dissociation on WASP-121 b with other ultra-hot Jupiters and show that a trend in agreement with equilibrium models arises. We also discuss an apparent velocity shift of $4.79^{+0.93}_{-0.97} $km s$^{-1}$ in the H$_2$O signal, which is not reproduced by current global circulation models. Finally, in addition to H$_2$O and OH, the NIRPS data reveal evidence of Fe and Mg, from which we infer a Fe/Mg ratio consistent with the solar and host star ratios. Our results demonstrate that NIRPS can be an excellent instrument to obtain simultaneous measurements of refractory and volatile molecular species, paving the way for many future studies on the atmospheric composition, chemistry, and the formation history of close-in exoplanets.

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arXiv2025

Diving into the planetary system of Proxima with NIRPS -- Breaking the metre per second barrier in the infrared

We obtained 420 high-resolution spectra of Proxima, over 159 nights, using the Near Infra Red Planet Searcher (NIRPS). We derived 149 nightly binned radial velocity measurements with a standard deviation of 1.69 m/s and a median uncertainty of 55 cm/s, and performed a joint analysis combining radial velocities, spectroscopic activity indicators, and ground-based photometry, to model the planetary and stellar signals present in the data, applying multi-dimensional Gaussian process regression to model the activity signals. We detect the radial velocity signal of Proxima b in the NIRPS data. All planetary characteristics are consistent with those previously derived using visible light spectrographs. In addition, we find evidence of the presence of the sub-Earth Proxima d in the NIRPS data. When combining the data with the HARPS observations taken simultaneous to NIRPS, we obtain a tentative detection of Proxima d and parameters consistent with those measured with ESPRESSO. By combining the NIRPS data with simultaneously obtained HARPS observations and archival data, we confirm the existence of Proxima d, and demonstrate that its parameters are stable over time and against change of instrument. We refine the planetary parameters of Proxima b and d, and find inconclusive evidence of the signal attributed to Proxima c (P = 1900 d) being present in the data. We measure Proxima b and d to have minimum masses of 1.055 $\pm$ 0.055 Me, and 0.260 $\pm$ 0.038 Me, respectively. Our results show that, in the case of Proxima, NIRPS provides more precise radial velocity data than HARPS, and a more significant detection of the planetary signals. The standard deviation of the residuals of NIRPS after the fit is 80 cm/s, showcasing the potential of NIRPS to measure precise radial velocities in the near-infrared.

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arXiv2025

Blind search for activity-sensitive lines in the near-infrared using HARPS and NIRPS observations of Proxima and Gl 581

Stellar activity variability is one of the main obstacles to the detection of Earth-like planets using the RV method. The aim of this work is to measure the effect of activity in the spectra of M dwarfs and detect activity-sensitive lines in the NIR. We took advantage of the simultaneous observations of HARPS and the newly commissioned NIRPS spectrograph to carry out a blind search of the most activity-sensitive spectral lines in the NIR using NIRPS spectra and known activity indicators in the optical from HARPS as a reference. We analysed the spectra of Proxima (M5.5V) and Gl 581 (M3V), two M dwarfs with different activity levels and internal structures. Spectral lines were identified for both stars and their profiles were fitted using different models. We found hundreds of lines sensitive to activity for both stars; the Proxima spectra were more affected. For Proxima, 32% of the identified lines can be used to measure the rotation period of the star, while for Gl 581 the numbers drops to 1%. The fraction of lines sensitive to activity increases with increasing line depth. A list of 17 lines with rotation period detection for both stars is provided. Stellar activity is able to affect a significant number of spectral lines in the NIR, and methods should be developed to mitigate those effects at the spectral level. The line distortions detected here are expected to come mainly from the flux effect due to temperature contrasts between active regions and the quiet photosphere; however, we cannot rule out the possibility that core-emission from chromospheric activity or Zeeman splitting are also affecting some lines. The new line lists presented here can be used to improve the RV extraction and the detection of RV variability due to stellar activity signals, and to help false positive detection and the modelling of activity variability, thereby enhancing exoplanet detection in the NIR.

