HD 209458b Research Articles

The ANTARESS workflow

High-resolution spectrographs open a detailed window onto the atmospheres of stars and planets. As the number of systems observed with different instruments grows, it is crucial to develop a standard in analyzing spectral time series of exoplanet transits and occultations, for the benefit of reproducibility. Here, we introduce the ANTARESS workflow, a set of methods aimed at processing high-resolution spectroscopy datasets in a robust way and extracting accurate exoplanetary and stellar spectra. While a fast preliminary analysis can be run on order-merged 1D spectra and cross-correlation functions (CCFs), the workflow was optimally designed for extracted 2D echelle spectra to remain close to the original detector counts, limit the spectral resampling, and propagate the correlated noise. Input data from multiple instruments and epochs were corrected for relevant environmental and instrumental effects, processed homogeneously, and analyzed independently or jointly. In this first paper, we show how planet-occulted stellar spectra extracted along the transit chord and cleaned from planetary contamination provide a direct comparison with theoretical stellar models and enable a spectral and spatial mapping of the photosphere. We illustrate this application of the workflow to archival ESPRESSO data, using the Rossiter-McLaughlin effect Revolutions (RMR) technique to confirm the spin-orbit alignment of HD 209458b and unveil biases in WASP-76b’s published orbital architecture. Because the workflow is modular and its concepts are general, it can support new methods and be extended to additional spectrographs to find a range of applications beyond the proposed scope. In a companion paper, we will present how planet-occulted spectra can be processed further to extract and analyze planetary spectra decontaminated from the star, providing clean and direct measurements of atmospheric properties.

Probing Na in giant exoplanets with ESPRESSO and 3D NLTE stellar spectra

Neutral sodium was the first atom that was detected in an exoplanetary atmosphere using the transmission spectroscopy technique. To date, it remains the most successfully detected species due to its strong doublet in the optical at 5890\ A and 5896\ A . However, the center-to-limb variation (CLV) of these lines in the host star can bias the Na I detection. When combined with the Rossiter-McLaughlin (RM) effect, the CLV can mimic or obscure a planetary absorption feature if it is not properly accounted for. This work aims to investigate the impact of three-dimensional (3D) radiation hydrodynamic stellar atmospheres and non-local thermodynamic equilibrium (NLTE) radiative transfer on the modeling of the CLV+RM effect in single-line transmission spectroscopy to improve the detection and characterization of exoplanet atmospheres. We produced a grid of 3D NLTE synthetic spectra for Na I for FGK-type dwarfs within the following parameter space: $T_ eff =4500-6500$\,K, $ g =4.0-5.0$, and Fe/H . This grid was then interpolated to match the stellar parameters of four stars hosting well-known giant exoplanets, generating stellar spectra to correct for the CLV+RM effect in their transmission spectra. We used archival observations taken with the high-resolution ESPRESSO spectrograph. Our work confirms the Na I detections in three systems, namely WASP-52b, WASP-76b, and WASP-127b, also improving the accuracy of the measured absorption depth. Furthermore, we find that 3D NLTE stellar models can explain the spectral features in the transmission spectra of HD 209458b without the need for any planetary absorption. In the grid of stellar synthetic spectra, we observe that the CLV effect is stronger for stars with low $T_ eff $ and high $ g$. However, the combined effect of CLV and RM is highly dependent on the orbital geometry of the planet-star system. With the continuous improvement of instrumentation, it is crucial to use the most accurate stellar models available to correct for the CLV+RM effect in high-resolution transmission spectra to achieve the best possible characterization of exoplanet atmospheres. This will be fundamental in preparation for instruments such as ANDES at the Extremely Large Telescope to fully exploit its capabilities in the near future. We make our grid of 3D NLTE synthetic spectra for Na I publicly available.

