Instructions for Presenters

The poster boards are 37.5 inches (95 cm) tall and 48 inches wide (122 cm), approximately fitting A0-sized posters in landscape orientation. Printing posters locally in Oxford is possible through the Physics Media Services (pick-up in the Denys Wilkinson Building, a short walk from the conference site). Posters can stay in place throughout the week. Posters can be advertised to the entire audience by brief 1-min flash talks (see Programme). For this purpose please send a 1-slide summary to by 1 July. Poster flash talks will be ordered according to their arrival.

Titles & Abstracts

Pierre Auclair-Desrotour (IMCCE, Paris Observatory):

Meta-modelling the climate of synchronously rotating rocky planets

Rocky planets orbiting in the habitable zone of low-mass stars are likely to be tidally locked in 1:1 spin-orbit resonance. In this configuration, they exhibit permanent dayside and nightside, which induces a day-night temperature gradient. The resulting climate can be unstable and generate a runaway condensation of greenhouse gases on the nightside that is called atmospheric collapse. As a consequence, it is crucial to elucidate the mechanisms that govern the day-night heat redistribution on these planets to better constrain their surface conditions. In this talk, we present a hierarchical approach based on the slow rotator approximation that we call a General Circulation Meta-Model (GCMM), and that we developed as a first attempt to bridge the gap between multiple modelling approaches ranging from simplified analytical greenhouse models to sophisticated 3-D General Circulation Models (GCM). The model is able to reproduce both the closed-form solutions obtained in earlier studies, the numerical solutions obtained from GCM simulations, and solutions provided by intermediate models. We show that this approach can be efficiently used to characterise the atmospheric stability of Earth-sized rocky planets, and to disentangle the contributions of radiative transfer, atmospheric dynamics, and turbulent diffusion. Particularly, it suggests that the planetary boundary layer can play a significant role in determining the collapse pressure.

Marc Brouwers (University of Cambridge):

Prograde spin-up during gravitational collapse

Astrophysical objects on different scales appear to possess a preferential spin-orbit alignment, pointing to shared processes that tie their rotation at birth to larger parent structures. We present a new mechanism that describes how collections of particles or 'clouds' gain a prograde rotational component when they collapse or contract while subject to an external, central force. The effect is geometric in origin, as relative shear on curved orbits moves their shared center-of-mass slightly inward and toward the external potential during a collapse, exchanging orbital angular momentum into aligned (prograde) rotation. For clouds that form at the interface of shear and self-gravity, prograde spin-up means that even setups with large initial retrograde rotation collapse to form prograde-spinning objects. We highlight an application to the Solar System, where we suggest that prograde spin-up can explain the frequency of binary comets in the Kuiper belt with prograde rotation.

Ryan Boukrouche (University of Oxford):

Post-runaway climate state on rocky worlds with large water inventories

This talk will present recent results of compared 1D simulations of runaway greenhouse pure steam atmospheres, and explore ways that allows a planet to transition from the runaway greenhouse state to a post-runaway, potentially habitable climate state.

Erica Bisesi (Astronomical Observatory of Trieste - INAF):