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arXiv2025

NIRPS detection of delayed atmospheric escape from the warm and misaligned Saturn-mass exoplanet WASP-69b

Near-infrared high-resolution echelle spectrographs unlock access to fundamental properties of exoplanets, from their atmospheric escape and composition to their orbital architecture, which can all be studied simultaneously from transit observations. We present the first results of the newly commissioned ESO near-infrared spectrograph, NIRPS, from three transits of WASP-69b. We used the RM Revolutions technique to better constrain the orbital architecture of the system. We extracted the high-resolution helium absorption profile to study its spectral shape and temporal variations. Then, we made 3D simulations from the EVE code to fit the helium absorption time series. We measure a slightly misaligned orbit for WASP-69b (psi of 28.7+/-5.7 deg). We confirm the detection of helium with an average excess absorption of 3.17+/-0.05%. The helium absorption is spectrally and temporally resolved, extends to high altitudes and has a strong velocity shift up to -29.5+/-2.5 km/s 50 minutes after egress. EVE simulations put constraints on the mass loss of 2.25 10^11 g/s and hint at reactive chemistry within the cometary-like tail and interaction with the stellar winds that allow the metastable helium to survive longer than expected. Our results suggest that WASP-69b is undergoing a transformative phase in its history, losing mass while evolving on a misaligned orbit. This work shows how combining multiple observational tracers such as orbital architecture, atmospheric escape, and composition, is critical to understand exoplanet demographics and their formation and evolution. We demonstrate that NIRPS can reach precisions similar to HARPS for RM studies, and the high data quality of NIRPS leads to unprecedented atmospheric characterization. The high stability of NIRPS combined with the large GTO available for its consortium, enables in-depth studies of exoplanets as well as large population surveys.

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arXiv2025

Hydride ion continuum hides absorption signatures in the NIRPS near-infrared transmission spectrum of the ultra-hot gas giant WASP-189b

Ultra-hot Jupiters showcase extreme atmospheric conditions, including molecular dissociation, ionisation, and significant day-to-night temperature contrasts. Their close proximity to host stars subjects them to intense stellar irradiation, driving high temperatures where hydride ions (H$^-$) significantly contribute to opacity, potentially obscuring metal features in near-infrared transmission spectra. We investigate the atmosphere of WASP-189b, targeting atomic, ionic, and molecular species (H, He, Fe, Ti, V, Mn, Na, Mg, Ca, Cr, Ni, Y, Ba, Sc, Fe$^+$, Ti$^+$, TiO, H$_2$O, CO, and OH), focusing on (i) the role of H$^-$ as a source of continuum opacity, and (ii) the relative hydride-to-Fe abundance using joint optical and near-infrared data. We present two transits of WASP-189b gathered simultaneously in the optical with HARPS and near-infrared with NIRPS, supported by photometric light curves from EulerCam and ExTrA. Transmission spectra were analysed via cross-correlation to detect absorption features and enhance the signal-to-noise ratio. Atmospheric retrievals quantified relative abundances by fitting overall metallicity and proxies for TiO, H$^-$, and e$^-$. Only atomic iron is detected in HARPS data (S/N ~5.5), but not in NIRPS, likely due to H$^-$ continuum dampening. Retrievals on HARPS-only and HARPS+NIRPS suggest the hydride-to-Fe ratio exceeds equilibrium predictions by about 0.5 dex, hinting at strong hydrogen ionisation. Including NIRPS data helps constrain H$^-$ abundance and set an upper limit on free electron density, unconstrained in HARPS-only data. These results emphasise H$^-$ as a significant continuum opacity source impeding detection of planetary absorption features in WASP-189b's near-infrared transmission spectrum.

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arXiv2025

The New Generation Planetary Population Synthesis (NGPPS) VIII. Impact of host star metallicity on planet occurrence rates, orbital periods, eccentricities, and radius valley morphology

The dust-to-gas ratio in the protoplanetary disk, which is likely imprinted into the host star metallicity, is a property that plays a crucial role during planet formation. We aim at constraining planet formation and evolution processes by statistically analysing planetary systems generated by the Generation III Bern model, comparing with the correlations derived from observational samples. Using synthetic planets biased to observational completeness, we find that (1) the occurrence rates of large giant planets and Neptune-size planets are positively correlated with [Fe/H], while small sub-Earths exhibit an anti-correlation. In between, for sub-Neptune and super-Earth, the occurrence rate first increases and then decreases with increasing [Fe/H] with an inflection point at 0.1 dex. (2) Planets with orbital periods shorter than ten days are more likely to be found around stars with higher metallicity, and this tendency weakens with increasing planet radius. (3) Both giant planets and small planets exhibit a positive correlation between the eccentricity and [Fe/H], which could be explained by the self-excitation and perturbation of outer giant planets. (4) The radius valley deepens and becomes more prominent with increasing [Fe/H], accompanied by a lower super-Earth-to-sub-Neptune ratio. Furthermore, the average radius of the planets above the valley increases with [Fe/H]. Our nominal model successfully reproduces many observed correlations with stellar metallicity, supporting the description of physical processes and parameters included in the Bern model. However, the dependences of orbital eccentricity and period on [Fe/H] predicted by the synthetic population is however significantly weaker than observed. This discrepancy suggests that long-term dynamical interactions between planets, along with the impact of binaries/companions, can drive the system towards a dynamically hotter state.

