Warm giant exoplanets exhibit strong three-dimensional temperature contrasts that can significantly alter atmospheric chemistry through quenching and photochemistry, yet transmission spectra are commonly interpreted using one-dimensional, limb-averaged models. Such simplifications may bias inferred atmospheric properties, particularly metallicity and C/O ratio. In this work we investigate the relative influence of atmospheric composition and three-dimensional thermal structure on atmospheric chemistry and transmission spectra using WASP-69b as a test case. WASP-69b is a 900K warm Saturn, residing in a thermal regime especially sensitive to disequilibrium chemistry. We use three-dimensional general circulation model derived pressure-temperature profiles as inputs for a one-dimensional photochemical-kinetics model to resolve longitudinal and latitudinal chemical asymmetries across the atmosphere. We find that CH4 exhibits strong latitudinal variations linked to deep quench temperatures, while SO2 shows longitudinal asymmetries driven by upper-atmospheric photochemistry and irradiation geometry. In contrast, CO2 remains comparatively insensitive to spatial thermal variations and emerges as a robust tracer of atmospheric metallicity. Synthethic transmission spectra reveal that three-dimensional chemical asymmetries can produce spectral variations comparable to those induced by metallicity itself, demonstrating that limb-averaged interpretations can mask substantial spatial structure in warm giant exoplanet atmospheres.

Understanding planetary habitability requires a comparative approach that explores the divergent evolutionary outcomes of Earth and Venus. The Habitable Worlds Observatory (HWO) will be uniquely positioned to conduct a statistical and physical census of terrestrial exoplanets spanning the Venus Zone (VZ) and the Habitable Zone, enabling the detection and atmospheric characterization of post-runaway greenhouse worlds ("exoVenuses"). We present an updated list of VZ exoplanets, which raises the number of known candidates to 370. We describe a science case and an observing strategy for VZ exoplanets that integrates precursor exoplanet detection data and stellar characterization with HWO direct imaging, spectroscopy across the UV/optical/IR, and spectropolarimetry. Our proposed framework emphasizes a pathway toward the diagnosis of sulfur chemistry (SO2) and aerosol physics (H2SO4 clouds/hazes), planetary redox states (O2/O3 false positives from hydrogen loss), and cloud microphysics detection (rainbow polarization). We quantify implications for HWO requirements, including UV access to 0.2-0.4 mu m, optical/NIR coverage to greater than or similar to 1.5 mu m, inner working angle (IWA) reaching 0.3-1.5 au around nearby Sun-like stars, and the SNR/resolution needed for key features. Finally, we outline a community-driven path to producing robust demographic inferences and target selection for optimizing HWO observations.

This study investigates the thermal stability and absorption of metal oxide clusters in exoplanetary atmospheres. Utilizing our thermochemical data, we analyze eight distinct cluster families: magnesium oxide (MgO), silicon monoxide (SiO), titanium monoxide (TiO), vanadium monoxide (VO), titanium dioxide (TiO$_2$), vanadium dioxide (VO$_2$), aluminum oxide (Al$_2$O$_3$), and vanadium pentoxide (V$_2$O$_5$). Equilibrium cluster populations as a function of gas temperature and pressure reveal distinct stability regimes. Under solar elemental abundances, (TiO$_2$)$\rm\rm_N$ and (Al$_2$O$_3$)$\rm_N$ are favored at higher temperatures, while (MgO)$\rm_N$ and (SiO)$\rm_N$ dominate at lower temperatures. Computed absorption spectra exhibit strong size- and composition-dependent absorption features in the mid-infrared (8--50~$μ$m), many of which fall within the wavelength range accessible to \texttt{JWST/MIRI}. We further coupled cluster thermodynamics with 3D general circulation model (GCM) outputs to investigate the cluster stability across the ultra-hot Jupiters (UHJs) WASP-121 b and WASP-18 b, the hot Jupiter (HJ) WASP-39 b, and the warm Jupiter (WJ) WASP-69 b. In WASP-121 b and WASP-18 b, extreme dayside temperatures suppress large-cluster stability, yielding atmospheres dominated by metal ions at low pressures and neutral metals at depth, with limited cluster survival on the nightside and morning terminator. In WASP-39 b, larger clusters are not thermochemically favoured despite the enhanced metallicity; instead, equilibrium chemistry stabilises smaller species, with only TiO showing a tendency toward stable larger cluster forms, likely due to its open d-orbitals. In contrast, WASP-69 b favors the formation of larger metal oxide clusters across an extended pressure range, highlighting WJs as a favorable environment for metal oxide cluster stability.

