arXiv subjects

Ana Glidden

Publications and source records attributed to Ana Glidden.

At least 19 recordsLinked to original sources

arXiv2026

Leveraging Impact Parameter to Mitigate the Transit Light Source Effect: Early Insights from TRAPPIST-1

Stellar activity complicates exoplanet transmission spectra, particularly for smaller planets around M dwarfs with JWST. The transit light source (TLS) effect, the imprinting of spectral differences between the average stellar disk and the occulted transit chord onto the transmission spectrum, makes it challenging to directly use the out-of-transit spectrum to correct for stellar contamination. Theory and observations suggest that spots may concentrate towards higher latitudes when the Coriolis force is substantial relative to buoyancy, leaving the equatorial region relatively quiet. Here, we evaluate how the latitudinal distribution of active regions shapes the strength of the TLS effect for planets spanning a range of impact parameters ($b$), using TRAPPIST-1 as a testbed. We first construct a fiducial model to illustrate two distribution regimes. With our model, the moderate-$b$ outer TRAPPIST-1 planets (f, g, h) occult a more typical region of the stellar disk than the inner planets and are thereby less affected by the TLS effect, though their bias may vary more from visit-to-visit as these active regions evolve with time. More generally, our results imply an impact parameter "sweet spot" for atmospheric characterization, independent of the sign of the active region temperature contrast, whose location depends on the distribution of active regions. The distribution may be revealed by transit residuals as multiple planets probe different latitudes, while longitudes are sampled in time, such that the variance and frequency of the correlated scatter could constrain active-region filling factors, sizes, and separations.

astro-ph.EP↗

arXiv2026

Nautilus Space Observatory: Unveiling the Diversity and Origin of Sub-Neptunes with the Nautilus Space Observatory

Sub-Neptunes are the most common class of planets in the Galaxy, yet they have no Solar System analog and remain poorly understood as a population. JWST observations have revealed atmospheres spanning a wide range of metallicities, compositions, and cloud properties, driving active debates over whether warm sub-Neptunes harbor liquid water oceans beneath H2-rich envelopes, maintain stratified H2/H2O interiors, or have well-mixed, metal-rich envelopes. Open questions also remain over what physical processes drive transitions between hazy and clear atmospheres. These are intrinsically population-level questions that single-target observations, however deep, cannot resolve. Here we argue that a sub-Neptune population survey with the Nautilus Space Observatory, a proposed constellation of large-diameter space telescopes, would deliver the first statistical map of sub-Neptune atmospheric diversity, test competing classification schemes, identify habitable candidates, and serve as a pathfinder population for the eventual habitable-worlds search. These goals are achievable across the proposed mission classes for the constellation, and this architecture is uniquely well-matched to this science case since population-level questions demand sample size and a uniform observing strategy.

astro-ph.IM↗

arXiv2026

Mapping Stellar Heterogeneities with the Nautilus Space Observatory

Stellar photospheric heterogeneities, such as starspots and faculae, are a fundamental limitation for exoplanet transmission spectroscopy. Inhomogeneous surfaces can imprint wavelength-dependent signals during transits that may mimic or mask atmospheric absorption features, especially for planets orbiting cool low-mass stars. Recent work has shown that the information content of transmission spectroscopy observations can be sufficient to correct for stellar contamination, but only if stellar photosphere and active-region models have adequate fidelity. This requires empirical benchmarking with observations that validate next-generation stellar models and identify which spectral diagnostics best encode heterogeneity properties as a function of spectral type, activity level, and time. We propose a two-generation Nautilus program that leverages the scalable architecture of the observatory concept. Generation 1 would use broad-wavelength time-series observations of transiting exoplanet systems to connect starspot-crossing events and out-of-transit variability to localized and disk-integrated heterogeneity properties. Generation 2 would use the optimized spectral diagnostics identified in Generation 1 to conduct slitless spectroscopic monitoring of large samples of GKM stars on different timescales. Generation 2 instrumentation would include activity tracers of both the photosphere and chromosphere. This program would provide the benchmark data and population-level framework needed to turn stellar contamination into a calibrated input for exoplanet atmospheric retrievals.

