arXiv subjects

João M. Mendonça

Publications and source records attributed to João M. Mendonça.

At least 37 records · Page 2Linked to original sources

arXiv2024

Global Chemical Transport on Hot Jupiters: Insights from 2D VULCAN photochemical model

The atmospheric dynamics of tidally-locked hot Jupiters is characterized by strong equatorial winds. Understanding the interaction between global circulation and chemistry is crucial in atmospheric studies and interpreting observations. Two-dimensional (2D) photochemical transport models shed light on how the atmospheric composition depends on circulation. In this paper, we introduce the 2D photochemical (horizontal and vertical) transport model, VULCAN 2D, which improves on the pseudo-2D approaches by allowing for non-uniform zonal winds. We extensively validate our VULCAN 2D with analytical solutions and benchmark comparisons. Applications to HD 189733 b and HD 209458 b reveal a transition in mixing regimes: horizontal transport predominates below $\sim$0.1 mbar while vertical mixing is more important at higher altitudes above 0.1 mbar. Motivated by the previously inferred carbon-rich atmosphere, we find that HD 209458 b with super-solar carbon-to-oxygen ratio (C/O) exhibits pronounced C$_2$H$_4$ absorption on the morning limb but not on the evening limb, owing to horizontal transport from the nightside. We discuss when a pseudo-2D approach is a valid assumption and its inherent limitations. Finally, we demonstrate the effect of horizontal transport in transmission observations and its impact on the morning-evening limb asymmetry with synthetic spectra, highlighting the need to consider global transport when interpreting exoplanet atmospheres.

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arXiv2024

Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b

Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5-12 $μ$m with JWST's Mid-Infrared Instrument (MIRI). The spectra reveal a large day-night temperature contrast (with average brightness temperatures of 1524$\pm$35 and 863$\pm$23 Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2$σ$ upper limit of 1-6 parts per million, depending on model assumptions).

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arXiv2023

Transmission spectroscopy of the lowest-density gas giant: metals and a potential extended outflow in HAT-P-67b

Extremely low-density exoplanets are tantalizing targets for atmospheric characterization because of their promisingly large signals in transmission spectroscopy. We present the first analysis of the atmosphere of the lowest-density gas giant currently known, HAT-P-67 b. This inflated Saturn-mass exoplanet sits at the boundary between hot and ultrahot gas giants, where thermal dissociation of molecules begins to dominate atmospheric composition. We observed a transit of HAT-P-67 b at high spectral resolution with CARMENES and searched for atomic and molecular species using cross-correlation and likelihood mapping. Furthermore, we explored potential atmospheric escape by targeting H$α$ and the metastable helium line. We detect Ca II and Na I with significances of 13.2$σ$ and 4.6$σ$, respectively. Unlike in several ultrahot Jupiters, we do not measure a day-to-night wind. The large line depths of Ca II suggest that the upper atmosphere may be more ionized than models predict. We detect strong variability in H$α$ and the helium triplet during the observations. These signals suggest the possible presence of an extended planetary outflow that causes an early ingress and late egress. In the averaged transmission spectrum, we measure redshifted absorption at the $\sim 3.8\%$ and $\sim 4.5\%$ level in the H$α$ and He I triplet lines, respectively. From an isothermal Parker wind model, we derive a mass loss rate of $\dot{M} \sim 10^{13}~\rm{g/s}$ and an outflow temperature of $T \sim 9900~\rm{K}$. However, due to the lack of a longer out-of-transit baseline in our data, additional observations are needed to rule out stellar variability as the source of the H$α$ and He signals.

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arXiv2023

Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab

Nearby M dwarf systems currently offer the most favorable opportunities for spectroscopic investigations of terrestrial exoplanet atmospheres. The LTT~1445 system is a hierarchical triple of M dwarfs with two known planets orbiting the primary star, LTT~1445A. We observe four transits of the terrestrial world LTT~1445Ab ($R=1.3$ R$_\oplus$, $M=2.9$ M$_\oplus$) at low resolution with Magellan II/LDSS3C. We use the combined flux of the LTT~1445BC pair as a comparison star, marking the first time that an M dwarf is used to remove telluric variability from time-series observations of another M dwarf. We find H$α$ in emission from both LTT~1445B and C, as well as a flare in one of the data sets from LTT~1445C. These contaminated data are removed from the analysis. We construct a broadband transit light curve of LTT~1445Ab from 620--1020 nm. Binned to 3-minute time bins we achieve an rms of 49 ppm for the combined broadband light curve. We construct a transmission spectrum with 20 spectrophotometric bins each spanning 20 nm and compare it to models of clear, 1$\times$ solar composition atmospheres. We rule out this atmospheric case with a surface pressure of 10 bars to $3.2 σ$ confidence, and with a surface pressure of 1 bar to $3.1 σ$ confidence. Upcoming secondary eclipse observations of LTT~1445Ab with JWST will further probe the cases of a high mean molecular weight atmosphere, a hazy or cloudy atmosphere, or no atmosphere at all on this terrestrial world.