Impact of climate on habitability of terrestrial-type exoplanets

The climate of a planet is of paramount importance to establish the possible presence of liquid water at its surface, and thus, in a wide sense generally accepted by the scientific community, its habitability. Climate depends on a high number of factors and parameters, both astrophysical (e.g., luminosity of the central star(s), distance of the planet from the star, orbital eccentricity) and planetary (inclination of the rotation axis, duration of the day, atmospheric composition and pressure, presence and fraction of oceans, presence and type of soil, orography, topography, etc.). Some of these parameters have been or will be measured in the near future; data on the others will not be available in short time, and maybe not even in the far future. Therefore simple, although approximate, climate models lend themselves to better serving at parameter space exploration (involving both well-known and unknown parameters) than the more complex Global Circulation Models (GCM), in reason of their much lower computational cost. “Simple” models allow running thousands of experiments at the same computational time of a single GCM's run. A representative example of such a streamlined model is ESTM (Earth-like Surface Temperature Model; Vladilo et al. 2013, 2015). ESTM is based on the numerical solution of a modified diffusion equation for the meridional heat transfer, coupled with a radiative-convective column atmospheric model to account for the vertical transport of radiation (downward and upward). ESTM has been used for studying a number of characteristics of possible exoplanets candidates (e.g., Silva et al. 2017). After calibration with Earth experimental data and validation with 3D climate models, ESTM has been exploited to compile more than 20,000 climate simulations of terrestrial-type planets, with the aim of understanding how variations of planetary quantities (i.e., orbital semi-major axis, eccentricity, obliquity of the rotation axis, surface geography, surface atmospheric pressure and CO2 partial pressure) not measurable with present observational techniques may affect the surface temperature and habitability of extrasolar planets (the ARTECS archive of terrestrial-type climate numerical simulations; Murante et al. 2020). Another well-known regulator of a planet’s climate is its vegetation cover. Vegetation can modify the planetary surface albedo, being usually darker than the bare surface of the continents, an effect known as the “Charney mechanism” (Charney 1975, Baudena et al. 2008, Cresto Aleina et al. 2013). Here, ESTM has been exploited to investigate the impact of the Charney mechanism on an exoplanet’s habitability. We are currently applying the newly developed, vegetation-switched-on version of ESTM to study the circumstellar habitable zone and exoplanets’ habitability (Bisesi et al., in preparation). We are investigating how different and competing vegetation types (that resemble trees, grasslands and tree seedlings) may reach equilibrium distribution on a planet depending on its main properties (the most straightforward of these being the insolation, i.e., a combination of stellar luminosity and planet distance from the star). As different equilibrium states correspond to a different planetary surface albedo, we are estimating how vegetation can extend the planet’s circumstellar habitable zone beyond its external border as a consequence of a decrease in surface albedo. In special cases known as “waterbelt” – e.g., planets almost completely covered by ice, except for a narrow band near the equator – plants could also heat up the planet, thus enlarging the liquid water band and extending the overall habitability fraction. By combing results of such simulations from the ARTECS database with the concept of GHZ (cf. Lineweaver et al. 2004; Spitoni et al. 2017) and a generalized mathematical/computational approach for estimating the probabilities of transitions and expectations for biological evolution (Bisesi and Ferluga, under submission), we finally aim at identifying which part of the Galaxy may host a fully-compatible biosphere for the development of complex life.

Andrew Buchan (Institute of Astronomy, University of Cambridge):

Planets or asteroids? How geochemistry constrains the masses of White Dwarf pollutants

Polluted white dwarfs that have accreted planetary material provide a unique opportunity to probe the interiors of exoplanetary bodies. The compositions of such bodies encode information about their formation histories, including the geological process of core-mantle differentiation, with wide ranging implications for habitability. However, the nature of the bodies which pollute white dwarfs is not well understood: are they small asteroids, minor planets, or even terrestrial planets?

In our work, we present a novel method to infer pollutant masses from detections of Ni, Cr and Si. These elements exhibit variable preference for metal and silicate during core-mantle differentiation, depending on the conditions under which it occurs. This alters their relative abundance in the core and mantle of differentiated bodies, and in turn the composition of any fragments derived from these bodies. The pressure inside the body is a key parameter, and depends on the body’s mass.

By modelling core-mantle differentiation self-consistently using data from metal--silicate partitioning experiments, we place statistical constraints on the differentiation pressures (and hence masses) of bodies which pollute white dwarfs. We find 3 systems whose abundances are best explained by the accretion of fragments of small parent bodies, and 2 systems which imply accretion of fragments of Earth-sized bodies. This provides evidence for the presence of core-mantle differentiated bodies of a range of masses in exoplanetary systems.

Richard Chatterjee (University of Oxford):

Time-dependent simulation of hydrodynamic escape of planetary atmospheres

The solution of steady-state transonic planetary winds driven by stellar irradiation is a two-point boundary-value problem (BVP). The first numerical attempts used the shooting method, where the solution is found by trial-and-error and has applicability limited by its sensitivity (Watson 1981). Later, this was improved upon with the development of a relaxation method (Murray-Clay 2009) but in this you still have to guess a trial solution. It has now become clear that using an initial-value problem (IVP) approach and time-stepping the full hydrodynamic equations is the most effective solution method. The was first implemented for a terrestrial planet by Tian (2005); this was then improved on by Kuramoto (2013), and since then a range of models have been developed (e.g. Caldiroli 2021). However, not much attention has been paid to actual time evolution, either as a path to steady state or as a response to time-dependent forcing. I will present some new insights from time-dependent simulations using the CIP and CIP-CSL2 schemes (Yabe 1991, 2001); emphasising the role of viscosity in particular.

Swastik Chowbay (Indian Institute of Astrophysics):

Galactic chemical evolution of exoplanet hosting stars: Are high-mass planetary systems young?