astro-ph.IM↗

arXiv2026

Nautilus Space Observatory: The Evolution of Planets and their Atmospheres

We are just beginning to explore the billion-year evolution from nascent planets in disks to mature planetary systems. Recent discoveries hint at demographic and atmospheric differences between young planets and their Gyr-old counterparts, but current facilities are limited - particularly in their ability to conduct statistical atmospheric studies over a broad period range. This white paper outlines compelling science achievable with the Nautilus Space Observatory, a proposed constellation of large-diameter space telescopes. We identify four primary scientific objectives: (1) determining the timescales over which planets evolve into sub-Neptunes and super-Earths; (2) tracking the temporal evolution of atmospheric mass-loss rates; (3) characterizing the evolution of the atmospheric mean molecular weight and C/O ratio; and (4) identifying the emergence of Helium-dominated worlds. Answering these questions requires the high spatial resolution, broad-wavelength coverage, large effective area, and parallelized multiple units that Nautilus provides. By isolating the physical processes that govern the evolution of planets and their atmospheres, these science objectives directly support NASA's Cosmic Origins and Exoplanet Exploration Programs.

astro-ph.IM↗

arXiv2026

Nautilus: Fast Time-Resolved Spectroscopy of GKM Stellar Flares and Their Implications for Planetary Habitability

Low-mass GKM dwarfs are prime targets for finding habitable-zone Earth-sized planets, but their frequent flares, especially on M~dwarfs, can strongly affect planetary atmospheres through enhanced UV/XUV radiation and stellar proton events, which can drive complex photochemistry and accelerate atmospheric escape. Current atmospheric and habitability models of planets around low-mass stars often rely on simplified flare inputs, such as fixed-temperature blackbodies or approximate optical-to-UV/XUV conversions. However, recent observations show that M~dwarfs' flare temperatures and spectral shapes can vary significantly with flare energy, phase, and stellar type, and that optical-based flare observations may underestimate the flare energy in the UV. Time-resolved spectroscopic flare observations of G- and K-dwarfs also remain rare compared to those of M dwarfs. Here, we propose that the Nautilus Space Observatory concept can provide a unique opportunity to obtain fast-cadence, precisely flux-calibrated, moderate-resolution NUV-to-NIR spectroscopy of flares across a large sample of GKM dwarfs. These observations will measure the time-dependent flare energy budget from the near-UV/blue continuum to the optical and near-infrared continuum, while resolving key chromospheric lines that trace the underlying flare physics. We aim to construct a statistical library of empirical flare spectral templates organized by flare and stellar properties, including flare energy, flare phase, and host-star spectral type. This library will provide a practical bridge between observed stellar flare properties and the radiation inputs required for planetary atmospheric evolution and habitability simulations.

astro-ph.SR↗

arXiv2026

Overestimated Pressure Broadening Misleads Model Spectra in Cool M Dwarf Stars

Available one-dimensional stellar models fail to reproduce the observed spectrum of the ultracool M dwarf TRAPPIST-1. In particular, current models predict strong iron hydride (FeH) absorption due to the Wing-Ford bands at 0.99$\mu$m, yet this spectral feature is only weakly present in TRAPPIST-1 and other mid-to-late M dwarf stars. Additionally, the shape of the continuum between the water bands in the near-infrared does not match between models and observations. Here, we show that assumptions about pressure broadening, specifically van der Waals broadening, have a dramatic effect on modeled broadband spectral features. We use Merged Parallelized Simplified-ATLAS to generate synthetic spectra over a range of van der Waals broadening strengths, adopting 1D PHOENIX temperature-pressure structures. We find that minimal broadening best matches the observed FeH profile at 0.99$\mu$m and in the pseudocontinuum between the large water bands. These results suggest that broadening prescriptions derived for Sun-like stars are not valid for lower-mass stars and that pressure broadening for molecular lines in cool stellar atmospheres must be reevaluated. Refining pressure broadening treatments will improve the accuracy of M dwarf spectral models, enabling more reliable determinations of stellar properties and atmospheric compositions of planets orbiting M dwarfs.