The prevalence of atmospheres on rocky planets is one of the major questions in exoplanet astronomy, but there are currently no published unambiguous detections of atmospheres on any rocky exoplanets. The MIRI instrument on JWST can measure thermal emission from tidally locked rocky exoplanets orbiting small, cool stars. This emission is a function of their surface and atmospheric properties, potentially allowing detections of atmospheres. One way to find atmospheres is to search for lower dayside emission than would be expected for a blackbody planet. Another technique is to measure phase curves of thermal emission to search for nightside emission due to atmospheric heat redistribution. Here, we compare strategies for detecting atmospheres on rocky exoplanets. We simulate secondary eclipse and phase curve observations in the MIRI F1500W and F1280W filters for a range of surfaces (providing our open-access albedo data) and atmospheres on 30 exoplanets selected for their F1500W signal-to-noise ratio. We show that secondary eclipse observations are more degenerate between surfaces and atmospheres than suggested in previous work, and that thick atmospheres can support emission consistent with a blackbody planet in these filters. These results make it difficult to unambiguously detect or rule out atmospheres using their photometric dayside emission alone. We suggest that an F1500W phase curve could instead be observed for a similar sample of planets. While phase curves are time-consuming and their instrumental systematics can be challenging, we suggest that they allow the only unambiguous detections of atmospheres by nightside thermal emission.

The discovery of many low-mass exoplanets, including several planets within the habitable zone of their host stars, has led to the question of which kind of atmosphere surrounds them. Recent exoplanet detections have revealed the existence of a large population of low-mass planets (<3 M ⊕) with H2-dominated atmospheres that must have been accreted from the protoplanetary disk. As the gas disk usually has an ~10% fraction of helium, we model the possible enrichment of the primordial He fraction in the atmosphere of planets with mass between 0.75 M ⊕ and 3.0 M ⊕ that orbit in the classical habitable zone of Sun-like stars. Depending on the mass accreted by the planet during the gas disk phase and the stellar high-energy flux between ~10 and 120 nm, we find that Earth-like planets with masses between ~0.95 M ⊕ and 1.25 M ⊕ inside the habitable zone of Sun-like stars can end up with He-dominated primordial atmospheres. This finding has important implications for the evolution of Earth-like habitats, as these thick helium-enriched primordial atmospheres can inhibit the habitability of these planets. The upcoming generation of giant telescopes, such as the Extremely Large Telescope, may enable us to observe and explore these atmospheres.

The diversity of exoplanets provides a vast range of potential environments in which liquid water can exist: atmospheres, surfaces, sub-surfaces. Therefore, many environments provide the most fundamental requirement for life as we know it from Earth and could in principle be habitable. However, the presence of water is not the only necessity for life to form, especially the presence of nutrients (C, H, N, O, P, and S) is crucial for the formation of life as we know it.In order to further understand and constrain potentially habitable environments of diverse planets, we introduce the concept of nutrient availability to constrain the habitability of a planet. This framework is based on the concentrations of nutrient bearing molecules in the condensate and gas phase in the presence of liquid water.Applying this concept to a diverse set of atmospheres allows to provide constraints on the potential of surface and aerial biospheres. The atmospheric model used is a bottom-to-top equilibrium chemistry model, wich includes cloud formation. In order to cover the range of different atmospheric compositions, we investigate various different sets of element abundances and surface conditions.We find that reduced forms of C, N, and S are commonly found at the water cloud base for a range of different compositions of the planetary surface and atmosphere - even in overall oxidised atmospheres. In our model atmospheres, the only non-CHNOS elements in the atmosphere in the surrounding of liquid water clouds are F and Cl, which are present in the form of HF and HCl. Although the CHNOS elements are present, the absence of P and metals in the atmospheres could be a limiting factor on the formation and evolution of life in aerial biospheres.