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arXiv2022

Is ozone a reliable proxy for molecular oxygen? I. The O2-O3 relationship for Earth-like atmospheres

Molecular oxygen (O2) paired with a reducing gas is regarded as a promising biosignature pair for the atmospheric characterization of terrestrial exoplanets. In circumstances when O2 may not be detectable in a planetary atmosphere (e.g., at mid-IR wavelengths) it has been suggested that ozone (O3), the photochemical product of O2, could be used as a proxy to infer the presence of O2. However, O3 production has a nonlinear dependence on O2 and is strongly influenced by the UV spectrum of the host star. To evaluate the reliability of O3 as a proxy for O2, we used Atmos, a 1D coupled climate/photochemistry code, to study the O2-O3 relationship for "Earth-like" habitable zone planets around a variety of stellar hosts (G0V-M5V) and O2 abundances. Overall, we found that the O2-O3 relationship differed significantly with stellar hosts and resulted in different trends for hotter stars (G0V-K2V) vs cooler stars (K5V-M5V). Planets orbiting hotter host stars counter-intuitively experience an increase in O3 when O2 levels are initially decreased from 100% Earth's present atmospheric level (PAL), with a maximum O3 abundance occurring at 25-55% PAL O2. As O2 abundance initially decreases, larger amounts of UV photons capable of O2 photolysis reach the lower (denser) regions of the atmosphere where O3 production is more efficient, resulting in these increased O3 levels. This effect does not occur for cooler host stars (K5V-M5V), as the weaker incident UV flux does not allow O3 formation to occur at dense enough regions of the atmosphere where the faster O3 production can outweigh a smaller source of O2 from which to create O3. Overall it will be extremely difficult (or impossible) to infer precise O2 levels from an O3 measurement, however, with information about the UV spectrum of the host star and context clues, O3 will provide valuable information about potential surface habitability of an exoplanet.

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arXiv2022

Mass Transport in a Moist Planetary Climate Model

Planetary Climate Models (PCMs) are developed to explore planetary climates other than the Earth. Therefore, the methods implemented need to be suitable for a large diversity of conditions. Every planet with a significant atmosphere has condensible cycles (e.g., hydrological cycle), which can play an essential role in the planet's appearance and environment. We must accurately represent a condensible cycle in our planet simulations to build a powerful planetary climate predictor. OASIS is a 3D PCM capable of self-consistently representing the main physical processes that drive a planet's environment. In this work, we improve the representation of mass transport in OASIS, which is the first step towards a complete and flexible implementation of a condensible cycle. We implement an upwind-biased scheme on a piece-wise linear approximation with a flux-limiter to solve the mass transport equation. We first benchmark the new scheme on a 2D problem that confirms the superior properties of the new method over the central finite-volume method in terms of performance, accuracy and shape-preserving mass distribution. Due to the new scheme's less dispersive nature, we do not have to apply any unphysical diffusion to maintain the model stable. OASIS includes the new improved solver in the total mass and the tracers (e.g., clouds/hazes and individual gas chemical species) transport. We couple the new formulation with physical schemes and validate the new code on two 3D simulations of an ocean Earth-like planet and an ocean tidally-locked planet. The new OASIS simulations are robust and do not show any known problems from the dynamics-physics coupling. We show that the two simulations capture the main characteristics of ocean planet atmospheres and are easy to set up. We propose these two simulations to be the first standard benchmark tests for models built to explore moist planetary environments.