The imprints of stellar nucleosynthesis and chemical evolution of the galaxy can be seen in different stellar populations, with older generation stars showing higher α-element abundances while the later generations becoming enriched with iron-peak elements. The evolutionary connections and chemical characteristics of circumstellar disks, stars, and their planetary companions can be inferred by studying the interdependence of planetary and host star properties. Numerous studies in the past have confirmed that high-mass giant planets are commonly found around metal-rich stars, while the stellar hosts of low-mass planets have a wide range of metallicity. In this work, we analyzed the detailed chemical abundances for a sample of >900 exoplanet hosting stars drawn from different radial velocity and transit surveys. We correlate the stellar abundance trends for α and iron-peak elements with the planets' mass. We find the planet mass-abundance correlation to be primarily negative for α-elements and marginally positive or zero for the iron-peak elements, indicating that stars hosting giant planets are relatively younger. This is further validated by the age of the host stars obtained from isochrone fitting. The later enrichment of protoplanetary material with iron and iron-peak elements is also consistent with the formation of the giant planets via the core accretion process. A higher metal fraction in the protoplanetary disk is conducive to rapid core growth, thus providing a plausible route for the formation of giant planets. This study, therefore, indicates the observed trends in stellar abundances and planet mass are most likely a natural consequence of Galactic chemical evolution.

Collin Cherubim (Harvard University):

Isotopic fractionation as a way to infer exoplanet atmospheric evolution pathways

Measurements of exoplanet radius and atmospheric isotopic fractionation offer a potential means to probe atmospheric evolution and to better constrain competing formation mechanisms. We are developing a numerical model that computes fractionation caused by atmospheric loss, with an initial focus on deuterium to hydrogen (D/H) enhancement on sub-Neptunes. Using mass-radius relations derived from thermal evolution models, we postdict initial atmospheric mass fraction and isotope enhancement by comparing present-day radius estimates to model predictions based on a specified escape pathway. Our preliminary results suggest that the degree of fractionation is sensitive to both the type of escape process and the planet’s initial H2 inventory. We are currently investigating the degree to which various fractionation patterns can be constrained from transmission spectroscopy.

Jessica Cmiel (Harvard University): Volatile Partitioning on Early Venus

Magma oceans play a crucial role in establishing the initial conditions for different evolutionary paths of terrestrial planet atmospheres. The speciation of volatiles between a planet’s magma ocean and atmosphere is dependent on effects such as chemical solubility and redox state, as characterized by the oxygen fugacity (ƒO2) of the magma. This in turn has important implications for an emerging planet’s atmospheric composition. We are developing a new coupled model that incorporates volatile partitioning and oxygen fugacity changes in a terrestrial planet with a magma ocean. We are using this model to to understand how hydrodynamic H escape and other redox-varying processes influenced the chemical partitioning of volatile species on early Venus. Our ultimate aim is to constrain the range of possible initial atmospheric compositions on Venus to understand how its early climate may have evolved relative to Earth’s.

Alfred Curry (Imperial College London):

Investigating rocky interiors by modelling disintegrating exoplanets

Vera Dobos (Kapteyn Astronomical Institute, University of Groningen):

A target list for searching habitable exomoons

Although there are no confirmed exomoon discoveries to date, their potential habitability is an important question. Extending the search for life to exomoons expands our possibilities and chances to find habitable environments outside the Solar System. Detecting the first habitable exomoon will provide great opportunities to study and characterize this new type of extra-solar body. In this talk I will present our latest work which provides a target list for observing exoplanets which can host large, habitable moons on stable orbits. To determine their habitability, we calculated the incident stellar radiation and the tidal heating flux arising in the moons as the two main contributors to the energy budget. We used the runaway greenhouse and the maximum greenhouse flux limits as a definition of habitability. For each exoplanet we ran our calculations for plausible ranges of physical and orbital parameters for the moons and the planet using a Monte Carlo approach. Two promising candidates in our list are Kepler-62 f and Kepler-16 b, both of them with known masses and radii. Our target list can help to detect the first habitable exomoon.

Jingyao Dou (University of Bristol):

Giant impact benchmark tests between GADGET2 and SWIFT

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian particle-based method that has been widely used to study giant impacts, where planets are modelled with particles that evolve under gravity and material pressure. SWIFT is a recently developed hydrodynamics and gravity code for astrophysics and cosmology which can be used as a drop-in replacement for GADGET-2 and is reported to have a faster runtime on representative cosmological problems. We compared the performance and results of the two codes in terms of planetary giant impact simulations and found that the run time and simulation results of SWIFT will greatly depend on the maximum smoothing length set in the code. Given proper maximum smoothing length, SWIFT could run giant impact simulations faster than that of the GADGET-2 while the final results of the two codes were similar. We are currently using SWIFT to study the erosion of a protoplanet's atmosphere during a giant impact when there is an ocean at the surface of the planet.