astro-ph.SR↗

arXiv2025

JWST TRAPPIST-1 e/b Program: Motivation and first observations

One of the forefront goals in the field of exoplanets is the detection of an atmosphere on a temperate terrestrial exoplanet, and among the best suited systems to do so is TRAPPIST-1. However, JWST transit observations of the TRAPPIST-1 planets show significant contamination from stellar surface features that we are unable to confidently model. Here, we present the motivation and first observations of our JWST multi-cycle program of TRAPPIST-1 e, which utilize close transits of the airless TRAPPIST-1 b to model-independently correct for stellar contamination, with the goal of determining whether TRAPPIST-1 e has an Earth-like mean molecular weight atmosphere containing CO$_2$. We present our simulations, which show that with the 15 close transit observations, we will be able to detect this atmosphere on TRAPPIST-1 e at $\Delta\ln\,Z=5$ or greater confidence assuming we are able to correct for stellar contamination using the close transit observations. We also show the first three observations of our program. We find that our ability to correct for stellar contamination can be inhibited when strong stellar flares are present, as flares can break the assumption that the star does not change meaningfully between planetary transits. The cleanest observation demonstrates the removal of stellar contamination contribution through an increased preference for a flat line over the original TRAPPIST-1 e spectrum, but highlights how minor data analysis assumptions can propagate significantly when searching for small atmospheric signals. This is amplified when using the signals from multiple planets, which is important to consider as we continue our atmospheric search.

astro-ph.EP↗

arXiv2025

JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b

Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and non-transiting exoplanets, however the PIE technique requires empirical validation. Here we apply the PIE technique to a combination of JWST NIRSpec G395H transit and eclipse measurements of WASP-17b, a hot Jupiter orbiting an F-type star, obtained consecutively (0.5 phase or 1.8 days apart) as part of the JWST-TST program to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS). Using the in-eclipse measured stellar spectrum to circumvent the need for ultra-precise stellar models, we extract the first JWST nightside emission spectrum of WASP-17b using only transit and eclipse data thereby performing a controlled test of the PIE technique. From the WASP-17b nightside spectrum, we measure a nightside equilibrium temperature of $1005 \pm 256$ K and find tentative evidence for nightside SO2 absorption ($\ln B = 1.45$, $2.3\sigma$). In context with the dayside, the temperature of the nightside is consistent with (1) previous eclipse mapping findings that suggest relatively inefficient day-night heat transport, and (2) a non-zero bond albedo of $0.42^{+0.06}_{-0.10}$. SO2 on the nightside, if confirmed, would represent the first direct evidence for transport-induced chemistry, matching previous model predictions, and opening a new door into the 3D nature of giant exoplanets. Our results suggest that PIE is feasible with JWST/NIRSpec for two epochs separated in time by significantly less than the rotation period of the host star.

astro-ph.EP↗

arXiv2025

JWST-TST DREAMS: Sulfur dioxide in the atmosphere of the Neptune-mass planet HAT-P-26 b from NIRSpec G395H transmission spectroscopy

We present the James Webb Space Telescope (JWST) transmission spectrum of the exoplanet HAT-P-26 b (18.6 Earth masses, 6.33 Earth radii), based on a single transit observed with the JWST NIRSpec G395H grating. We detect water vapor (ln B = 4.1), carbon dioxide (ln B = 85.6), and sulfur dioxide (ln B = 13.5) with high confidence, along with marginal indications for hydrogen sulfide and carbon monoxide (ln B < 0.5). The detection of SO2 in a warm super-Neptune sized exoplanet (radius about 6 Earth radii) bridges the gap between previous detections in hot Jupiters and sub-Neptunes, highlighting the role of disequilibrium photochemistry across a broad range of exoplanet atmospheres, including those cooler than 1000 K. Our precise measurements of carbon, oxygen, and sulfur indicate an atmospheric metallicity of about 10 times solar and a sub-solar C/O ratio. Retrieved molecular abundances are consistent within 2 sigma with predictions from self-consistent models including photochemistry. The elevated CO2 abundance and possible H2S signal may also reflect sensitivities to the thermal structure, cloud properties, or additional disequilibrium processes such as vertical mixing. We compare the SO2 abundance in HAT-P-26 b with that of ten other JWST-observed giant exoplanets, and find a correlation with atmospheric metallicity. The trend is consistent with the prediction from Crossfield (2023), showing a steep rise in SO2 abundance at low metallicities, and a more gradual increase beyond 30 times solar. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