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arXiv2022

Exoplanet atmospheres at high resolution through a modest-size telescope. Fe II in MASCARA-2b and KELT-9b with FIES on the Nordic Optical Telescope

Ground-based, high-resolution spectrographs are providing us with an unprecedented view of the dynamics and chemistry of the atmospheres of planets outside the Solar System. While there is a large number of stable and precise high-resolution spectrographs on modest-size telescopes, it is the spectrographs at observatories with apertures larger than 3.5 metres that dominate the atmospheric follow-up of exoplanets. In this work, we explore the potential of characterising exoplanetary atmospheres with FIES, a high-resolution spectrograph at the 2.56 metre Nordic Optical Telescope. We observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit of KELT-9 b to search for atomic iron, a species that has been recently discovered in both neutral and ionised forms in the atmospheres of these ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we detect a signal of Fe II at the $4.5σ$ and $4.0σ$ level in the transits of MASCARA-2 b. We also detect Fe II in the transit of KELT-9 b at the $8.5σ$ level. Although we do not find any significant Doppler shift in the signal of MASCARA-2 b, we do measure a moderate blueshift (3-6 km/s) of the feature in KELT-9 b, which might be a manifestation of high-velocity winds transporting Fe II from the planetary dayside to the nightside. Our work demonstrates the feasibility of investigating exoplanet atmospheres with FIES, potentially unlocking a wealth of additional atmosphere detections with this and other high-resolution spectrographs mounted on similar-size telescopes.

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arXiv2022

The THOR+HELIOS general circulation model: multi-wavelength radiative transfer with accurate scattering by clouds/hazes

General circulation models (GCMs) provide context for interpreting multi-wavelength, multi-phase data of the atmospheres of tidally locked exoplanets. In the current study, the non-hydrostatic THOR GCM is coupled with the HELIOS radiative transfer solver for the first time, supported by an equilibrium chemistry solver (FastChem), opacity calculator (HELIOS-K) and Mie scattering code (LX-MIE). To accurately treat the scattering of radiation by medium-sized to large aerosols/condensates, improved two-stream radiative transfer is implemented within a GCM for the first time. Multiple scattering is implemented using a Thomas algorithm formulation of the two-stream flux solutions, which decreases the computational time by about 2 orders of magnitude compared to the iterative method used in past versions of HELIOS. As a case study, we present four GCMs of the hot Jupiter WASP-43b, where we compare the temperature, velocity, entropy, and streamfunction, as well as the synthetic spectra and phase curves, of runs using regular versus improved two-stream radiative transfer and isothermal versus non-isothermal layers. While the global climate is qualitatively robust, the synthetic spectra and phase curves are sensitive to these details. A THOR+HELIOS WASP-43b GCM (horizontal resolution of about 4 degrees on the sphere and with 40 radial points) with multi-wavelength radiative transfer (30 k-table bins) running for 3000 Earth days (864,000 time steps) takes about 19-26 days to complete depending on the type of GPU.

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arXiv2021

Mining the Ultra-Hot Skies of HAT-P-70b: Detection of a Profusion of Neutral and Ionized Species

With an equilibrium temperature above 2500 K, the recently discovered HAT-P-70 b belongs to a new class of exoplanets known as ultra-hot Jupiters: extremely irradiated gas giants with day-side temperatures that resemble those found in stars. These ultra-hot Jupiters are among the most amenable targets for follow-up atmospheric characterization through transmission spectroscopy. Here, we present the first analysis of the transmission spectrum of HAT-P-70 b using high-resolution data from the HARPS-N spectrograph of a single transit event. We use a cross-correlation analysis and transmission spectroscopy to look for atomic and molecular species in the planetary atmosphere. We detect absorption by Ca II, Cr I, Cr II, Fe I, Fe II, H I, Mg I, Na I and V I, and we find tentative evidence of Ca I and Ti II. Overall, these signals appear blue-shifted by a few km s$^{-1}$, suggestive of winds flowing at high velocity from the day-side to the night-side. We individually resolve the Ca II H & K lines, the Na I doublet, and the H$α$, H$β$ and H$γ$ Balmer lines. The cores of the Ca II and H I lines form well above the continuum, indicating the existence of an extended envelope. We refine the obliquity of this highly misaligned planet to $107.9^{+2.0}_{-1.7}$ degrees by examining the Doppler shadow that the planet casts on its A-type host star. These results place HAT-P-70 b as one of the exoplanets with the highest number of species detected in its atmosphere.