Vanessa Emeka-Okafor (University of Warwick)

Namrah Habib (University of Oxford):

Modelling Dry Compositional Convection for Applications to Terrestrial Exoplanets

Mark Hammond (University of Oxford):

The Overturning Circulation and Day-Night Temperature Contrast on Tidally Locked Rocky Planets

Tidally locked planets always present the same side to their host star. The difference in temperature between their permanent day-side and permanent night-side is a key contributor to their habitability and atmospheric stability. It also plays a key role in observations of atmospheric composition and temperature structure. We show that on a planet with an atmosphere, this temperature difference is almost entirely governed by one component of the atmospheric circulation -- the overturning circulation. We derive a predictive model of this circulation and compare its predicted day-night temperature contrast to simulations in 3D atmospheric models.

Dongyang Huang (ETH Zurich):

Nitrogen speciation in a terrestrial magma ocean and an N-enriched secondary atmosphere

Rolf Kuiper (University of Duisburg-Essen):

The Recycling Hypothesis in the Formation of Proto-planet's first Atmospheres

In the core accretion paradigm of planet formation, gas giants form a massive atmosphere in a run-away gas accretion phase once their progenitors exceed a threshold mass: the critical core mass. On the one hand, the majority of observed exo-planets, being smaller and rock/ice-dominated, never crossed this line. On the other hand, these exo-planets have accreted substantial amounts of gas from the circumstellar disk during their embedded formation epoch.

We investigate the hydrodynamical and thermodynamical properties of proto-planetary atmospheres by direct numerical modeling of their formation epoch. Our studies cover one-dimensional (1D) spherically symmetric, two-dimensional (2D) axially symmetric, and three-dimensional (3D) hydrodynamical simulations with and without radiation transport. We check the feasibility of different numerical grid geometries (Cartesian vs. spherical), perform convergence studies, and scan the physical parameter space with respect to planet mass and optical depth of the surrounding.

In terms of hydrodynamic evolution, no clear boundary demarcates bound atmospheric gas from disk material in a 3D scenario in contrast to 1D and 2D computations. Atmospheres denote open systems where gas enters and leaves the Bondi /Hill sphere in both directions. In terms of thermodynamics, we compare the gravitational contraction of the forming atmospheres with its radiative cooling and hydrodynamical advection of energy, as well as the interplay of these processes. The coaction of radiative cooling of atmospheric gas and advection of atmospheric-disk gas prevents the proto-planets to undergo run-away gas accretion. Hence, this recycling process provides a natural explanation for the preponderance of super-Earth like planets.

To advertise the general purpose approach of our code development, I will also briefly overview the most recent results obtained in a variety of other astrophysical research fields from proto-planets on supersonic, eccentric orbits (Mai et al. 2020), to accretion and multiplicity in massive star formation (Oliva & Kuiper 2020), up to the formation of the progenitors of the first supermassive black holes in the early universe (Hirano et al. 2017, Science).

Matt Lodge (University of Bristol):

Scattering from Non-Spherical Aerosol Aggregates in Exoplanet Atmospheres

The majority of atmospheric scattering models assume spherical particles to allow fast computation of their optical parameters. However, evidence from atmospheric studies on Earth suggests particles often display more complex geometries, for example exhibiting fractal structures with distinct monomers. This research aims to explore the consequences on the optical properties of non-spherical aerosols, and in particular, the consequences for modelling the transmission spectra of exoplanet atmospheres.

Erik Meier (Center for Space and Habitability, University of Bern):

Variable occultation depth of 55 Cnc e in the visible range

Among the numerous super-Earths discovered so far, 55 Cnc e presents itself as one of the most mysterious exoplanets. It has been observed that the occultation depth of the planet, with an orbital period of 0.73 days, changes significantly over time at mid-infrared wavelengths. Observations with Spitzer measured a change in its day-side brightness temperature of 1200 K, possibly driven by volcanic activity, magnetic star-planet interaction, or the presence of a circumstellar torus of dust. Here we present that the variability exists also in the optical.

TESS observed 55 Cnc during sectors 21, 44 and 46. We report an occultation depth of 8±2.5 ppm for the complete set of TESS observations. In particular, we measured a depth of 15±4 ppm for sector 21, while for sector 44 we detect no occultation. In sector 46 we measure a weak occultation of 8±5 ppm. The occultation depth varies from one sector to the next between 1.6 and 3.4 σ significance. We also derived the possible contribution on reflected light and thermal emission, setting an upper limit on the geometric albedo.