astro-ph.EP↗

arXiv2025

The Photochemical Plausibility of Warm Exo-Titans Orbiting M-Dwarf Stars

The James Webb Space Telescope (JWST) has begun to spectrally characterize small exoplanets orbiting M-dwarf stars, but interpretation of these spectra is ambiguous, with stellar, instrumental, or atmospheric origins possible for apparent spectral features. Consequently, interpretation of JWST small exoplanet spectra follows a Bayesian approach, with less theoretically plausible interpretations facing a higher burden of proof. Here, we use photochemical modeling to evaluate the plausibility of warm exo-Titans, exoplanets with N$_2$-CH$_4$ atmospheres analogous to Titan but orbiting closer to their host stars. Consideration of warm exo-Titans is motivated by arguments from planet formation, as well as tentative evidence from observations. Using TRAPPIST-1e as a case study, we show that the higher instellation experienced by warm exo-Titans reduces their CH$_4$ lifetime $\tau_{\text{CH}_{4}}$ relative to true Titan by orders of magnitude, reducing the probability of observing them. We constrain the $\tau_{\text{CH}_{4}}$ on a warm exo-Titan to be $\leq0.1\times$ (and most likely $\leq0.02\times$) true Titan, implying the absolute probability of detecting a warm exo-Titan is $<0.1$ and likely $<0.01$. This finding is consistent with recent JWST nondetections of CH$_4$-dominated atmospheres on warm terrestrial exoplanets. The low prior probability means that the standard of proof required to claim a warm exo-Titan detection is high, and we offer specific suggestions towards such a standard of proof. Observation of oxidized carbon species would corroborate a putative warm exo-Titan detection. Confirmed detection of warm exo-Titans would signal the need to fundamentally rethink our understanding of the structure, dynamics, and photochemistry of Titan-like worlds.

astro-ph.EP↗

arXiv2025

JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e

TRAPPIST-1 e is one of the very few rocky exoplanets that is both amenable to atmospheric characterization and that resides in the habitable zone of its star -- located at a distance from its star such that it might, with the right atmosphere, sustain liquid water on its surface. Here, we present a set of 4 JWST/NIRSpec PRISM transmission spectra of TRAPPIST-1 e obtained from mid to late 2023. Our transmission spectra exhibit similar levels of stellar contamination as observed in prior works for other planets in the TRAPPIST-1 system (Lim et al, 2023; Radica et al., 2024), but over a wider wavelength range, showcasing the challenge of characterizing the TRAPPIST-1 planets even at relatively long wavelengths (3-5 um). While we show that current stellar modeling frameworks are unable to explain the stellar contamination features in our spectra, we demonstrate that we can marginalize over those features instead using Gaussian Processes, which enables us to perform novel exoplanet atmospheric inferences with our transmission spectra. In particular, we are able to rule out cloudy, primary H$_2$-dominated ($\gtrsim$ 80$\%$ by volume) atmospheres at better than a 3$\sigma$ level. Constraints on possible secondary atmospheres on TRAPPIST-1 e are presented in a companion paper (Glidden et al., 2025). Our work showcases how JWST is breaking ground into the precisions needed to constrain the atmospheric composition of habitable-zone rocky exoplanets.

astro-ph.EP↗

arXiv2025

JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e

The TRAPPIST-1 system offers one of the best opportunities to characterize temperate terrestrial planets beyond our own solar system. Within the TRAPPIST-1 system, planet e stands out as highly likely to sustain surface liquid water if it possesses an atmosphere. Recently, we reported the first JWST/NIRSpec PRISM transmission spectra of TRAPPIST-1 e, revealing significant stellar contamination, which varied between the four visits. Here, we assess the range of planetary atmospheres consistent with our transmission spectrum. We explore a wide range of atmospheric scenarios via a hierarchy of forward modeling and retrievals. We do not obtain strong evidence for or against an atmosphere. Our results weakly disfavor CO$_2$-rich atmospheres for pressures corresponding to the surface of Venus and Mars and the cloud tops of Venus at 2$\sigma$. We exclude H$_2$-rich atmospheres containing CO$_2$ and CH$_4$ in agreement with past work, but find that higher mean molecular weight, N$_2$-rich atmospheres with trace CO$_2$ and CH$_4$ are permitted by the data. Both a bare rock and N$_2$-rich atmospheric scenario provide adequate fits to the data, but do not fully explain all features, which may be due to either uncorrected stellar contamination or atmospheric signals. Ongoing JWST observations of TRAPPIST-1 e, exploiting consecutive transits with TRAPPIST-1 b, will offer stronger constraints via a more effective stellar contamination correction. The present work is part of the JWST Telescope Scientist Team (JWST-TST) Guaranteed Time Observations, which is performing a Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

astro-ph.EP↗

arXiv2025

Warm, water-depleted rocky exoplanets with surface ionic liquids: A proposed class for planetary habitability