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arXiv2021

General Circulation Model Errors are Variable across Exoclimate Parameter Spaces

General circulation models are often used to explore exoclimate parameter spaces and classify atmospheric circulation regimes. Models are tuned to give reasonable climate states for standard test cases, such as the Held-Suarez test, and then used to simulate diverse exoclimates by varying input parameters such as rotation rates, instellation, atmospheric optical properties, frictional timescales and so on. In such studies, there is an implicit assumption that the model which works reasonably well for the standard test case will be credible at all points in an arbitrarily wide parameter space. Here, we test this assumption using the open-source general circulation model THOR to simulate atmospheric circulation on tidally locked Earth-like planets with rotation periods of 0.1 to 100 days. We find that the model error, as quantified by the ratio between physical and spurious numerical contributions to the angular momentum balance, is extremely variable across this range of rotation periods with some cases where numerical errors are the dominant component. Increasing model grid resolution does improve errors but using a higher-order numerical diffusion scheme can sometimes magnify errors for finite-volume dynamical solvers. We further show that to minimize error and make the angular momentum balance more physical within our model, the surface friction timescale must be smaller than the rotational timescale.

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arXiv2021

TOI-1518b: A Misaligned Ultra-hot Jupiter with Iron in its Atmosphere

We present the discovery of TOI-1518b -- an ultra-hot Jupiter orbiting a bright star $V = 8.95$. The transiting planet is confirmed using high-resolution optical transmission spectra from EXPRES. It is inflated, with $R_p = 1.875\pm0.053\,R_{\rm J}$, and exhibits several interesting properties, including a misaligned orbit (${240.34^{+0.93}_{-0.98}}$ degrees) and nearly grazing transit ($b =0.9036^{+0.0061}_{-0.0053}$). The planet orbits a fast-rotating F0 host star ($T_{\mathrm{eff}} \simeq 7300$ K) in 1.9 days and experiences intense irradiation. Notably, the TESS data show a clear secondary eclipse with a depth of $364\pm28$ ppm and a significant phase curve signal, from which we obtain a relative day-night planetary flux difference of roughly 320 ppm and a 5.2$σ$ detection of ellipsoidal distortion on the host star. Prompted by recent detections of atomic and ionized species in ultra-hot Jupiter atmospheres, we conduct an atmospheric cross-correlation analysis. We detect neutral iron (${5.2σ}$), at $K_p = 157^{+68}_{-44}$ km s$^{-1}$ and $V_{\rm sys} = -16^{+2}_{-4}$ km s$^{-1}$, adding another object to the small sample of highly irradiated gas-giant planets with Fe detections in transmission. Detections so far favor particularly inflated gas giants with radii $\gtrsim 1.78\,R_{\rm J}$; although this may be due to observational bias. With an equilibrium temperature of $T_{\rm eq}=2492\pm38$ K and a measured dayside brightness temperature of $3237\pm59$ K (assuming zero geometric albedo), TOI-1518b is a promising candidate for future emission spectroscopy to probe for a thermal inversion.

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arXiv2021

HST PanCET Program: A Complete Near-UV to Infrared Transmission Spectrum for the Hot Jupiter WASP-79b

We present a new optical transmission spectrum of the hot Jupiter WASP-79b. We observed three transits with the STIS instrument mounted on HST, spanning 0.3 - 1.0 um. Combining these transits with previous observations, we construct a complete 0.3 - 5.0 um transmission spectrum of WASP-79b. Both HST and ground-based observations show decreasing transit depths towards blue wavelengths, contrary to expectations from Rayleigh scattering or hazes. We infer atmospheric and stellar properties from the full near-UV to infrared transmission spectrum of WASP-79b using three independent retrieval codes, all of which yield consistent results. Our retrievals confirm previous detections of H$_{2}$O (at 4.0$σ$ confidence), while providing moderate evidence of H$^{-}$ bound-free opacity (3.3$σ$) and strong evidence of stellar contamination from unocculted faculae (4.7$σ$). The retrieved H$_{2}$O abundance ($\sim$ 1$\%$) suggests a super-stellar atmospheric metallicity, though stellar or sub-stellar abundances remain consistent with present observations (O/H = 0.3 - 34$\times$ stellar). All three retrieval codes obtain a precise H$^{-}$ abundance constraint: log(X$_{\rm{H^{-}}}$) $\approx$ -8.0 $\pm$ 0.7. The potential presence of H$^{-}$ suggests that JWST observations may be sensitive to ionic chemistry in the atmosphere of WASP-79b. The inferred faculae are $\sim$ 500 K hotter than the stellar photosphere, covering $\sim$ 15$\%$ of the stellar surface. Our analysis underscores the importance of observing UV - optical transmission spectra in order to disentangle the influence of unocculted stellar heterogeneities from planetary transmission spectra.