Based on a model comparison between varying occultation across sectors, a constant occultation and no occultation at all, the presence of an occultation is favoured considerably over no occultation, where the model with varying occultation across sectors takes most of the statistical weight.

Our analysis confirms a detection of the occultation in TESS. Moreover, our results weakly lean towards a varying occultation depth between each sector. The process responsible for this phenomenon is still unknown, but future missions, such as JWST, might provide the key pieces to this puzzling system.

Juliana García-Mejía (Harvard University):

First Light Results from the Tierras Observatory, An Ultra-precise Time-series M-dwarf Photometer

We are engaged in a project to refashion the 1.3m 2MASS telescope located at the F.L. Whipple Observatory atop Mount Hopkins, Arizona, into an ultra-precise time-series photometer: The Tierras Observatory is designed to achieve a photometric precision of 250 ppm across an observing season. The design choices that enable this precision include a four-lens focal reducer and field-flattener to increase the field-of-view of the telescope from 12 arc minutes to 0.48 degrees on a side; a custom narrow (40 nm) bandpass filter centered around 863.5 nm to minimize precipitable water vapor errors known to limit ground-based photometry of M dwarfs; a deep-depletion 4k x 4k CCD with a quantum efficiency of 85% in our bandpass, operating in frame transfer mode; and, a fully automated observing mode. Tierras achieved first light in the fall of 2021, and in February 2022 we installed a new set of baffles to significantly reduce sky background. We will share recent light curves and summarize our current on-sky performance. Tierras is starting a three-year survey of M dwarf stars within 15 parsecs to detect new terrestrial planets that were too small or too cool to be found by TESS or previous ground-based efforts, and to monitor known exoplanets (both rocky and gaseous) to search for satellites or systems of circumstellar rings. Furthermore, a long term monitoring campaign will permit Tierras to determine M dwarf rotation periods, elucidating the process and timescale over which these stars lose their angular momentum.

Claire Guimond (University of Cambridge):

Limits to land planets, and how to store oceans on or inside them

Do we expect many rocky planets to have both oceans and dry land? Directly detecting exoplanet surfaces will be at the least extremely difficult, yet this information is key to interpreting climate models and biosignatures. Whilst Earth's marbled appearance seems to have emerged from complex, entwined systems, one imagines multiple ways to create the same effect on planets in different geodynamic regimes. We take first steps towards estimating the frequency of extrasolar blue marbles by modelling the simplest processes that set planetary land/ocean fractions. On one hand, topography increases land propensity by hollowing out ocean basins, storing surface water. To this end we quantify how dynamic topography---surface undulations caused by upwelling mantle---scales with constrainable bulk planet properties. Such scalings can tell us the minimum (pessimistic) ocean mass that would flood a planet. On the other hand, a higher total water budget will push a planet towards a fully water-covered regime. We expect planetary mantles to be a large reservoir for water (i.e., hydrogen stored in minerals), which over time supplies the surface via outgassing. Thus we also preliminarily estimate maximum mantle water capacities as a function of stellar-derived mineralogy. Together, limits on topography and on water budgets present two uses of deterministic geophysical modelling towards understanding aspects of rocky worlds not accessible to observation.

Sean Jordan (Institute of Astronomy, University of Cambridge):

Metabolic Signatures of an Aerial Biosphere in the Clouds of Venus

Life in the clouds of Venus, if present in sufficiently high abundance, must be affecting the atmospheric chemistry. It has been proposed that abundant Venusian life could obtain energy from its environment using three possible sulfur-based metabolisms. These metabolisms raise the possibility of Venus's enigmatic cloud-layer SO2-depletion being caused by life. We couple each metabolic pathway to a photochemical-kinetics model and self-consistently predict the composition of Venus's atmosphere under the scenario that life produces the observed SO2-depletion. Using this photo-bio-chemical kinetics model, we show that all three metabolisms can produce SO2-depletions, but do so by violating other observational constraints on Venus's atmospheric chemistry. We calculate the maximum possible biomass density of sulfur-metabolising life in the clouds, before violating observational constraints, to be ~ 10^-5 - 10^-3 mg m-3. The methods employed are equally applicable to aerial biospheres on Venus-like exoplanets, planets that are optimally poised for atmospheric characterisation in the near future.