High-resolution transmission spectroscopy of the hot-Saturn HD 149026b

Advances in modern technology have enabled the characterization of exoplanetary atmospheres, which can be achieved by exploitation of the transmission spectroscopy technique. We performed visible (VIS) and near-infrared (NIR) high-resolution spectroscopic observations of one transit of HD 149026b, a close-in orbit sub-Saturn exoplanet by using the GIARPS configuration at the Telescopio Nazionale Galileo (TNG). We first analyzed the radial-velocity data, refining the value of the projected spin-orbit obliquity (lambda ). We then performed transmission spectroscopy, looking for absorption signals from the planetary atmosphere. We find no evidence for Halpha \, D2$-$D1 or in the VIS and metastable helium triplet in the NIR using a line-by-line approach. The non-detection of HeI is also supported by theoretical simulations. With the use of the cross-correlation technique (CCF), we do not detect or VO in the visible, or indeed CH$_4$, CO$_2$, H$_2$O, HCN, NH$_3$, or VO in the NIR. Our non-detection of in the planetary atmosphere is in contrast with a previous detection. We performed injection-retrieval tests, finding that our dataset is sensitive to our \, model. The non-detection supports the \, cold-trap theory, which is valid for planets with eq <$ 2200 K, such as HD 149026b. Although we do not attribute it directly to the planet, we find a possibly significant \, signal that is highly redshifted (simeq +20 with respect to the planetary rest frame. Redshifted signals are also found in the \, and \, maps. While we can exclude an eccentric orbit as the cause of this redshifted \, signal, we investigated the possibility of material accretion falling onto the star --- which is possibly supported by the presence of strong \, in the stellar spectrum --- but obtained inconclusive results. The analysis of multiple transits datasets could shed more light on this target.

Transition from super-alfvenic to sub-alfvenic stellar wind flow passing by an exoplanet, using the example of HD 209458b

Transition from super-alfvenic to sub-alfvenic stellar wind flow passing by an exoplanet, using the example of HD 209458b

Identifying and fitting eclipse maps of exoplanets with cross-validation

ABSTRACT Eclipse mapping uses the shape of the eclipse of an exoplanet to measure its two-dimensional structure. Light curves are mostly composed of longitudinal information, with the latitudinal information only contained in the brief ingress and egress of the eclipse. This imbalance can lead to a spuriously confident map, where the longitudinal structure is constrained by out-of-eclipse data and the latitudinal structure is wrongly determined by the priors on the map. We present a new method to address this issue. The method tests for the presence of an eclipse mapping signal using k-fold cross-validation to compare the performance of a simple mapping model to the null hypothesis of a uniform disc. If a signal is found, the method fits a map with more degrees of freedom, optimizing its information content. The information content is varied by penalizing the model likelihood by a factor proportional to the spatial entropy of the map, optimized by cross-validation. We demonstrate this method for simulated data sets then apply it to three observational data sets. The method identifies an eclipse mapping signal for JWST MIRI/LRS observations of WASP-43b but does not identify a signal for JWST NIRISS/SOSS observations of WASP-18b or Spitzer Space Telescope observations of HD 189733b. It is possible to fit eclipse maps to these data sets, but we suggest that these maps are overfitting the eclipse shape. We fit a new map with more spatial freedom to the WASP-43b data set and show a flatter east–west structure than previously derived.

Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet.

As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization1-3. It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition4, chemistry5,6, aerosols7 to atmospheric dynamics8, escape9 and modelling techniques10,11. Previous studies of HD 189733b have detected carbon and oxygen-bearing molecules H2O and CO (refs. 12,13) in the atmosphere. The presence of CO2 and CH4 has been claimed14,15 but later disputed12,16,17. The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations18, varies from depletion19,20 to enhancement21,22, hindered by limited wavelength coverage and precision of the observations. Here we report detections of H2O (13.4σ), CO2 (11.2σ), CO (5σ) and H2S (4.5σ) in the transmission spectrum (2.4-5.0 μm) of HD 189733b. With an equilibrium temperature of about 1,200 K, H2O, CO and H2S are the main reservoirs for oxygen, carbon and sulfur. Based on the measured abundances of these three main volatile elements, we infer an atmospheric metallicity of three to five times stellar. The upper limit on the methane abundance at 5σ is 0.1 ppm, which indicates a low carbon-to-oxygen ratio (<0.2), suggesting formation through the accretion of water-rich icy planetesimals. The low oxygen-to-sulfur and carbon-to-sulfur ratios also support the planetesimal accretion formation pathway23.