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arXiv2021

HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres

Computing and using opacities is a key part of modeling and interpreting data of exoplanetary atmospheres. Since the underlying spectroscopic line lists are constantly expanding and currently include up to ~ 10^10 - 10^11 transition lines, the opacity calculator codes need to become more powerful. Here we present major upgrades to the HELIOS-K GPU-accelerated opacity calculator and describe the necessary steps to process large line lists within a reasonable amount of time. Besides performance improvements, we include more capabilities and present a toolbox for handling different atomic and molecular data sets: from downloading and pre-processing the data to performing the opacity calculations in a user-friendly way. HELIOS-K supports line lists from ExoMol, HITRAN, HITEMP, NIST, Kurucz and VALD3. By matching the resolution of 0.1 cm^-1 and cutting length of 25 cm^-1 used by the ExoCross code for timing performance (251 seconds excluding data read-in time), HELIOS-K can process the ExoMol BT2 water line list in 12.5 seconds. Using a resolution of 0.01 cm^-1, it takes 45 seconds - equivalent to about 10^7 lines per second. As a wavenumber resolution of 0.01 cm^-1 suffices for most exoplanetary atmosphere spectroscopic calculations, we adopt this resolution in calculating opacity functions for several hundred atomic and molecular species, and make them freely available on the open-access DACE database. For the opacity calculations of the database, we use a cutting length of 100 cm^-1 for molecules and no cutting length for atoms. Our opacities are available for downloading from https://dace.unige.ch/opacityDatabase and may be visualized using https://dace.unige.ch/opacity.

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arXiv2020

Modelling the 3D Climate of Venus with OASIS

Flexible 3D models to explore the vast diversity of terrestrial planets and interpret observational data are still in their early stages. In this work, we present OASIS: a novel and flexible 3D virtual planet laboratory. With OASIS we envision a platform that couples self-consistently seven individual modules representing the main physical and chemical processes that shape planetary environments. Additionally, OASIS is capable of producing simulated spectra from different instruments and observational techniques. In this work we focus on the benchmark test of coupling four of the physical modules: fluid dynamics, radiation, turbulence and surface/soil. To test the OASIS platform, we produced 3D simulations of the Venus climate and its atmospheric circulation and study how the modeled atmosphere changes with various cloud covers, atmospheric heat capacity, and surface friction. 3D simulations of Venus are challenging because they require long integration times with a computationally expensive radiative transfer code. By comparing OASIS results with observational data, we verify that the new model is able to successfully simulate Venus. With simulated spectra produced directly from the 3D simulations, we explore the capabilities of future missions, like LUVOIR, to observe Venus analogs located at a distance of 10 pc. With OASIS, we have taken the first steps to build a sophisticated and very flexible platform capable of studying the environment of terrestrial planets, which will be an essential tool to characterize observed terrestrial planets and plan future observations.

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arXiv2020

THOR 2.0: Major Improvements to the Open-Source General Circulation Model

THOR is the first open-source general circulation model (GCM) developed from scratch to study the atmospheres and climates of exoplanets, free from Earth- or Solar System-centric tunings. It solves the general non-hydrostatic Euler equations (instead of the primitive equations) on a sphere using the icosahedral grid. In the current study, we report major upgrades to THOR, building upon the work of Mendonça et al. (2016). First, while the Horizontally Explicit Vertically Implicit (HEVI) integration scheme is the same as that described in Mendonça et al. (2016), we provide a clearer description of the scheme and improved its implementation in the code. The differences in implementation between the hydrostatic shallow (HSS), quasi-hydrostatic deep (QHD) and non-hydrostatic deep (NHD) treatments are fully detailed. Second, standard physics modules are added: two-stream, double-gray radiative transfer and dry convective adjustment. Third, THOR is tested on additional benchmarks: tidally-locked Earth, deep hot Jupiter, acoustic wave, and gravity wave. Fourth, we report that differences between the hydrostatic and non-hydrostatic simulations are negligible in the Earth case, but pronounced in the hot Jupiter case. Finally, the effects of the so-called "sponge layer", a form of drag implemented in most GCMs to provide numerical stability, are examined. Overall, these upgrades have improved the flexibility, user-friendliness, and stability of THOR.