Context. The inner regions of planet-forming disks are warm and dense. The chemical networks used for disk modelling so far were developed for a cold and dilute medium and do not include a complete set of pressure-dependent reactions. The chemical networks developed for planetary atmospheres include such reactions along with the inverse reactions related to the Gibb's free energies of the molecules. The chemical networks used for disk modelling are thus incomplete in this respect. Aims. We want to study whether thermodynamic equilibrium can be established in a planet-forming disk. We identify the regions in the disk most likely to reach thermodynamic equilibrium and determine the timescale over which this occurs. Methods. We employ the theoretical concepts used in exoplanet atmosphere chemistry for the disk modelling with PROtoplanetary DIsk MOdel (PRODIMO). We develop a chemical network called CHemistry Assembled from exoplanets and dIsks for Thermodynamic EquilibriA (CHAITEA) that is based on the UMIST 2022, STAND, and large DIscANAlysis (DIANA) chemical networks. It consists of 239 species. From the STAND network, we adopt the concept of reversing all gas-phase reactions based on thermodynamic data. We use single-point models for a range of gas densities and gas temperatures to verify that the implemented concepts work and thermodynamic equilibrium is achieved in the absence of cosmic rays and photoreactions including radiative associations and direct recombinations. We then study the impact of photoreactions and cosmic rays that lead to deviations from thermodynamic equilibrium. We explore the chemical relaxation timescales towards thermodynamic equilibrium. Lastly, we study the predicted 2D chemical structure of a typical T Tauri disk when using the new CHAITEA network instead of the large DIANA standard network, including photorates, cosmic rays, X-rays, and ice formation. Results. We find that abundances calculated with PRODIMO using the CHAITEA network agree with those from the equilibrium chemistry code Gleich-Gewichts-Chemie (GGchem) down to 600 K when the photorates, cosmic rays, and X-rays (benchmark) are absent. To measure the deviation between thermodynamic equilibrium and chemical kinetics, a measure, sigma, is introduced that evaluates the mean logarithmic deviation between the two abundance sets, which is <1% in the benchmark case. In the presence of photoreactions, based on a local Planck radiation field, sigma increases to similar to 0.1 across all densities and temperatures. When the cosmic-ray ionisation rate is increased from zero to about 10(-25) s(-1), sigma begins to become large (>1), affecting in particular the ions, and when it reaches the standard value of 10(-17) s(-1), sigma becomes >10. Low-temperature and low-density regions are more affected than high-temperature and high-density regions, as expected. The chemical relaxation timescales show a wide range, with both slow and fast chemical processes. The 2D disk models show that thermodynamic equilibrium cannot be established anywhere in the disk. However, a tiny, warm, high-density region directly behind the inner rim which is shielded from the cosmic rays, approaches thermodynamic equilibrium to some extent. In the warm intermittent molecular layer, which is observable, sigma >= 10, and sigma is even higher in other regions. Conclusions. We have developed a new chemical network, CHAITEA, that merges planetary chemistry with disk chemistry and have implemented it in the 2D thermochemical disk code PRODIMO. The inclusion of termolecular and reverse reactions changes the chemical structure in the inner disk that is probed by JWST.

Venus, Earth’s twin planet, has been explored by numerous spacecraft, yet its water inventory and implications for planetary evolution remain uncertain. The deuterium-to-hydrogen (D/H) ratio is a key tracer for understanding the history of water on Venus. Here, we reanalyze Venus Express magnetic field data to study ion cyclotron waves (ICWs) generated by picked up H$^+$ ions and, for the first time, D$^+$ ions in the extended exosphere. From these wave signatures, we derive altitude-dependent neutral density profiles of both H atoms and D isotopes over several Venus radii. The profiles indicate that the observed ICWs are primarily driven by energetic suprathermal particle populations, which dominate the extended exosphere, and originate in the thermosphere via electron-dissociative recombination of hydrogen-bearing molecular ions (e.g., HCO$^+$, DCO$^+$, HCO$_2^+$, DCO$_2^+$, OH$^+$, OD$^+$, H$_2^+$, HD$^+$) controlling atmospheric hydrogen escape. Using these densities, we estimate the escape rates of H atoms and D isotopes to be approximately $\SI{2.82e25}{s^{-1}}$ and $\SI{1.5e24}{s^{-1}}$, respectively. The average D/H ratio near the exobase level is $\sim$0.44. It decreases to $\sim$0.33 at around 10 Venus radii. These unexpected high D/H ratios are in agreement with observations of the increase of the D/H ratio in the Venus mesosphere, showing elevated D/H ratios above the main cloud layer. These results reveal that fractionation processes in the upper atmosphere are altitude- and species-dependent and highlight a strong link between suprathermal particles, upper atmospheric chemistry, and water loss. Finally, our findings provide new constraints on Venus’s exosphere and the evolution of its water inventory.

