Showing 1–49 of 49 results for author: May, E M

GEMS JWST: Hold on to your HATS(-6 b), a sub-solar metallicity giant planet with water, methane and ammonia in its atmosphere

Authors: Giannina Guzmán Caloca, Caleb I. Cañas, Nicole L. Wallack, Erin M. May, Shang-Min Tsai, Simon Müller, Ravit Helled, Shubham Kanodia, Jacob Lustig-Yaeger, Knicole D. Colón, Ian Czekala, Megan Delamer, Peter Gao, Te Han, Jessica Libby-Roberts, Suvrath Mahadevan, Anjali A. A. Piette, Guðmundur Stefánsson, Kevin B. Stevenson

Abstract: HATS-6 b is one of several recently discovered Giant Exoplanets orbiting M-dwarf Stars (GEMS) and is part of a JWST survey that aims to compare bulk and atmospheric properties of these rare planets against their FGK star counterparts. HATS-6 b is a warm ($\mathrm{T_{eq}}\sim700$ K), Saturn-mass ($M_p\sim0.3~\mathrm{M_J}$), Jupiter-radius ($R_p\sim1~\mathrm{R_J}$) planet that transits its star ever… ▽ More HATS-6 b is one of several recently discovered Giant Exoplanets orbiting M-dwarf Stars (GEMS) and is part of a JWST survey that aims to compare bulk and atmospheric properties of these rare planets against their FGK star counterparts. HATS-6 b is a warm ($\mathrm{T_{eq}}\sim700$ K), Saturn-mass ($M_p\sim0.3~\mathrm{M_J}$), Jupiter-radius ($R_p\sim1~\mathrm{R_J}$) planet that transits its star every $\sim$ 3 days. In this study, we present the transmission spectrum of HATS-6 b obtained with two transits using the PRISM mode of JWST Near Infrared Spectrograph (NIRSpec), spanning a wavelength range of $0.6-5.3$ um. Analyzing these JWST observations using an iterative approach between forward modeling and free chemistry retrievals, we derive a low metallicity ($\log\mathrm{[M/H]}=-1.99^{+0.2}_{-0.2}$) sub-solar C/O ($\log\mathrm{[C/O]=-0.46^{+0.2}_{-0.2}}$) atmosphere, and find strong evidence for H$_2$O, CH$_4$, and NH$_3$ at volume mixing ratios (in $\log[X]$) of $-4.88_{-0.24}^{+0.25}$, $-5.38_{-0.19}^{+0.18}$, and $-6.03_{-0.19}^{+0.18}$, respectively. We consistently retrieve a significantly lower $\mathrm{T_{eq}}$ than predicted from the orbital configuration of HATS-6 b, which was impervious to any data reduction and retrieval choices, suggesting a non-zero bond albedo. Our planetary interior models retrieve bulk metallicities three orders of magnitude larger than our retrieved atmospheric metallicity, also suggesting that the atmosphere is not well-mixed. We find an excess feature around 3 um, and expand on possible explanations for this, such as the presence of HCN or hydrocarbons like C$_2$H$_4$. Yet, due to the degeneracies present for hydrocarbon features in this wavelength region, we do not draw any conclusions about the excess feature and instead encourage further observations and follow-up of this intriguing target. △ Less

Submitted 17 August, 2026; originally announced August 2026.

Comments: 33 pages excluding appendices, 33 figures, 8 tables, 10 appendices, accepted for publication in AJ

Precise Determination of the Metallicity and C/O of WASP-39~b From a Single JWST Instrument Mode with Phase-Resolved Cross-Correlation Retrievals

Authors: Arjun B. Savel, Eliza M. -R. Kempton, Erin M. May, Matthew C. Nixon, Jegug Ih, Katherine A. Bennett, Joost P. Wardenier