The discovery of thousands of exoplanets and the emergence of telescopes capable of exoplanet atmospheric characterization have intensified the search for habitable worlds. Due to selection biases, many exoplanets under study are planets deemed inhospitable because their surfaces are too warm to support liquid water. We propose that such planets could still support life through ionic liquids: Liquid salts with negligible vapor pressure that can persist on warm planets with thin atmospheres, where liquid water cannot. Ionic liquids have not previously been considered as naturally occurring substances, and thus have not been discussed in planetary science. We demonstrate in laboratory experiments that ionic liquids can form from planetary materials: Sulfuric acid combined with nitrogen-containing organic molecules. Sulfuric acid can be volcanic in origin, and organic compounds are commonly found on planetary bodies. The required planetary surface is water-depleted and must support sulfuric acid transiently in liquid phase to dissolve organics, followed by evaporation of excess liquid, conditions spanning approximately 300 K at 10^-7 atm to 350-470 K at 0.01 atm. Because ionic liquids have extremely low vapor pressures, they are not prone to evaporation, allowing small droplets or pools to persist without ocean-like reservoirs. Ionic liquids' minuscule vapor pressure at room temperature suggests possible stability on planets with negligible atmospheres, shielded by magnetic fields or rock crevices against harsh cosmic radiation. Ionic liquids can stably dissolve enzymes and other biomolecules, enabling biocatalysis and offering a plausible solvent for life, broadening the definition of habitable worlds.

astro-ph.EP↗

arXiv2024

JWST-TST DREAMS: A Precise Water Abundance for Hot Jupiter WASP-17b from the NIRISS SOSS Transmission Spectrum

Water has proven to be ubiquitously detected in near-infrared (NIR) transmission spectroscopy observations of hot Jupiter atmospheres, including WASP-17b. However, previous analyses of WASP-17b's atmosphere based upon Hubble Space Telescope (HST) and Spitzer data could not constrain the water abundance, finding that sub-solar, super-solar and bimodal posterior distributions were all statistically valid. In this work, we observe one transit of the hot Jupiter WASP-17b using JWST's Near Infrared Imager and Slitless Spectrograph Single Object Slitless Spectroscopy (NIRISS SOSS) mode. We analyze our data using three independent data analysis pipelines, finding excellent agreement between results. Our transmission spectrum shows multiple H$_2$O absorption features and a flatter slope towards the optical than seen in previous HST observations. We analyze our spectrum using both PICASO+Virga forward models and free retrievals. POSEIDON retrievals provide a well-constrained super-solar $\log$(H$_2$O) abundance (-2.96$^{+0.31}_{-0.24}$), breaking the degeneracy from the previous HST/Spitzer analysis. We verify our POSEIDON results with petitRADTRANS retrievals. Additionally, we constrain the abundance of $\log$(H$^-$), -10.19$^{+0.30}_{-0.23}$, finding that our model including H$^-$ is preferred over our model without H$^-$ to 5.1 $\sigma$. Furthermore, we constrain the $\log$(K) abundance (-8.07$^{+0.58}_{-0.52}$) in WASP-17b's atmosphere for the first time using space-based observations. Our abundance constraints demonstrate the power of NIRISS SOSS's increased resolution, precision, and wavelength range to improve upon previous NIR space-based results. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

astro-ph.EP↗

arXiv2024

Reliable Transmission Spectrum Extraction with a Three-Parameter Limb Darkening Law

Stellar limb darkening must be properly accounted for to accurately determine the radii of exoplanets at various wavelengths. The standard approach to address limb darkening involves either using laws with coefficients from modelled stellar spectra or determining the coefficients empirically during light curve fitting of the data. Here, we test how accurately three common laws -- quadratic, power, and a three-parameter law -- can reproduce stellar limb darkening at different wavelengths and across a broad range of stars. We show that using a quadratic limb darkening law, which is most frequently employed by the community, leads to wavelength-dependent offsets in retrieved transmission spectra. For planets with high impact parameters ($b$ larger than about 0.5) the amplitude of these offsets can reach 1\% of the transit depth which is some cases is comparable to and can even exceed the expected signals from the planetary atmosphere. Furthermore, the quadratic law causes an offset in the value of the impact parameter when it is determined by fitting the broadband transit light curves. In contrast, using the Kipping--Sing three-parameter law leads to robust retrievals. We advocate the use of this law in retrievals, especially for transits with large impact parameters.