Giuseppe Murante (INAF-Trieste Observatory):

Climate bistability of Earth-like exoplanets

Before about 500 million years ago, most probably our planet experienced temporary snowball conditions, with continental and sea ices covering a large fraction of its surface. This points to a potential bistability of Earth's climate that can have at least two different (statistical) equilibrium states for the same external forcing (I.e. solar radiation). Here, I will explore the probability of finding bistable climates in Earth-like exoplanets and consider the properties of planetary climates obtained by varying the semimajor orbital axis (thus, received stellar radiation), eccentricity and obliquity, and atmospheric pressure. To this goal, we used the Earth-like planet surface temperature model (ESTM), an extension of one-dimensional Energy Balance Models developed to provide a numerically efficient climate estimator for parameter sensitivity studies and long climatic simulations. I will shortly describe out model. After verifying that the ESTM is able to reproduce Earth climate bistability, we identify the range of parameter space where climate bistability is detected. An intriguing result of this work is that the planetary conditions that support climate bistability are remarkably similar to those required for the sustenance of complex, multicellular life on the planetary surface. The interpretation of this result deserves further investigation, given its relevance for the potential distribution of life in exoplanetary systems.

Claire Nichols (Department of Earth Sciences, University of Oxford):

A Time-Resolved Paleomagnetic Record of Main Group Pallasites: Evidence for a Large-Cored, Thin-Mantled Parent Body

Several paleomagnetic studies have been conducted on five Main Group pallasites: Brenham, Marjalahti, Springwater, Imilac, and Esquel. These pallasites have distinct cooling histories, meaning that their paleomagnetic records may have been acquired at different times during the thermal evolution of their parent body. Here, we compile new and existing data to present the most complete time- resolved paleomagnetic record for a planetesimal, which includes a period of quiescence prior to core solidification as well as dynamo activity generated by compositional convection during core solidification. We present new paleomagnetic data for the Springwater pallasite, which constrains the timing of core solidification. Our results suggest that in order to generate the observed strong paleointensities (∼65–95 μT), the pallasites must have been relatively close to the dynamo source. Our thermal and dynamo models predict that the Main Group pallasites originate from a planetesimal with a large core (>200 km) and a thin mantle (<70 km).

Anjali Piette (Carnegie Earth & Planets Laboratory):

Atmospheric Retrieval of Rocky Exoplanets in Thermal Emission

Emission spectroscopy is a promising technique to observe atmospheres of rocky exoplanets, probing both their chemistry and thermal profiles. I will present HyDRo, an atmospheric retrieval framework for thermal emission spectra of rocky exoplanets. HyDRo does not make prior assumptions about the background atmospheric composition, and can therefore be used to interpret spectra of secondary atmospheres with unknown compositions. I will further show how HyDRo can be used to assess the chemical constraints which can be placed on rocky exoplanet atmospheres using JWST. I identify the best currently-known rocky exoplanet candidates for spectroscopic observations in thermal emission with JWST, finding >30 known planets whose thermal emission will be detectable by JWST/MIRI in fewer than 10 eclipses at R~10. I then consider the observations required to characterise the atmospheres of three promising rocky exoplanets across the ~400-800K equilibrium temperature range: Trappist-1b, GJ1132b, and LHS3844b. Considering a range of CO2- to H2O-rich atmospheric compositions, I find that CO2 and H2O can be detected in these atmospheres with reasonable amounts of JWST observing time, and that their abundances can be constrained with good precision. Finally, I will discuss the impact of clouds on emission spectra of rocky exoplanets and on their atmospheric retrievals. HyDRo will allow important atmospheric constraints on rocky exoplanets with JWST observations, providing crucial insights into their geochemical environments.

David Rice (University of Nevada, Las Vegas):

Investigating systematic uncertainties in terrestrial interior models with MAGRATHEA

The community uses a variety of models to characterize the interior structure of small planets. Underlying these models are multiple computational techniques, numerous experimental measurements and theoretical estimates of the equations of state for planet-building materials, and differing treatments of temperature. MAGRATHEA is an open-source interior structure solver which can be customized to user-defined planet models. Our code features adaptable phase diagrams for the core, mantle, hydrosphere, and atmosphere and transparent storage for equations of state. I will demonstrate how the community can use and contribute to the code. I then use MAGRATHEA to test model parameters and quantify systematic uncertainties in the characterization of small planets such as those in the Trappist-1, K2-138, and K2-146 systems.