Abstract: Measuring atmospheric metallicities and C/O ratios is a key goal of JWST exoplanet science, given their proposed link to planet formation. Achieving this goal has previously been shown to require broad wavelength coverage ($\sim$1--5 $μ$m), typically demanding multiple instrument modes to complete the molecular inventory. Here, we show that the multi-instrument requirement can be circumvented usin… ▽ More Measuring atmospheric metallicities and C/O ratios is a key goal of JWST exoplanet science, given their proposed link to planet formation. Achieving this goal has previously been shown to require broad wavelength coverage ($\sim$1--5 $μ$m), typically demanding multiple instrument modes to complete the molecular inventory. Here, we show that the multi-instrument requirement can be circumvented using phase-resolved cross-correlation retrievals at native pixel resolution -- an approach more typically applied to ground-based high-resolution spectroscopy. By applying this novel analysis technique to an archival single-mode transit of the hot Jupiter WASP-39~b obtained with NIRSpec/G395H, we detect and obtain bounded abundances for all of its major carbon- and oxygen-bearing molecules: H$_2$O ($Δ\ln(Z) = 67$), CO ($Δ\ln(Z) = 25$), CO$_2$ ($Δ\ln(Z) = 475$), and SO$_2$ ($Δ\ln(Z) = 10$). Notably, while standard retrieval methods fail to detect CO in these same data ($Δ\ln(Z) = 0.2$), our approach detects it decisively, confirming it as the dominant carbon carrier in WASP-39 b's atmosphere. From these abundances, we robustly derive a metallicity of $\rm [(C + O) / H] = 1.2 \pm 0.2$ and a C/O ratio of $0.68^{+0.10}_{-0.14} $, generally consistent with previous multi-instrument analyses. In comparison, traditional retrievals performed on the G395H data alone produce biased and inaccurate values of both parameters, driven primarily by the non-detection of CO as well as incomplete water band coverage. Our results establish phase-resolved cross-correlation retrievals as a powerful tool for extracting maximum atmospheric information from existing and future JWST data sets. △ Less

Submitted 20 July, 2026; originally announced July 2026.

Comments: Submitted to AAS Journals. 16 pages, 7 figures, 1 table. Comments welcome!

Mitigating Charge Migration in JWST NIRISS Reveals That KELT-7 b is a Metal-enriched Ultra-hot Jupiter Orbiting a Young Metal-rich Star

Authors: Stephen P. Schmidt, Erin M. May, Joshua D. Lothringer, Patrick McCreery, Mei Ting Mak, Myles Pope, Harry Baskett, Sagnick Mukherjee, David K. Sing, Katherine A. Bennett, Arika Egan, Guangwei Fu, Daniel P. Thorngren, Duncan A. Christie, Carlos Gascón, Le-Chris Wang, Lakeisha M. Ramos Rosado, Nathan J. Mayne, Natalie H. Allen, Zafar Rustamkulov, Mercedes López-Morales, Kevin C. Schlaufman

Abstract: We present the first panchromatic JWST transmission spectrum of an ultra-hot Jupiter, combining NIRISS and NIRSpec observations to constrain KELT-7\,b's atmospheric properties. We show evidence for charge migration in our NIRISS SOSS observation between 1--1.5~$μ$m, a wavelength range crucial to test for enhanced H$^-$ previously inferred from HST WFC3/IR G141 observations. We mitigate charge migr… ▽ More We present the first panchromatic JWST transmission spectrum of an ultra-hot Jupiter, combining NIRISS and NIRSpec observations to constrain KELT-7\,b's atmospheric properties. We show evidence for charge migration in our NIRISS SOSS observation between 1--1.5~$μ$m, a wavelength range crucial to test for enhanced H$^-$ previously inferred from HST WFC3/IR G141 observations. We mitigate charge migration by fitting the ramp after extracting 1D stellar spectra at the group level. This ``late-ramp-fit'' method accurately calculates KELT-7\,b's transmission spectrum between 1--1.5~$μ$m at higher signal-to-noise. Using the transit-derived stellar mean density during stellar property inference reveals that KELT-7 is a $640\pm100$ Myr-old, $[\text{Fe}/\text{H}]=0.46\pm0.02$ star. Combined with NIRSpec and re-reduced WFC3/UVIS G280 data, our free retrieval analysis shows strong evidence for H$_2$O, CO$_2$, and TiO among high-temperature species, but not H$^-$ or clouds. Unaccounted-for systematics may therefore bias longer-wavelength WFC3/IR G141 transit depths shallower. Our free retrieval, two equilibrium retrievals, and self-consistent grid fit all prefer a high metallicity but find discrepant C/O ratios. Agglomerated together, we constrain a super-stellar $\text{M/H}=92^{+24}_{-23}\times$~Solar and C/O~$\leq0.9$, suggesting enhanced metal accretion in the later stages of KELT-7\,b's formation. Our GCMs explain the observed lack of limb asymmetry with superrotating jet-driven efficient horizontal mixing. The stark contrast between our panchromatic analysis and prior analyses on subsets of these data demonstrates the value of broad wavelength coverage for the comprehensive study of exoplanet atmospheres. △ Less