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arXiv2025

Modelling the 3D atmospheric structure of the cold Jupiter WD1856+534b orbiting a white dwarf

WD-1856b+534b (WD-1856b) is to date the only detected cold Jupiter outside of our Solar System. This cold Jupiter can provide useful information about the cold giants in our Solar System. Recent JWST observations have targeted WD-1856b, with more scheduled in the near future. To support the interpretation of these observations, we simulated WD-1856b using a three-dimensional (3D) General Circulation Model (GCM) and produced synthetic emission spectra of the planet. We used the Exo-FMS GCM with correlated-k radiative transfer (RT) and mixing-length theory (MLT). In addition, we included abundances of 13 chemical species using the thermochemical kinetic model mini-chem. Because there are substantial uncertainties in the metallicity and internal temperature of WD-1856b, we ran simulations with 1x, 10x, and 100x solar compositions and at low and high internal temperatures (100 K and 500 K). We generated emission spectra and brightness temperature curves with the GCM output using the 3D Monte Carlo radiative-transfer code gCMCRT. Our results suggest larger volume mixing ratios (VMR) of CO and \CO2 with a warmer core at higher metallicity. With a colder core, H2O and CH4 become more relevant and increase to 0.01 VMR at 100x Solar. We suggest possible \H2O cloud formation in the upper atmosphere in the warm 100x solar case and in all cold cases, which may reduce gas phase H2O in the upper atmosphere moderately.

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arXiv2025

Semi-analytical model for the dynamical evolution of planetary system II: Application to systems formed by a planet formation model

The standard formation model of close-in low-mass planets involves efficient inward migration followed by growth through giant impacts after the protoplanetary gas disk disperses. While detailed N-body simulations have enhanced our understanding, their high computational cost limits statistical comparisons with observations. In our previous work, we introduced a semi-analytical model to track the dynamical evolution of multiple planets through gravitational scattering and giant impacts after the gas disk dispersal. Although this model successfully reproduced N -body simulation results under various initial conditions, our validation was still limited to cases with compact, equally-spaced planetary systems. In this paper, we improve our model to handle more diverse planetary systems characterized by broader variations in planetary masses, semi-major axes, and orbital separations and validate it against recent planet population synthesis results. Our enhanced model accurately reproduces the mass distribution and orbital architectures of the final planetary systems. Thus, we confirm that the model can predict the outcomes of post-gas disk dynamical evolution across a wide range of planetary system architectures, which is crucial for reducing the computational cost of planet formation simulations.

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arXiv2025

The importance of the dynamical corotation torque for the migration of low-mass planets -- 1D analytical prescriptions verified by 2D hydrodynamical simulations

Recent developments suggested that planet formation occurs in regions of the discs with low turbulent viscosity. There, the dynamical corotation torque is thought to play an important role by slowing down type I migration. We aim to provide a simple analytical prescription for the dynamical corotation torque for use in 1D global models of planet formation and evolution, and assess the importance of the dynamical corotation torque for the migration of low-mass planets in low-viscosity discs. We propose simple prescriptions for calculating in 1D the time evolution of the vortensities of the librating and orbit-crossing flows around a low-mass planet, which both enter the analytical expression for the dynamical corotation torque. One of our prescriptions involves a memory timescale for the librating flow, and 2D hydrodynamical simulations of disc-planet interactions are used to assess the memory timescale and validate our model. The orbital evolution of a low-mass planet is calculated by 1D simulations where the dynamical corotation torque features our prescriptions for the vortensities of the librating and orbit-crossing flows, and by 2D hydrodynamical simulations of disc-planet interactions, assuming locally isothermal discs. We find very good agreement between the 1D and 2D simulations for a wide parameter space, whether the dynamical corotation torque slows down or accelerates inward migration. We provide maps showing how much the dynamical corotation torque reduces the classical type I migration torque as a function of planet mass and orbital distance. The reduction is about 50\% for a 10 Earth-mass planet at 10 au in a young disc with surface density profile in $r^{-1/2}$ and alpha viscosity of $10^{-4}$. In discs with low turbulent viscosity, the dynamical corotation torque should be taken into account in global models as it can strongly slow down type I migration.