Robert Ridgway (University of Exeter):

3D Modelling of the Impact of Stellar Flares on Earth-like Rocky Planets Orbiting M Dwarf Stars

The current best candidates for habitable exoplanets have been detected orbiting M-dwarf stars. Such stars are quite common, and their low brightness and the short orbital periods of their planets both aid observations. Many M dwarf stars are known to produce stellar flares, phenomena where the star releases substantial amounts of energy, particularly in the ultraviolet (UV) and becomes much brighter for a period of minutes to hours. In addition, flares are associated with a release of energetic protons from the star, known as stellar proton events. Flares released by the Sun are less energetic than those of M dwarfs. This presents some questions about the habitability of exoplanets around M dwarfs. The increased UV light and the protons may induce long-term changes in the exoplanetary atmosphere by destroying molecules such as ozone that help shield the surface from the UV. This would make the planet’s surface dangerous for terrestrial life and may make the emergence and survival of surface-based life impossible. I present results from a study in 3D using the UK Met Office global circulation model, termed the Unified Model (UM). The UM has been adapted to model a wide range of exoplanets. I present the results from simulations including a coupled chemical kinetics and photolysis scheme. Our chemical network describes the production of ozone via the Chapman cycle as well as the change in ozone due to HOx and NOx photochemistry. A tidally locked aquaplanet with an Earth-like atmosphere is simulated for twenty years under quiescent conditions before it is subjected to a series of flares of varying total energies drawn from a realistic distribution. I will describe the changes in the atmospheric composition as well as surface habitability that occur due to the flares.

Suman Saha (Indian Institute of Astrophysics):

Detection and Characterization of Habitable Exomoons

Rocky exomoons in the habitable zones of the exoplanetary systems hold special significance as they can host life. Although the detection of exomoons has yet remained elusive, mainly due to their smaller expected size, the next generation space missions such as JWST can provide unique opportunity for such detection. In this talk, I will present a comprehensive analytical formalism in order to model the lightcurves of transiting exoplanets hosting exomoons. In order to achieve an analytical formalism, we have considered circular orbit for the exomoon around the host planet, which is indeed the case for tidally locked moons. The formalism takes care of the co-alignement or non-coalignment of the orbits of the planet and the moon using a two angular parameter approach and can be used to model and characterize all the possible orbital alignments for a star-planet-moon system. Using this formulation, we have studied the detectability of rocky exomoons using next generation telescopes, such as JWST. We have also studied the observational limits on the characterization of the atmospheres of such exomoons using JWST.

Joseph Schulze (Ohio State University):

Uncertain planets: determining how precisely we can know rocky planet composition given equation of state limitations

The most fundamental inputs of rocky planet structure models, used to build mass-radius relationships and infer composition, are the underlying material-dependent equations of state (EOS) of core and mantle minerals. Such models often assume idealized compositions, neglect EOS uncertainties when extrapolating, and ignore EOS-to-EOS discrepancies, or use EsOS based on biased data. Separately, these effects can lead to model-dependent planet densities that vary by 1-10% over the observed rocky planet mass range. Several probable rocky planets now have density characterization to better than or near 10% uncertainty, meaning we are we are fast approaching an era where EOS uncertainty and variability must be carefully considered. Failing to do so will yield erroneously precise compositions which, in turn, may over-constrain planet formation/evolution models. Here, I quantify how precisely we can know super-Earth interiors given EOS uncertainty/variability and make material-specific EOS recommendations based on best practices in mineral physics. I combine my results with observational uncertainties into an open-source structure model for calculating the exact compositional uncertainties of rocky planets.

Marie-Luise Steinmeyer (GLOBE Institute, University of Copenhagen):

Envelopes around rocky planets during pebble accretion

The process of pebble accretion forms planets during the lifetime of the protoplanetary disks. These protoplanets are thus able to acquire gas envelopes during their growth period. Due to accretion heating, the temperature in the envelope can become high for pebbles to sublimate before they reach the embryo. At the same time, there exist recycling gas flows between the planetary envelope and the surrounding disk. Understanding the evolution of the gas envelopes and the sublimated pebbles is therefore key to understanding the composition protoplanet.

I present nested-grid, high-resolution 3D hydrodynamic simulations of pebble accretion on rocky protoplanets using the Dispatch framework (Nordlund et al., 2018; Popovas et al., 2018). The simulations extend down to the planetary surface. Therefore, my work is able to resolve the gas motion close a protoplanet during pebble accretion. I introduced gas tracers to the setup in order to study this motion in more detail. In addition, I present 1D models of these envelopes around low mass protoplanets to study the location of the sublimation fronts of different solids.