Submitted 7 July, 2026; originally announced July 2026.

Comments: 38 pages, 20 figures, 7 tables. Submitted to AAS Journals - comments welcome!

Aerosols and hydrocarbons in the atmosphere of a white dwarf planet

Authors: Ryan J. MacDonald, Christopher E. O'Connor, Victoria A. Boehm, E. M. May, David K. Sing, Elijah Mullens, L. C. Mayorga, Trevor O. Foote, Simon Blouin, Logan A. Pearce, Nikole K. Lewis, Jeff Valenti, Natasha E. Batalha, Maura Lally, Joshua D. Lothringer, Mark S. Marley, Ishan Mishra, Susan E. Mullally

Abstract: Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs. Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets can survive the stellar post-main-sequence stage intact. Little is known about the atmospheric composition of post-main-sequence planets, with the most evolved transiting planets with atmospheri… ▽ More Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs. Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets can survive the stellar post-main-sequence stage intact. Little is known about the atmospheric composition of post-main-sequence planets, with the most evolved transiting planets with atmospheric detections to date orbiting subgiants. Here we report an atmospheric detection for the white dwarf planet WD 1856 b, achieved through transmission spectroscopy with the JWST NIRSpec PRISM. Our 0.5-5.0 $μ$m spectrum reveals the presence of hydrocarbons (odds ratio of $167:1$ to $5377:1$, with $\mathrm{CH}_4$ preferred at $17:1$ to $30:1$), aerosols ($2 \times 10^5:1$ to $2 \times 10^6:1$), and thermal emission from the planetary nightside ($2 \times 10^{63}:1$ to $2 \times 10^{73}:1$). Our spectral analysis constrains WD 1856 b's mass to $4.3$ to $10.9 \mathrm{M}_J$, finds a carbon-enriched atmosphere (with a $\mathrm{CH}_4$ abundance of $\approx 7\%$), and an effective temperature exceeding the expected planetary equilibrium temperature ($390$ to $412 \, \mathrm{K}$ vs. $160 \, \mathrm{K}$). Based on cooling models, these results suggest that WD 1856 b underwent a migration-related reheating event $3.0$ to $5.5 \, \mathrm{Gyr}$ into the white dwarf phase, consistent with post-main-sequence tidal evolution to the present-day $0.02 \, \mathrm{au}$ circular orbit. Our results provide a window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun. △ Less

Submitted 1 July, 2026; originally announced July 2026.

Comments: 28 pages, 12 figures, 3 tables. Published in Nature (1 July 2026). Accepted manuscript, for the version of record see: https://www.nature.com/articles/s41586-026-10514-7

Journal ref: Nature 655, 76-80 (2026)

Additional JWST/NIRSpec Transits of the Rocky M Dwarf Exoplanet GJ 1132 b Reveal a Featureless Spectrum

Authors: Katherine A. Bennett, Ryan J. MacDonald, Sarah Peacock, Junellie Perez, E. M. May, Sarah E. Moran, Lili Alderson, Jacob Lustig-Yaeger, Hannah R. Wakeford, David K. Sing, Kevin B. Stevenson, Natasha E. Batalha, Mercedes López-Morales, Munazza K. Alam, Joshua D. Lothringer, Guangwei Fu, James Kirk, Jeff A. Valenti, L. C. Mayorga, Kristin S. Sotzen