The Atmosphere of HD 149026b: Low Metal Enrichment and Weak Energy Transport

Recent JWST eclipse spectra of the high-density hot Saturn HD 149026b between 2.35 and 5.08 μm have allowed for in-depth study of its atmosphere. To understand its atmospheric properties, we have created a grid of 1D radiative-convective–thermochemical–equilibrium atmosphere models and spectra with PICASO 3.0. In agreement with previous work, we find that the presence of gaseous TiO creates a thermal inversion, which is inconsistent with the data. The presence of gaseous VO, however, which condenses at temperatures 200 K cooler, does not cause such inversions but alters the temperature–pressure profile of the atmosphere. We estimate an atmospheric metallicity of 14−8+12× solar without VO and 20−8+11× solar with VO, a factor of ∼10 times smaller than previous work from Bean et al., who relied on atmosphere retrievals. We attribute this significant difference in metallicity to a larger temperature gradient at low pressures in radiative equilibrium models. Such models with lower metallicities readily fit the strong CO2 feature at 4.3 μm. Our lower estimated metallicity makes HD 149026b more consistent with the mass–metallicity relationship for other giant planets. We find a C/O ratio of 0.67−0.27+0.06 with and without VO. The best-fit heat redistribution factor without VO is 1.17, a very high value suggesting very little dayside energy transport and no energy transport to the nightside. The heat redistribution factor shrinks to a more plausible value of 0.91−0.05+0.05 , with VO, which we regard as circumstantial evidence for the molecule in the atmosphere of HD 149026b.

Correction to: 3D simulations of photochemical hazes in the atmosphere of hot Jupiter HD 189733b

Correction to: 3D simulations of photochemical hazes in the atmosphere of hot Jupiter HD 189733b

FRECKLL: Full and Reduced Exoplanet Chemical Kinetics DistiLLed

We introduce a new Python 1D chemical kinetic code, Full and Reduced Exoplanet Chemical Kinetics distiLLed (FRECKLL), to evolve large chemical networks efficiently. FRECKLL employs “distillation” in computing the reaction rates, which minimizes the error bounds to the minimum allowed by double precision values (ϵ ≤ 10−15). Compared to summation of rates with traditional algorithms like pairwise summation, distillation provides a tenfold reduction in solver time for both full and reduced networks. Both the full and reduced Venot2020 networks are packaged in FRECKLL as well as a TauREx 3.1 plug-in for usage in forward modeling and retrievals of exoplanet atmospheres. We present TauREx retrievals performed on a simulated HD 189733b JWST spectra using the full and reduced Venot2020 chemical networks and demonstrate the viability of total disequilibrium chemistry retrievals and the ability for JWST to detect disequilibrium processes.

Methods for Incorporating Model Uncertainty into Exoplanet Atmospheric Analysis

A key goal of exoplanet spectroscopy is to measure atmospheric properties, such as abundances of chemical species, in order to connect them to our understanding of atmospheric physics and planet formation. In this new era of high-quality JWST data, it is paramount that these measurement methods are robust. When comparing atmospheric models to observations, multiple candidate models may produce reasonable fits to the data. Typically, conclusions are reached by selecting the best-performing model according to some metric. This ignores model uncertainty in favor of specific model assumptions, potentially leading to measured atmospheric properties that are overconfident and/or incorrect. In this paper, we compare three ensemble methods for addressing model uncertainty by combining posterior distributions from multiple analyses: Bayesian model averaging, a variant of Bayesian model averaging using leave-one-out predictive densities, and stacking of predictive distributions. We demonstrate these methods by fitting the Hubble Space Telescope (HST) + Spitzer transmission spectrum of the hot Jupiter HD 209458b using models with different cloud and haze prescriptions. All of our ensemble methods lead to uncertainties on retrieved parameters that are larger but more realistic and consistent with physical and chemical expectations. Since they have not typically accounted for model uncertainty, uncertainties of retrieved parameters from HST spectra have likely been underreported. We recommend stacking as the most robust model combination method. Our methods can be used to combine results from independent retrieval codes and from different models within one code. They are also widely applicable to other exoplanet analysis processes, such as combining results from different data reductions.

The PEPSI Exoplanet Transit Survey (PETS) – V. New Na d transmission spectra indicate a quieter atmosphere on HD 189733b

ABSTRACT Absorption lines from exoplanet atmospheres observed in transmission allow us to study atmospheric characteristics such as winds. We present a new high-resolution transit time-series of HD 189733b, acquired with the PEPSI instrument at the LBT and analyse the transmission spectrum around the Na d lines. We model the spectral signature of the RM-CLV-effect using synthetic PHOENIX spectra based on spherical LTE atmospheric models. We find an Na d absorption signature between the second and third contact but not during the ingress and egress phases, which casts doubt on the planetary origin of the signal. Presupposing a planetary origin of the signal, the results suggest a weak day-to-nightside streaming wind in the order of 0.7 km s−1 and a moderate super-rotational streaming wind in the order of 3–4 km s−1, challenging claims of prevailing strong winds on HD 189733b.