astro-ph.EP↗

arXiv2024

JWST-TST DREAMS: A Super-Solar Metallicity in WASP-17 b Dayside Atmosphere from NIRISS SOSS Eclipse Spectroscopy

We present the first emission spectrum of the hot Jupiter WASP-17 b using one eclipse observation from the JWST Near Infrared Imager and Slitless Spectrograph (NIRISS) Single Object Slitless Spectroscopy (SOSS) mode. Covering a wavelength range of 0.6 to 2.8 microns, our retrieval analysis reveals a strong detection of H2O in WASP-17b dayside atmosphere (6.4sigma). Our retrievals consistently favor a super-solar dayside H2O abundance and a non-inverted temperature-pressure profile over a large pressure range. Additionally, our examination of the brightness temperature reveals excess emission below 1 microns, suggesting the possibility of a high internal temperature (600 to 700 K) and/or contributions from reflected light. We highlight that JWST emission spectroscopy retrieval results can be sensitive to whether negative eclipse depths are allowed at optical wavelengths during light curve fitting. Our findings deepen our understanding of WASP-17b atmospheric composition while also highlighting the sensitivity of our results to pressure-temperature profile parameterizations. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

astro-ph.EP↗

arXiv2024

JWST-TST DREAMS: Non-Uniform Dayside Emission for WASP-17b from MIRI/LRS

We present the first spectroscopic characterisation of the dayside atmosphere of WASP-17b in the mid-infrared using a single JWST MIRI/LRS eclipse observation. From forward-model fits to the 5-12 $\mu$m emission spectrum, we tightly constrain the heat redistribution factor of WASP-17b to be 0.92$\pm$0.02 at the pressures probed by this data, indicative of inefficient global heat redistribution. We also marginally detect a supersolar abundance of water, consistent with previous findings for WASP-17b, but note our weak constraints on this parameter. These results reflect the thermodynamically rich but chemically poor information content of MIRI/LRS emission data for high-temperature hot Jupiters. Using the eclipse mapping method, which utilises the signals that the spatial emission profile of an exoplanet imprints on the eclipse light curve during ingress/egress due to its partial occultation by the host star, we also construct the first eclipse map of WASP-17b, allowing us to diagnose its multidimensional atmospheric dynamics for the first time. We find a day-night temperature contrast of order 1000 K at the pressures probed by this data, consistent with our derived heat redistribution factor, along with an eastward longitudinal hotspot offset of $18.7^{+11.1\deg}_{-3.8}$, indicative of the presence of an equatorial jet induced by day-night thermal forcing being the dominant redistributor of heat from the substellar point. These dynamics are consistent with general circulation model predictions for WASP-17b. This work is part of a series of studies by the JWST Telescope Scientist Team (JWST-TST), in which we use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

astro-ph.EP↗

arXiv2024

Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres?

Isotopologue ratios are anticipated to be one of the most promising signs of life that can be observed remotely. On Earth, carbon isotopes have been used for decades as evidence of modern and early metabolic processes. In fact, carbon isotopes may be the oldest evidence for life on Earth, though there are alternative geological processes that can lead to the same magnitude of fractionation. However, using isotopologues as biosignature gases in exoplanet atmospheres presents several challenges. Most significantly, we will only have limited knowledge of the underlying abiotic carbon reservoir of an exoplanet. Atmospheric carbon isotope ratios will thus have to be compared against the local interstellar medium or, better yet, their host star. A further substantial complication is the limited precision of remote atmospheric measurements using spectroscopy. The various metabolic processes which cause isotope fractionation cause less fractionation than anticipated measurement precision (biological fractionation is typically 2 to 7%). While this level of precision is easily reachable in the laboratory or with special in situ instruments, it is out of reach of current telescope technology to measure isotope ratios for terrestrial exoplanet atmospheres. Thus, gas isotopologues are poor biosignatures for exoplanets given our current and foreseeable technological limitations.

astro-ph.EP↗