The distribution of different types of atmospheres and surfaces on rocky planets is one of the major questions in exoplanet astronomy, but there are currently no published unambiguous detections of atmospheres on any rocky exoplanets. The MIRI instrument on JWST can measure thermal emission from tidally locked rocky exoplanets orbiting small, cool stars. This emission is a function of their surface and atmospheric properties, potentially allowing the detection of atmospheres. One technique is to measure day-side emission to search for lower thermal emission than expected for a black-body planet due to atmospheric absorption features. Another technique is to measure phase curves of thermal emission to search for night-side emission due to atmospheric heat redistribution. In this work we compare strategies for detecting atmospheres on rocky exoplanets using these techniques. We simulate secondary eclipse and phase curve observations in the MIRI F1500W and F1280W filters, for a range of surfaces and atmospheres on thirty exoplanets selected for their F1500W signal-to-noise ratio. Our results show that secondary eclipse observations are highly degenerate between surfaces and atmospheres, given the wide range of potential surface albedos. We also show that thick atmospheres can support emission consistent with a black-body planet in these filters. These two results make it difficult to unambiguously detect or rule out atmospheres using their photometric day-side emission, except in a subset of CO_2-dominated atmospheres. We suggest that an F1500W phase curve could instead be observed for a similar sample of planets, allowing the unambiguous detection of atmospheres by night-side emission.

Life as we know it requires the presence of liquid water and the availability of nutrients, which are mainly based on the elements C, H, N, O, P, and S (CHNOPS) and trace metal micronutrients. We aim to understand the presence of these nutrients within atmospheres that show the presence of water cloud condensates, potentially allowing the existence of aerial biospheres. In this paper we introduce a framework of nutrient availability levels based on the presence of water condensates and the chemical state of the CHNOPS elements. These nutrient availability levels are applied to a set of atmospheric models based on different planetary surface compositions resulting in a range of atmospheric compositions. The atmospheric model is a bottom-to-top equilibrium chemistry atmospheric model which includes the atmosphere-crust interaction and the element depletion due to the formation of clouds. While the reduced forms of CNS are present at the water cloud base for most atmospheric compositions, P and metals are lacking. This indicates the potential bio-availability of CNS, while P and metals are limiting factors for aerial biospheres.

Motivation: Early during their formation the planets capture an amount of atmosphere from the protoplanetary disk (Ikoma et al. 2018, Odert et al. 2018, Lammer et al. 2020, Kimura and Ikoma 2020). An additional proportion of their atmosphere is provided during the magma ocean stage by interior degassing. The latter mechanism is assumed to be the main provider of the final atmospheric mass. Its composition is compromised by the source silicate mineral and its chemical characterization (Gaillard and Scaillet 2014, Herbort et al. 2020). Numerous studies support the degassing of the oxidized gas species H2O and CO2 as main contributions from the magma ocean phase (Abe and Matsui 1988, Abe 1993, Elkins-Tanton 2008, Schaefer et al. 2012, Lebrun et al. 2013, Lupu et al. 2014, Gaillard and Scaillet 2014, Salvador et al. 2017, Nikolaou et al. 2019). Previous work has also shown that H2O, in particular, plays a crucial role (Hamano et al. 2013, Katyal et al. 2019, Turbet et al. 2019) in thermal blanketing. H2O possibly leads to “long-term” (Hamano et al 2013) or “conditionally continuous” (Nikolaou et al. 2019) magma oceans that effectively cease to cool. Water also ties directly to the availability of hydrogen that drives hydrodynamic escape (Airapetian et al. 2017, Lammer et al. 2018). CO2 factors into both above processes, as well (Wordsworth and Pierrehumbert 2013, Odert et al. 2018). Constraining the H2O and CO2 abundances early after formation is indispensible to the planet’s thermal evolution and extensive modeling effort has been devoted to it. Their constraint would in particular help revisit which magma ocean types among transient-conditionally continuous-permanent (Nikolaou et al. 2019) are detectable in future exoplanetary missions (ARIEL, Tinetti et al. 2018; PLATO, Rauer et al. 2014). Method: In this work we focus on the combination of degassed and disk-captured atmosphere under the assumption of chemical equilibrium. Using simulations from the 1D Convective Ocean of Magma Radiative Atmosphere and Degassing model (Nikolaou et al. 2019) we obtain the thermal evolution and degassing tracks of a rocky planet. In order to evaluate the chemical abundances under equilibrium conditions we employ the thermodynamical model GGchem (Woitke et al. 2018). We explore the atmospheric conditions during the lifetime of a magma ocean under varying mineral compositions and protoplanetary disk contributions. We discuss the results in the context of the likely magma ocean types. A.N. and P.W. wish to thank the Erwin Schrödinger International Institute for Mathematics and Physics (ESI) of the University of Vienna, Thematic Programme on “Astrophysical Origins: Pathways from Star Formation to Habitable Planets” 2019, which enabled this collaboration.