Transition from Super-Alfvénic to Sub-Alfvénic Stellar Wind Flow Passing by an Exoplanet, Using the Example of HD 209458b

Depending on the distance of the exoplanet from the central star and the properties of this star, different regimes of stellar wind flow around it arise. If the exoplanet is located at a distance up to the Alfvén radius, where the wind speed is equal to the Alfvén speed, or the Alfvén Mach number \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{M}_{{\ ext{A}}}} = 1$$\\end{document}, the exoplanet generates Alfvén wings. If it is situated beyond the Alfvén radius, a comet-like magnetosphere appears, similar to that of the planets of the Solar System. The paper examines how the transition from one flow regime to another can be described on the base of a paraboloid model of the magnetospheric magnetic field using the example of exoplanet HD 209458b.

Color measurements of the polarized light scattered by the dust in protoplanetary disks

Context. Many reflected light images of protoplanetary disks have been obtained with ground-based high-contrast instruments. Quantitative measurements of the reflected radiation provide strong constraints on the scattering dust which can clarify the dust particle evolution in these disks and the composition of the forming planets. Aims. We derived the wavelength dependence of the polarized reflectivity (Qˆφ/I*)λ or color for a sample of disks to contrain the dust based on these data. Further we searched for systematic differences in the dust properties between subgroups of disks. Methods. We selected from the ESO archive polarized imaging for 11 protoplanetary disks obtained at visible and near-infrared wavelengths with the SPHERE/ZIMPOL and SPHERE/IRDIS high contrast instruments. All disks have bright and well-resolved structures, such as rings or spirals, which allow accurate determinations of the intrinsic polarized reflectivity Qˆφ/I* at multiple wavelengths. For this, we corrected the observations for the smearing effects caused by the point spread functions (PSFs) of the individual dataset with a novel correction procedure applicable to inclined disks. For the 11 disks, we derived a total of 31 Qˆφ/I* values for wavelengths from 0.62 μm (R band) to 2.2 μm (Ks band) and compared our results, if possible, with previous determinations. For each disk, we derived a polarized reflectivity color ηV/IR between a visible band λ &lt; 1 μm and a near-IR band λ &gt; 1 μm and other wavelength combinations. We also consider model calculations for the polarized reflectivity colors η for protoplanetary disks to constrain the scattering properties of the dust. Results. The polarized reflectivities for the investigated disks structures are at a typical level between Qφ/I★ ~ 0.1% to 1.0%. These values depend strongly on the observing conditions and a correction for the PSF smearing effects is essential to obtain the intrinsic values Qˆφ/I*. Corrected values Qˆφ/I* are on average about a factor of 1.6 higher than the observed values. We checked the accuracy of the PSF calibrations procedure with simulations and literature data, and show that the large systematic errors in the observational values are reduced to a relative level ΔQˆφ/Qˆφ ≈ 10% or even less. The high accuracy yields wavelength gradients for the polarized reflectivity (Qˆφ/I*)φ or colors η which are significantly different between different objects. We find in our sample for all disks around Herbig stars (HD 169142, HD 135344B, HD 100453, MWC 758, and HD 142527) a red color ηv/IR &gt; 0.5, while four out of six disks around T Tauri stars (PDS 70, TW Hya, RX J1615, and PDS 66) are gray −0.5 &lt; ηV/IR &lt; 0.5. The red colors support the presence of rather compact dust grains, while the absence of blue colors (except for the near-infrared color of PDS 66) is not compatible with very porous aggregates composed of small monomers. We suspect, that the very red colors ηV/IR ≈ 2 obtained for LkCa 15 and MWC 758 could be the result of an "extra" reddening of the radiation illuminating the disk caused by absorbing hot dust near the star. We discuss the prospects of further improvements for the derivation of dust properties in these disks if the fractional polarization 〈pψ〉 or other parameters of the reflected light are also taken into account in future studies.