Abstract: As an archetypal M-dwarf rocky exoplanet, GJ 1132 b has a varied history of atmospheric measurements. At 1.13 $\rm R_{\oplus}$, 1.66 $\rm M_{\oplus}$, and 580 K, it orbits a bright, slowly rotating M dwarf in a 1.6-day period, making it a prime target for characterization. In this study, we combine two JWST NIRSpec/G395H transits previously reported by May and MacDonald et al. 2023 with two new NI… ▽ More As an archetypal M-dwarf rocky exoplanet, GJ 1132 b has a varied history of atmospheric measurements. At 1.13 $\rm R_{\oplus}$, 1.66 $\rm M_{\oplus}$, and 580 K, it orbits a bright, slowly rotating M dwarf in a 1.6-day period, making it a prime target for characterization. In this study, we combine two JWST NIRSpec/G395H transits previously reported by May and MacDonald et al. 2023 with two new NIRSpec/G395M transits to constrain the presence of an atmosphere. This marks the first time the G395H and G395M modes have been combined for a single target, and we report no difference in the quality of data between the two modes. For rocky M-dwarf studies, G395H may still be preferred if stacking transits to utilize the high-resolution flux-calibrated stellar spectra and assess evolving stellar heterogeneity. GJ 1132 b's co-added transmission spectrum is best-fit with a flat line. A thin steam atmosphere is also consistent with the data, but this interpretation is driven almost entirely by the first transit, which suggests an increase in cool spot coverage-fraction derived from the flux-calibrated stellar spectra. This demonstrates the importance of always considering stellar heterogeneity evolution in multi-visit transits, and also the importance of a "leave-one-transit-out" approach in modeling efforts of co-added transits. We combine these results with MIRI/LRS emission data (Xue et al. 2024) to show that together, transmission and emission are consistent with only the thinnest of atmospheres. Given GJ 1132 b's age and distance from the star, a thin atmosphere is not likely stable. Therefore, the simplest explanation is that GJ 1132 b is indeed a bare rock. △ Less

Submitted 14 August, 2025; originally announced August 2025.

Comments: Accepted for publication in AJ. Data products available on Zenodo

K2-18b Does Not Meet The Standards of Evidence For Life

Authors: Kevin B. Stevenson, Jacob Lustig-Yaeger, E. M. May, Ravi K. Kopparapu, Thomas J. Fauchez, Jacob Haqq-Misra, Mary Anne Limbach, Edward W. Schwieterman, Kristin S. Sotzen, Shang-Min Tsai

Abstract: K2-18b, a temperate sub-Neptune, has garnered significant attention due to claims of possible biosignatures in its atmosphere. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked considerable debate, primarily around arguments that their absorption features are not uniquely identifiable. Here, we consider all five questions from the astrobiology standa… ▽ More K2-18b, a temperate sub-Neptune, has garnered significant attention due to claims of possible biosignatures in its atmosphere. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked considerable debate, primarily around arguments that their absorption features are not uniquely identifiable. Here, we consider all five questions from the astrobiology standards of evidence framework, starting with: Have we detected an authentic signal? To answer this, we analyzed publicly-available JWST observations of K2-18b using independent data reduction and spectral retrieval methodologies. Our comprehensive set of reductions demonstrates that the MIRI transit spectrum is highly susceptible to unresolved instrumental systematics. Applying different wavelength binning schemes yields a potpourri of planet spectra that then lead to a wide assortment of atmospheric interpretations. Consequently, we offer recommendations to help minimize this previously-underappreciated instrument systematic in future MIRI reductions of any exoplanet. While the MIRI binning scheme adopted by Madhusudhan et al. (2025) favors the presence of DMS/DMDS in K2-18b, we find that 87.5% of retrievals using our preferred MIRI binning scheme do not. When considering the full, 0.7 - 12 micron transit spectrum, we confirm the detection of CH4 and favor CO2, and find the presence of DMS and C2H4 to be interchangeable. Moreover, we find that the tentative presence of large features in the MIRI transit spectrum is in tension with the more robust, yet smaller, features observed in the near IR. We conclude that red noise -- rather than an astrophysical signal -- plagues the mid-IR data and there is, as yet, no statistically significant evidence for biosignatures in the atmosphere of K2-18b. △ Less

Submitted 3 September, 2025; v1 submitted 7 August, 2025; originally announced August 2025.