In the adiabatic limit, the recycling flow penetrates the Hill sphere of rocky protoplanets. Inside the Bondi sphere, the gas is bound to the planet. The 1D models including radiative transfer show a two-layer envelope with an inner convective and an outer radiative region. The sublimation fronts are located deep in convection region of the protoplanets.

Christiaan Van Buchem (Leiden University):

Modeling silicate atmospheres on hot rocky exoplanets

Hot rocky exoplanets with equilibrium temperatures above ∼2000 K (e.g. 55 Cnc e, K2-141 b, and GJ 367 b) are thought that have molten surfaces. This implies that there is a direct interface between the planet’s lava ocean and atmosphere. Hence, the composition of these planet’s atmospheres is likely to be closely linked to the composition of their lava oceans. This provides a unique opportunity for astronomers to characterize the mantle composition of such planets based on the composition of their atmospheres. With the recent launch of JWST and the future prospect of ARIEL ushering in a new era of exoplanet observations, this topic is now more relevant than ever.

In order to accomplish this, we must first gain a deeper understanding of the way in which a lava ocean interacts with an atmosphere. The first step in this process is to model the outgassing that takes place in a silicate melt. Using the thermodynamic data of the magma ocean provided by the MELTS code, we developed an open source code that predicts the composition of such a vaporised atmosphere for a given magma composition and temperature. In this poster we will present out methods, results, validation with lab data, and comparison to other similar codes.

The successful development of this method and subsequent comparisons to observations would allow us to start characterising rocky exoplanet compositions based on their atmo- sphere compositions, which could lead to new insights for formation models. Furthermore, it would also allow us to model the effects of transient magma oceans though to be present on young earth analogs. Deepening our understanding of how such processes influence the conditions present during later evolutionary stages and possibly give us new insights in the conditions necessary to sustain life.

Iris van Zelst (Institute of Planetary Research, German Aerospace Center):

Towards interior-atmosphere coupling on Venus

The evolution of the atmospheric composition of a planet is largely determined by the partial melting and volcanic outgassing of the interior. In turn, the composition of the atmosphere dictates the surface temperature of the planet (due to processes like the greenhouse effect), which is an important boundary condition for crustal and mantle processes in the interior of a planet. Venus in particular has a large atmosphere with an abundance of the greenhouse gas CO2 and a small amount of water vapour, which can significantly change the surface temperature and hence global mantle evolution of Venus. Since much of Venus’ evolution still remains elusive, we aim to study the coupled interior-atmosphere evolution of Venus to shed new light on Earth’s twin.

Here, we show the first results of coupling a grey atmosphere model (i.e., we assume that the absorption coefficients are constant and hence independent of frequency) considering only CO2 and H2O as greenhouse gases to the geodynamic code Gaia. We compare to previous studies who employed similar coupled models (e.g., Noack et al., 2012; Gillmann & Tackley, 2014; Höning et al., 2021). We also speculate how we could further expand the coupled atmospheric model to account for other chemical species such as sulfur and nitrogen.

Andrew Walker (Department of Earth Sciences, University of Oxford):

Non-equilibrium snow zones in planetary cores built from growing and sinking iron crystals

We describe a model of the formation of iron snow zones in planetary cores which have implications for the long timescale thermal evolution of planets and on the generation of an internal magnetic field. These two-phase snow zones are composed of a mixture of light-element enriched liquid and a small fraction of solid iron crystals. In contrast to most previous descriptions, we focus on modelling the physics controlling the growth and sinking of individual iron crystals and do not assume that the snow layer is in phase equilibrium. This means that our model does not require the temperature and solid volume to be linked through a liquidus relation and yields a distribution of solid grain sizes throughout the layer.

We consider the layer as a liquid iron-oxygen alloy cooled below the liquidus temperature such that microscopic solid iron crystals can form. Each crystal sinks because it is denser than the surrounding liquid. As the crystal sinks it also grows because of the chemical potential difference between iron in the solid and liquid phases. Growing crystals reject oxygen, moving the system towards equilibrium, but this equilibration is limited by the intrinsic growth kinetics of iron and by the need for iron to diffuse through an oxygen enriched boundary layer around the falling crystal. We model the layer as a collection of independently falling crystals which form throughout the layer and only interact by changing the composition of the liquid. Assuming the layer is in steady state and imposing the crystal formation rate, the temperature, and the overall composition, allows us to solve for the volume fraction of solid in the layer, the composition of the liquid, the size distribution of crystals, and, for deep snow zones, the growth rate of the planet's inner core.