JWST Transmission Spectroscopy of HD 209458b: A Supersolar Metallicity, a Very Low C/O, and No Evidence of CH4, HCN, or C2H2

We present the transmission spectrum of the original transiting hot Jupiter HD 209458b from 2.3 to 5.1 μm as observed with the NIRCam instrument on the James Webb Space Telescope (JWST). Previous studies of HD 209458b’s atmosphere have given conflicting results on the abundance of H2O and the presence of carbon- and nitrogen-bearing species, which have significant ramifications on the inferences of the planet’s metallicity (M/H) and carbon-to-oxygen (C/O) ratio. We detect strong features of H2O and CO2 in the JWST transmission spectrum, which when interpreted using a retrieval that assumes thermochemical equilibrium and fractional gray cloud opacity yields 3−1+4 × solar metallicity and C/O = 0.11−0.06+0.12 . The derived metallicity is consistent with the atmospheric metallicity–planet mass trend observed in solar gas giants. The low C/O ratio suggests that this planet has undergone significant contamination by evaporating planetesimals while migrating inward. We are also able to place upper limits on the abundances of CH4, C2H2, and HCN of log( χCH4 ) = −5.6, log( χC2H2 ) = −5.7, and log( χHCN ) = −5.1, which are in tension with the recent claim of a detection of these species using ground-based cross-correlation spectroscopy. We find that HD 209458b has a weaker CO2 feature size than WASP-39b when comparing their scale-height-normalized transmission spectra. On the other hand, the size of HD 209458b’s H2O feature is stronger, thus reinforcing the low C/O inference.

A re-analysis of equilibrium chemistry in five hot Jupiters

Aims. Studies of chemistry and chemical composition are fundamental to exploring the formation histories of planets and planetary systems. We propose having another look at five targets to better determine their composition and the chemical mechanisms taking place in their atmospheres. We present a re-analysis of five hot Jupiters, combining multiple instruments and using Bayesian retrieval methods. We compare different combinations of molecules present in the simulated atmosphere and various chemistry types, as well as a range of cloud parametrizations. Following up on recent studies questioning the detection of Na and K in the atmosphere of HD 209458b as being potentially contaminated by stellar lines (when present), we study the impact on other retrieval parameters that may lead to misinterpretations of the presence of these alkali species. Methods. We used spatially scanned observations from the grisms G102 and G141 of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope, with a wavelength coverage of ~0.8 to ~1.7 microns. We analyzed these data with the publicly available Iraclis pipeline. We added data from Space Telescope Imaging Spectrograph (STIS) observations to increase our wavelength coverage from ~0.4 to ~1.7 µm. We then performed a Bayesian retrieval analysis with the open-source TauREx using a nested sampling algorithm. We carried out the retrieval, taking into account molecular abundances that vary freely and then with equilibrium chemistry. We explored the influence of including Na and K on the retrieval of the molecules from the atmosphere. Results. Our data re-analysis and Bayesian retrieval are consistent with previous studies, but we do find small differences in the retrieved parameters. After all, Na and K have no significant impact on the properties of the planet atmospheres. Therefore, we present here our new best-fit models, taking into account molecular abundances that are allowed to vary freely as well as the equilibrium chemistry. This work is a preparation for a future addition of a more sophisticated representation of the chemistry involved, while taking into account disequilibrium effects such as vertical mixing and photochemistry.

Another look at the dayside spectra of WASP-43b and HD 209458b: Are there scattering clouds?

ABSTRACT The search for clouds on the dayside of hot Jupiters has been disadvantaged due to the limited number of high quality space-based observations of their dayside. To date, retrieval studies have found no evidence for grey clouds on the dayside, however none of these studies explored the impact of scattering clouds. In this study we reanalyse the dayside emission spectrum of the hot Jupiter WASP-43b considering the different Spitzer data in the literature. We find that, in 2 of the 4 data sets explored, retrieving with a model that contains a scattering cloud is favoured over a cloud free model by a confidence of 3.13 - 3.36 σ. The other 2 data sets finds no evidence for scattering clouds. We find that the retrieved H2O abundance is consistent regardless of the Spitzer data used and is consistent with literature values. We perform the same analysis for the hot Jupiter HD 209458b and find no evidence for dayside clouds, consistent with previous studies.

The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b* *Revised Manuscript on 2022 June 7

The absorption signals of metastable He in HD 209458b and several other exoplanets can be explained via an escaping atmosphere model with a subsolar He/H ratio. The low abundance of helium can be a result of planet formation if there is a small amount of helium in their primordial atmosphere. However, another possibility is that the low He/H ratio is caused by the process of mass fractionation of helium in the atmosphere. In order to investigate the effect of fractionation in the hydrogen-helium atmosphere, we developed a self-consistent multi-fluid 1D hydrodynamic model based on the well-known open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be produced spontaneously in the multi-fluid model. We further modeled the transmission spectra of He 10830 lines for HD 209458b in a broad parameter space. The transmission spectrum of the observation can be fitted in the condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen, F He/F H, is 0.039. Our results indicate that the mass fractionation of helium to hydrogen can naturally interpret the low He/H ratio required by the observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the abundance of helium in the atmosphere is not needed even if its He abundance is similar to that of the Sun. The simulation presented in this work hints that in the escaping atmosphere, mass fractionation can also occur on other exoplanets, which needs to be explored further.