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arXiv2025

The NCORES Program: Precise planetary masses, null results, and insight into the planet mass distribution near the radius gap

NCORES was a large observing program on the ESO HARPS spectrograph, dedicated to measuring the masses of Neptune-like and smaller transiting planets discovered by the TESS satellite using the radial velocity technique. This paper presents an overview of the programme, its scientific goals and published results, covering 35 planets in 18 planetary systems. We present spectrally derived stellar characterisation and mass constraints for five additional TOIs where radial velocity observations found only marginally significant signals (TOI-510.01, $M_p=1.08^{+0.58}_{-0.55}M_\oplus$), or found no signal (TOIs 271.01, 641.01, 697.01 and 745.01). A newly detected non-transiting radial velocity candidate is presented orbiting TOI-510 on a 10.0d orbit, with a minimum mass of $4.82^{+1.29}_{-1.26}M_\oplus$, although uncertainties on the system architecture and true orbital period remain. Combining the NCORES sample with archival known planets we investigate the distribution of planet masses and compositions around and below the radius gap, finding that the population of planets below the gap is consistent with a rocky composition and ranges up to a sharp cut-off at $10M_\oplus$. We compare the observed distribution to models of pebble- and planetesimal-driven formation and evolution, finding good broad agreement with both models while highlighting interesting areas of potential discrepancy. Increased numbers of precisely measured planet masses in this parameter space are required to distinguish between pebble and planetesimal accretion.

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arXiv2024

Predictions of Dust Continuum Emission from a Potential Circumplanetary Disk: A Case Study of the Planet Candidate AB Aurigae b

Gas accreting planets embedded in protoplanetary disks are expected to show dust thermal emission from their circumplanetary disks (CPDs). However, a recently reported gas accreting planet candidate, AB Aurigae b, has not been detected in (sub)millimeter continuum observations. We calculate the evolution of dust in the potential CPD of AB Aurigae b and predict its thermal emission at 1.3 mm wavelength as a case study, where the obtained features may also be applied to other gas accreting planets. We find that the expected flux density from the CPD is lower than the 3-sigma level of the previous continuum observation by ALMA with broad ranges of parameters, consistent with the non-detection. However, the expected planet mass and gas accretion rate are higher if the reduction of the observed near-infrared continuum and H-alpha line emission due to the extinction by small grains is considered, resulting in higher flux density of the dust emission from the CPD at (sub)millimeter wavelength. We find that the corrected predictions of the dust emission are stronger than the 3-sigma level of the previous observation with the typical dust-to-gas mass ratio of the inflow to the CPD. This result suggests that the dust supply to the vicinity of AB Aurigae b is small if the planet candidate is not the scattered light of the star but is a planet and has a CPD. Future continuum observations at shorter wavelength are preferable to obtain more robust clues to the question whether the candidate is a planet or not.

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arXiv2024

Convective mixing in distant and close-in giant planets -- Dependences on the initial composition, luminosity, bloating and semi-convection

Recent structure models of Jupiter suggest the existence of an extended region in the deep interior with a high heavy element abundance, referred to as a dilute core. This finding has led to increased interest in modelling the formation and evolution processes with the goal of understanding how and under what circumstances such a structure is formed and retained, to in turn better understand the relation between atmospheric and bulk metallicity. We modelled the evolution of giant planets, varying various parameters relevant for the convective mixing process, such as the mixing length parameter and the size of the mesh, and parameters related to the general evolution, such as the orbital distance and the initial luminosity. We in particular studied hot Jupiters and find that the effect of bloating on the mixing process is small but can in some cases inhibit convective mixing by lowering the intrinsic luminosity for a given entropy. Semi-convection can significantly lower the extent of a dilute core if it is strong enough. We find that dilute cores are unable to persist for initial luminosities much higher than 3 x 1e3 LJ for a Jupiter-like planet for the initial heavy element profiles we studied. From this we conclude that, based on our model, it is unlikely that a large number of giant planets retain a dilute core throughout their evolution, although this is dependent on the assumptions and limitations of our method. Future work should focus on improving the link between formation and evolution models so that the mixing process is accurately modelled throughout a planet's lifetime and on improving the understanding of how to model convection near radiative-convective boundaries.