With observational efforts moving from the discovery into the characterisation mode, systematic campaigns that cover large ranges of global stellar and planetary parameters will be needed. We aim to uncover cloud formation trends and globally changing chemical regimes due to the host star's effect on the thermodynamic structure of their atmospheres. We aim to provide input for exoplanet missions like JWST, PLATO, and Ariel, as well as potential UV missions ARAGO, PolStar or POLLUX. Pre-calculated 3D GCMs for M, K, G, F host stars are the input for our kinetic cloud model. Gaseous exoplanets fall broadly into three classes: i) cool planets with homogeneous cloud coverage, ii) intermediate temperature planets with asymmetric dayside cloud coverage, and iii) ultra-hot planets without clouds on the dayside. In class ii),} the dayside cloud patterns are shaped by the wind flow and irradiation. Surface gravity and planetary rotation have little effect. Extended atmosphere profiles suggest the formation of mineral haze in form of metal-oxide clusters (e.g. (TiO2)_N). The dayside cloud coverage is the tell-tale sign for the different planetary regimes and their resulting weather and climate appearance. Class (i) is representative of planets with a very homogeneous cloud particle size and material compositions across the globe (e.g., HATS-6b, NGTS-1b), classes (ii, e.g., WASP-43b, HD\,209458b) and (iii, e.g., WASP-121b, WP0137b) have a large day/night divergence of the cloud properties. The C/O ratio is, hence, homogeneously affected in class (i), but asymmetrically in class (ii) and (iii). The atmospheres of class (i) and (ii) planets are little affected by thermal ionisation, but class (iii) planets exhibit a deep ionosphere on the dayside. Magnetic coupling will therefore affect different planets differently and will be more efficient on the more extended, cloud-free dayside.

The first JWST observations of hot Jupiters showed an unexpected detection of SO2 in their hydrogen-rich atmospheres. We investigate how much sulphur can be expected in the atmospheres of rocky exoplanets and which sulphur molecules can be expected to be most abundant and detectable by transmission spectroscopy. We run thermo-chemical equilibrium models at the crust-atmosphere interface, considering surface temperatures 500 to 5000 K, surface pressures 1 to 100 bar, and various sets of element abundances based on common rock compositions. Between 1000 K and 2000 K, we find gaseous sulphur concentrations of up to 25 percent above the rock in our models. SO2, SO, H2S and S2 are by far the most abundant sulphur molecules. SO2 shows potentially detectable features in transmission spectra at about 4 micron, between 7 and 8 micron, and beyond 15 micron. In contrast, the sometimes abundant H2S molecule is difficult to detect in these spectra, which are mostly dominated by H2O and CO2. Although the molecule PS only occurs with concentrations below 300 ppm, it can cause a strong absorption feature between 0.3 and 0.65 micron in some of our models for high surface pressures. The detection of sulphur molecules would enable a better characterisation of the planetary surface.

The deep atmosphere of Jupiter is obscured beneath thick clouds. This causes direct observations to be difficult, and thermochemical equilibrium models fill in the observational gaps. This research uses Galileo and Juno data together with the Gibbs free energy minimization code GGchem to update the gas phase and condensation equilibrium chemistry of the deep atmosphere of Jupiter down to 1000 bars. Specifically, the Galileo data provides helium abundances and, with the incorporated Juno data, we use new enrichment values for oxygen, nitrogen, carbon and sulphur. The temperature profile in Jupiter’s deep atmosphere is obtained following recent interior model calculations that fit the gravitational harmonics measured by Juno. Following this approach, we produced pressure–mixing ratio plots for H, He, C, N, O, Na, Mg, Si, P, S and K that give a complete chemical model of all species occurring to abundances down to a 10−20 mixing ratio. The influence of the increased elemental abundances can be directly seen in the concentration of the dominant carriers for each element: the mixing ratio of NH3 increased by a factor of 1.55 as compared with the previous literature, N2 by 5.89, H2O by 1.78, CH4 by 2.82 and H2S by 2.69. We investigate the influence of water enrichment values observed by Juno on these models and find that no liquid water clouds form at the oxygen enrichment measured by Galileo, EH2O = 0.47, while they do form at higher water abundance as measured by Juno. We update the mixing ratios of important gas phase species, such as NH3, H2O, CO, CH4 and H2S, and find that new gas phase species, such as CN−, (NaCN)2, S2O and K+, and new condensates, namely H3PO4 (s), LiCl (s), KCl (s), NaCl (s), NaF (s), MgO (s), Fe (s) and MnS (s), form in the atmosphere.