Confirmation of Subsolar Metallicity for WASP-77Ab from JWST Thermal Emission Spectroscopy

We present the dayside thermal emission spectrum of WASP-77Ab from 2.8 to 5.2 μm as observed with the NIRSpec instrument on the James Webb Space Telescope (JWST). WASP-77Ab was previously found to have a subsolar metallicity and a solar carbon-to-oxygen (C/O) ratio from H2O and CO absorption lines detected using high-resolution spectroscopy. By performing atmospheric retrievals on the JWST spectrum assuming chemical equilibrium, we find a subsolar metallicity [M/H] = and C/O ratio . We identify H2O and CO and constrain their abundances, and we find no CO2 in the spectrum. The JWST and high-resolution spectroscopy results agree within ∼1σ for the metallicity and within 1.8σ for the C/O ratio. However, our results fit less well in the picture painted by the shorter wavelength spectrum measured by Hubble Space Telescope Wide Field Camera 3. Comparing the JWST thermal emission spectra of WASP-77Ab and HD 149026b shows that both hot Jupiters have nearly identical brightness temperatures in the near-infrared but distinctly different atmospheric compositions. Our results reaffirm high-resolution spectroscopy as a powerful and reliable method to measure molecular abundances. Our results also highlight the incredible diversity of hot Jupiter atmospheric compositions.

Constraining the atmospheric elements in hot Jupiters with Ariel

ABSTRACT One of the main objectives of the European Space Agency’s Ariel telescope (launch 2029) is to understand the formation and evolution processes of a large sample of planets in our Galaxy. Important indicators of such processes in giant planets are the elemental compositions of their atmospheres. Here we investigate the capability of Ariel to constrain four key atmospheric markers: metallicity, C/O, S/O, and N/O, for three well-known, representative hot-Jupiter atmospheres observed with transit spectroscopy, i.e. HD 209458b, HD 189733b, and WASP-121b. We have performed retrieval simulations for these targets to verify how the planetary formation markers listed above would be recovered by Ariel when observed as part of the Ariel Tier 3 survey. We have considered eight simplified different atmospheric scenarios with a cloud-free isothermal atmosphere. Additionally, extra cases were tested to illustrate the effect of C/O and metallicity in recovering the N/O. From our retrieval results, we conclude that Ariel is able to recover the majority of planetary formation markers. The contributions from CO and CO2 are dominant for the C/O in the solar scenario. In a C-rich case, C2H2, HCN, and CH4 may provide additional spectral signatures that can be captured by Ariel. In our simulations, H2S is the main tracer for the S/O in hot-Jupiter atmospheres. In the super-solar metallicity cases and the cases with C/O &amp;gt; 1, the increased abundance of HCN is easily detectable and the main contributor to N/O, while other N-bearing species contribute little to the N/O in the investigated atmospheres.

Revised Properties and Dynamical History for the HD 17156 System

From the thousands of known exoplanets, those that transit bright host stars provide the greatest accessibility toward detailed system characterization. The first known such planets were generally discovered using the radial-velocity technique, then later found to transit. HD 17156b is particularly notable among these initial discoveries because it diverged from the typical hot-Jupiter population, occupying a 21.2 day eccentric (e = 0.68) orbit, offering preliminary insights into the evolution of planets in extreme orbits. Here we present new data for this system, including ground- and space-based photometry, radial velocities, and speckle imaging, that further constrain the system properties and stellar/planetary multiplicity. These data include photometry from the Transiting Exoplanet Survey Satellite that cover five transits of the known planet. We show that the system does not harbor any additional giant planets interior to 10 au. The lack of stellar companions and the age of the system indicate that the eccentricity of the known planet may have resulted from a previous planet–planet scattering event. We provide the results from dynamical simulations that suggest possible properties of an additional planet that culminated in ejection from the system, leaving a legacy of the observed high eccentricity for HD 17156b.