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arXiv2024

In-situ observations of resident space objects with the CHEOPS space telescope

The CHaracterising ExOPlanet Satellite (CHEOPS) is a partnership between the European Space Agency and Switzerland with important contributions by 10 additional ESA member States. It is the first S-class mission in the ESA Science Programme. CHEOPS has been flying on a Sun-synchronous low Earth orbit since December 2019, collecting millions of short-exposure images in the visible domain to study exoplanet properties. A small yet increasing fraction of CHEOPS images show linear trails caused by resident space objects crossing the instrument field of view. To characterize the population of satellites and orbital debris observed by CHEOPS, all and every science images acquired over the past 3 years have been scanned with a Hough transform algorithm to identify the characteristic linear features that these objects cause on the images. Thousands of trails have been detected. This statistically significant sample shows interesting trends and features such as an increased occurrence rate over the past years as well as the fingerprint of the Starlink constellation. The cross-matching of individual trails with catalogued objects is underway as we aim to measure their distance at the time of observation and deduce the apparent magnitude of the detected objects. As space agencies and private companies are developing new space-based surveillance and tracking activities to catalogue and characterize the distribution of small debris, the CHEOPS experience is timely and relevant. With the first CHEOPS mission extension currently running until the end of 2026, and a possible second extension until the end of 2029, the longer time coverage will make our dataset even more valuable to the community, especially for characterizing objects with recurrent crossings.

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arXiv2024

Planetary population synthesis

The planetary population synthesis method aims at comprehensively testing planet formation theories against observational evidence and providing theoretical sets of planets to help interpret observations and inform instrument development. Recent developments on the theoretical and observational sides are reviewed: First, observational constraints are summarized, then, the work flow of population synthesis and its two main components are presented, which are, global end-to-end models of planetary formation and evolution and probability distributions for the disk initial conditions. Next, the output of four recent population synthesis models is compared in detail and differences and similarities are discussed. The goal is to help the reader understand the assumptions that were made and how they impact the results. Furthermore, future directions of research are identified and the impact of current and future observational programs is discussed. With JWST, evidence on disk and planet compositions emerges. Planet formation models need to prepare for these near-future developments by including self-consistent magnetic wind-driven gas and dust disk evolution, planetary migration, as well as employ hybrid pebble and planetesimal accretion, which are identified as dominant modes of accretion in different mass regimes.

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arXiv2024

RISTRETTO: reflected-light exoplanet spectroscopy at the diffraction limit of the VLT

RISTRETTO is a visible high-resolution spectrograph fed by an extreme adaptive optics (AO) system, to be proposed as a visitor instrument on ESO VLT. The main science goal of RISTRETTO is to pioneer the detection and atmospheric characterisation of exoplanets in reflected light, in particular the temperate rocky planet Proxima b. RISTRETTO will be able to measure albedos and detect atmospheric features in a number of exoplanets orbiting nearby stars for the first time. It will do so by combining a high-contrast AO system working at the diffraction limit of the telescope to a high-resolution spectrograph, via a 7-spaxel integral-field unit (IFU) feeding single-mode fibers. Further science cases for RISTRETTO include the study of accreting protoplanets such as PDS70b/c through spectrally-resolved H-alpha emission, and spatially-resolved studies of Solar System objects such as icy moons and the ice giants Uranus and Neptune. The project is in the manufacturing phase for the spectrograph sub-system, and the preliminary design phase for the AO front-end. Specific developments for RISTRETTO include a novel coronagraphic IFU combining a phase-induced amplitude apodizer (PIAA) to a 3D-printed microlens array feeding a bundle of single-mode fibers. It also features an XAO system with a dual wavefront sensor aiming at high robustness and sensitivity, including to pupil fragmentation. RISTRETTO is a pathfinder instrument in view of similar developments at the ELT, in particular the SCAO-IFU mode of ELT-ANDES and the future ELT-PCS instrument.

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