Context. Gaseous exoplanets are the targets that enable us to explore fundamentally our understanding of planetary physics and chemistry. With observational efforts moving from the discovery into the characterisation mode, systematic campaigns that cover large ranges of global stellar and planetary parameters will be needed to disentangle the diversity of exoplanets and their atmospheres that all are affected by their formation and evolutionary paths. Ideally, the spectral range includes the high-energy (ionisation) and the low-energy (phase-transitions) processes as they carry complementary information of the same object. Aims. We aim to uncover cloud formation trends and globally changing chemical regimes into which gas-giant exoplanets may fall due to the host star’s effect on the thermodynamic structure of their atmospheres. We aim to examine the emergence of an ionosphere as indicator for potentially asymmetric magnetic field effects on these atmospheres. We aim to provide input for exoplanet missions such as JWST, PLATO, and Ariel, as well as potential UV missions ARAGO, PolStar, or POLLUX on LUVOIR. Methods. Pre-calculated 3D GCMs for M, K, G, F host stars are the input for our kinetic cloud model for the formation of nucleation seeds, the growth to macroscopic cloud particles and their evaporation, gravitational settling, element conservation and gas chemistry. Results. Gaseous exoplanets fall broadly into three classes: i) cool planets with homogeneous cloud coverage, ii) intermediate temperature planets with asymmetric dayside cloud coverage, and iii) ultra-hot planets without clouds on the dayside. In class ii), the dayside cloud patterns are shaped by the wind flow and irradiation. Surface gravity and planetary rotation have little effect. For a given effective temperature, planets around K dwarfs are rotating faster compared to G dwarfs leading to larger cloud inhomogeneities in the fast rotating case. Extended atmosphere profiles suggest the formation of mineral haze in form of metal-oxide clusters (e.g. (TiO2)N). Conclusions. The dayside cloud coverage is the tell-tale sign for the different planetary regimes and their resulting weather and climate appearance. Class (i) is representative of planets with a very homogeneous cloud particle size and material compositions across the globe (e.g., HATS-6b, NGTS-1b), classes (ii, e.g., WASP-43b, HD 209458b) and (iii, e.g., WASP-121b, WP 0137b) have a large day-night divergence of the cloud properties. The C/O ratio is, hence, homogeneously affected in class (i), but asymmetrically in class (ii) and (iii). The atmospheres of class (i) and (ii) planets are little affected by thermal ionisation, but class (iii) planets exhibit a deep ionosphere on the dayside. Magnetic coupling will therefore affect different planets differently and will be more efficient on the more extended, cloud-free dayside. How the ionosphere connects atmospheric mass loss at the top of the atmosphere with deep atmospheric layers need to be investigated to coherently interpret high resolution observations of ultra-hot planets.

The initial abundance of radioactive heat producing isotopes in the interior of a terrestrial planet are important drivers of its thermal evolution and the related tectonics and possible evolution to an Earth-like habitat. The moderately volatile element K can be outgassed from a magma ocean into H$_2$-dominated primordial atmospheres of protoplanets with assumed masses between 0.55-1.0$ M_{\rm Earth}$ at the time when the gas disk evaporated. We estimate this outgassing and let these planets grow through impacts of depleted and non-depleted material that resembles the same $^{40}$K abundance of average carbonaceous chondrites until the growing protoplanets reach 1.0 $M_{\rm Earth}$. We examine different atmospheric compositions and, as a function of pressure and temperature, calculate the proportion of K by Gibbs Free Energy minimisation using the GGChem code. We find that for H$_2$-envelopes and for magma ocean surface temperatures that are $\ge$ 2500 K, no K condensates are thermally stable, so that outgassed $^{40}$K can populate the atmosphere to a great extent. However, due to magma ocean turn-over time and the limited diffusion of $^{40}$K into the upper atmosphere, from the entire $^{40}$K in the magma ocean only a fraction may be available for escaping into space. The escape rates of the primordial atmospheres and the dragged $^{40}$K are further simulated for different stellar EUV-activities with a multispecies hydrodynamic upper atmosphere evolution model. Our results lead to different abundances of heat producing elements within the fully grown planets which may give rise to different thermal and tectonic histories of terrestrial planets and their habitability conditions.