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arXiv2019

Angular Momentum and Heat Transport on Tidally Locked Hot Jupiter Planets

The atmospheric circulation in the upper atmosphere of hot Jupiter planets is strongly influenced by the incoming stellar radiation. In this work we explore the results from a 3D atmospheric model and revisit the main processes driving the circulation in hot Jupiter planets. We use the angular momentum transport as a diagnostic and carry out a Fourier analysis to identify the atmospheric waves involved. We find that the coupling between the angular momentum transported horizontally by the semi-diurnal tide and the mean circulation is the mechanism responsible for producing the strong jet at low latitudes. Our simulations indicate the possible formation of atmospheric indirect cells at low latitudes. The formation of these cells is induced by the presence of the semi-diurnal tide that is driven by the stellar irradiation. The tropical circulation has an important impact transporting heat and momentum from the upper towards the lower atmosphere. One of the consequences of this heat and momentum transport is a global increase of the temperature. We show that the initial conditions do not affect the output of the reference simulation. However, when the period of rotation of the planet was increased ($P_{rot} > 5$ Earth days), vertical transport by stationary waves became stronger, transient waves became non-negligible, and Coriolis influence less dominant, which allowed a steady state with a strong retrograde jet to be stable. We found that at least two statically steady state solutions exist for the same planet parameters.

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arXiv2019

Self-luminous and irradiated exoplanetary atmospheres explored with HELIOS

We present new methodological features and physical ingredients included in the 1D radiative transfer code HELIOS, improving the hemispheric two-stream formalism. We conduct a thorough intercomparison survey with several established forward models, including COOLTLUSTY, PHOENIX, and find satisfactory consistency with their results. Then, we explore the impact of (i) different groups of opacity sources, (ii) a stellar path length adjustment, and (iii) a scattering correction on self-consistently calculated atmospheric temperatures and planetary emission spectra. First, we observe that temperature-pressure (T-P) profiles are very sensitive to the opacities included, with metal oxides, hydrides, the alkali atoms (and ionized hydrogen) playing an important role for the absorption of shortwave radiation (in very hot surroundings). Moreover, if these species are sufficiently abundant, they are likely to induce non-monotonic T-P profiles. Second, without the stellar path length adjustment, the incoming stellar flux is significantly underestimated for zenith angles above 80°, which somewhat affects the upper atmospheric temperatures and the planetary emission. Third, the scattering correction improves the accuracy of the computation of the reflected stellar light by ~10%. We use HELIOS to calculate a grid of cloud-free atmospheres in radiative-convective equilibrium for self-luminous planets for a range of effective temperatures, surface gravities, metallicities, and C/O ratios, to be used by planetary evolution studies. Furthermore, we calculate dayside temperatures and secondary eclipse spectra for a sample of exoplanets for varying chemistry and heat redistribution. These results may be used to make predictions on the feasibility of atmospheric characterizations with future observations.

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arXiv2018

Three-Dimensional Circulation Driving Chemical Disequilibrium in WASP-43b

Spectral features in the observed spectra of exoplanets depend on the composition of their atmospheres. A good knowledge of the main atmospheric processes that drive the chemical distribution is therefore essential to interpret exoplanetary spectra. An atmosphere reaches chemical equilibrium if the rates of the forward and backward chemical reactions converge to the same value. However, there are atmospheric processes, such as atmospheric transport, that destabilize this equilibrium. In this work we study the changes in composition driven by a 3D wind field in WASP-43b using our Global Circulation Model, THOR. Our model uses validated temperature- and pressure-dependent chemical timescales that allow us to explore the disequilibrium chemistry of CO, CO$_2$, H$_2$O and CH$_4$. In WASP-43b the formation of the equatorial jet has an important impact in the chemical distribution of the different species across the atmosphere. At low latitudes the chemistry is longitudinally quenched, except for CO$_2$ at solar abundances. The polar vortexes have a distinct chemical distribution since these are regions with lower temperature and atmospheric mixing. Vertical and latitudinal mixing have a secondary impact in the chemical transport. We determine graphically the effect of disequilibrium on observed emission spectra. Our results do not show any significant differences in the emission spectra between the equilibrium and disequilibrium solutions for C/O = 0.5. However, if C/O is increased to 2.0, differences in the spectra due to the disequilibrium chemistry of CH$_4$ become non-negligible. In some spectral ranges the emission spectra can have more than 15$\%$ departures from the equilibrium solution.

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