Context. The Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Échelle Spectrographs (CARMENES) instrument is searching for periodic radial-velocity (RV) variations of M dwarfs, which are induced by orbiting planets. However, there are other potential sources of such variations, including rotational modulation caused by stellar activity. Aims. We aim to investigate four M dwarfs (Ross 318, YZ CMi, TYC 3529-1437-1, and EV Lac) with different activity levels and spectral sub-types. Our goal is to compare the periodicities seen in 22 activity indicators and the stellar RVs, and to examine their stability over time. Methods. For each star, we calculated generalised Lomb-Scargle periodograms of pseudo-equivalent widths of chromospheric lines, indices of photospheric bands, the differential line width as a measure of the width of the average photospheric absorption line, the RV, the chromatic index that describes the wavelength dependence of the RV, and parameters of the cross-correlation function. We also calculated periodograms for subsets of the data and compared our results to TESS photometry. Results. We find the rotation periods of all four stars to manifest themselves in the RV and photospheric indicators, particularly the TiO 7050 index, whereas the chromospheric lines show clear signals only at lower activity levels. For EV Lac and TYC 3529-1437-1, we find episodes during which indicators vary with the rotation period, and episodes during which they vary with half the rotation period, similarly to photometric light curves. Conclusions. The changing periodicities reflect the evolution of stellar activity features on the stellar surface. We therefore conclude that our results not only emphasise the importance of carefully analysing indicators complementary to the RV in RV surveys, but they also suggest that it is also useful to search for signals in activity indicators in subsets of the dataset, because an activity signal that is present in the RV may not be visible in the activity indicators all the time, in particular for the most active stars.

Clouds are an integral part of planetary atmospheres, with most planets hosting clouds. The understanding of not only the formation, but also the composition of clouds is crucial to the understanding of future observations. As observations of the planet's surface will remain very difficult, it is essential to link the observable high atmosphere gas and cloud composition to the surface conditions. We present a fast and simple chemical equilibrium (eq.) model for the troposphere of rocky exoplanets, which is in chemical and phase eq. with the crust. The hydrostatic eq. atmosphere is built from bottom to top. In each atmospheric layer chemical eq. is solved and all thermally stable condensates are removed, depleting the atmosphere above in the effected elements. These removed condensates build an upper limit for cloud formation and can be separated into high and low temperature condensates. The most important cloud condensates for 1000K>T>400K are KCl, NaCl, FeS, FeS2, FeO, Fe2O3, Fe3O4. For T<400K H2O, C, NH3, NH4Cl, NH4SH are thermally stable. For even lower temperatures of T<150K CO2, CH4, NH3, H2S become stable. The inclusion of clouds with trace abundances results in the thermal stability of a total of 72 condensates for atmospheres with the different surface conditions (300K<T<1000K and p=1bar,100bar). The different cloud condensates are not independent of each other, but follow sequences of condensation, which are robust against changes in crust composition, surface pressure, and surface temperature. Independent of the existence of water as a crust condensate H2O is a thermally stable cloud condensate for all investigated elemental abundances. However, the water cloud base depends on the hydration level of the crust. Therefore, the detection of water condensates alone does not necessarily imply stable water on the surface, even if the temperature could allow water condensation.

Large planetesimals and planetary embryos ranging from several hundred to a few thousand kilometers can develop magma oceans through mutual collisions, gravitational energy, and the heating of short-lived radioactive elements. After the evaporation of the protoplanetary gas disk, one can divide such planetary embryos into two distinct populations. If they grow to a certain mass of about >0.5 MEarth before the dissipation of the disk, they will start to accrete a substantial primordial hydrogen-dominated atmosphere, while the gravitational potential of the smaller ones (≤0.5 MEarth) will be too low to support this type of primordial atmosphere. For the smaller planetary embryos, the initial magma ocean will subsequently solidify, and a steam atmosphere will be catastrophically outgassed that, if it does not condense, may be lost efficiently via hydrodynamic escape. The escaping H-atoms will further drag heavier trace elements like noble gases and outgassed moderately volatile elements (MVEs) such as K, Na, Si, and Mg into space. For the larger population of planetary embryos, however, the magma ocean below the primordial atmosphere will not solidify until most of the gaseous envelope will be lost, thereby providing favorable conditions for MVEs to be dissolved within such atmosphere. In our first study (Benedikt et al. 2020), we applied an upper atmosphere hydrodynamic escape model that includes the dragging of heavier species by escaping H-atoms and investigated atmospheric and elemental escape from planetary embryos between 1 MMoon and 1.5 MMars (that is, the population of small protoplanets that does not accrete a primordial hydrogen-dominated atmosphere) by assuming that the noble gases and MVEs mostly reside within the escaping atmosphere. Our results indicated that the steam atmospheres and the embedded trace elements will be lost efficiently before they condense for masses ≤0.5 MMars and orbital distances up to 1 AU. For heavier embryos of up to 1.5 MMars the atmosphere together with the trace elements can only be lost completely if a shallow magma ocean remains below the gaseous envelope which might be achieved through frequent impacts onto the planetary embryo. For embryos with masses ≤MMoon, on the other hand, the gravity is too weak for a dense atmosphere to build up against the high magma ocean related surface temperatures and all outgassed elements will escape immediately into space. The studied planetary embryos will, therefore, be severely depleted in noble gases and MVEs. In a follow-up study (Erkaev et al. 2022), we are currently focusing on the loss of the heat producing element 40K from initially bigger planetary embryos (that is, the population of protoplanets that was able to accrete a substantial primordial atmosphere). Contrary to our first study, we additionally applied equilibrium condensation models with the equilibrium chemistry GGCHEM code (Woitke et al. 2018) and found that for magma ocean surface temperatures of ≥2500 K no condensates that fix potassium are thermally stable, and 40K isotopes indeed populate such a primordial atmosphere to a great extent. By applying a sophisticated multispecies hydrodynamic upper atmosphere evolution model to study the loss of the atmosphere together with 40K, we found that depending on the initial size of the protoplanet and the early evolution of the host star, this process can indeed remove substantial amounts of 40K from protoplanetary bodies that are ≥0.5 MEarth. This effect alone can, together with the loss of MVEs from the smaller planetary embryos that serve as building blocks for the bigger ones, result in a wide variety of different potassium abundances at the fully grown planet. Since different abundances of heat producing elements have a significant influence onto the subsequent thermal and tectonic evolution of a planet, and therewith connected, on its tectonic modes (e.g., O’Neill et al. 2020), the process of early hydrodynamic escape of the heat producing isotope 40K can significantly impact the habitability, since not all rocky planets will end up with the "right" amount of heat production in its interior. However, this process cannot be viewed separately; other factors will additionally determine the initial heat budget of a planet such as collisional erosion, the feeding zone of the growing protoplanet or the initial composition of the protoplanetary disk. References: Benedikt, M.R., Scherf, M., Lammer, H., Marcq, E., Odert, P., Leitzinger, M., Erkev, N.V., Escape of rock-forming volatile elements and noble gases from planetary embryos, Icarus, 347, 113772, 2020. Erkaev, N.V., Scherf, M., Herbort, O., Lammer, H., Odert, P., Kubyshkina, D., Leitzinger, M., Woitke, P., O’Neill, C., Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres, Mon. Not. R. Ast. Soc., under revision, 2022. O’Neill, C., O’Neill, H.S.C., Jellinek, A.M., On the Distribution and Variation of Radioactive Heat Producing Elements Within Meteorites, the Earth, and Planets, Space Sci. Rev., 216, id.37, 2020. Woitke, P., C. Helling, Hunter, G.H., Millard, J.D., Turner, G.E., Worters, M., Blecic, J., Stock, J.W., Equilibrium chemistry down to 100 K. Impact of silicates and phyllosilicates on the carbon to oxygen ratio, Astron. Astrophys. 614, id.A1, 2018.

One of the fundamental questions for planetary science is how surfaces of other planets similar to the rocky bodies in our solar system look like. What is the rock structure like? Will there be water? Are there any active atmospheric cycles? How can these different conditions be detected? The current space missions and ground based instruments allow the detection of specific gas species and some cloud compositions in atmospheres of giant exoplanets. With instruments installed in the near future and space crafts currently being build or planned, these kind of observations will be available for planets with smaller sizes and an overall rocky composition. We aim to further understand the connection of the conditions of the upper atmosphere with the conditions on the crust of the planet (temperature, pressure, composition). Our equilibrium chemistry models allow us to investigate the expected crust and near-crust-atmosphere composition. With this, we investigate the conditions under which liquid water is actually stable at the surface of a planet and not incorporated in hydrated rocks. Based on this crust - near-crust-atmosphere interaction we build an atmospheric model, which allows us to investigate what kind of clouds are stable and could be present in atmospheres of rocky exoplanets. This allows us to predict what clouds on other planets could be made of. Potential detection of cloud condensates and the high altitude gas phase can constrain the overall surface conditions on those planets.