Comments: Accepted for publication in AJ

Characterizing the Dynamics and Chemistry of Transiting Exoplanets with the Habitable World Observatory

Authors: Hannah R. Wakeford, Laura C. Mayorga, Joanna K. Barstow, Natasha E. Batalha, Ludmila Carone, Sarah L. Casewell, Theodora Karalidi, Tiffany Kataria, Erin M. May, Michiel Min

Abstract: The primary scientific objective of this Habitable Worlds Observatory (HWO) Science Case Development Document (SCDD) is to measure planetary rotation rates of transiting exoplanets to determine the structure, composition, circulation, and aerosol properties of their planetary atmospheres. For this analysis, HWO would obtain spectroscopic phase curves for planets with orbital periods of 5 - 20+ day… ▽ More The primary scientific objective of this Habitable Worlds Observatory (HWO) Science Case Development Document (SCDD) is to measure planetary rotation rates of transiting exoplanets to determine the structure, composition, circulation, and aerosol properties of their planetary atmospheres. For this analysis, HWO would obtain spectroscopic phase curves for planets with orbital periods of 5 - 20+ days, to assess tidal locking radius assumptions. Extending phase curve studies out to longer orbital periods than accessible with current and near-future telescopes will enable detailed investigation of atmospheric structure, composition, and circulation for planets that are much cooler than the more highly irradiated planets accessible with JWST phase curve observations (i.e., Teq < 500 K for HWO versus 1400 K <= Teq <= 2600 K for JWST). Broad wavelength coverage extending from the UV to the NIR would capture both reflected light and thermal emission, enabling HWO to conduct comprehensive characterization of planetary atmospheres. UV observations would probe high altitudes, thereby providing valuable insights into atmospheric (dis)equilibrium, aerosol properties, and the effects of photochemical processes on atmospheric composition. We also discuss the role of polarimetry in the classification of aerosols and the associated role they play in the atmospheric energy budget that directly ties them to the chemistry and circulation structure of the atmosphere. △ Less

Submitted 28 June, 2025; originally announced June 2025.

Comments: Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology SCDD, to be presented at HWO2025 and submitted to Astronomical Society of the Pacific following community comments. Feedback welcomed

Cloudy mornings and clear evenings on a gas giant exoplanet

Authors: Sagnick Mukherjee, David K. Sing, Guangwei Fu, Kevin B. Stevenson, Stephen P. Schmidt, Harry Baskett, Mei Ting Mak, Patrick McCreery, Natalie H. Allen, Katherine A. Bennett, Duncan A. Christie, Carlos Gascón, Jayesh Goyal, Éric Hébrard, Joshua D. Lothringer, Mercedes López-Morales, Jacob Lustig-Yaeger, Erin M. May, L. C. Mayorga, Nathan Mayne, Lakeisha M. Ramos Rosado, Henrique Reggiani, Zafar Rustamkulov, Kevin C. Schlaufman, K. S. Sotzen , et al. (3 additional authors not shown)

Abstract: The spectra of exoplanet atmospheres are affected by aerosols (clouds and hazes) of uncertain origin. Proposed aerosol formation mechanisms include gas condensation or photochemical reactions. We measure the transmission spectrum of the tidally locked gas giant exoplanet WASP-94A b and identify asymmetry in its atmosphere. The morning limb is cooler and cloudy, while the evening limb is hotter and… ▽ More The spectra of exoplanet atmospheres are affected by aerosols (clouds and hazes) of uncertain origin. Proposed aerosol formation mechanisms include gas condensation or photochemical reactions. We measure the transmission spectrum of the tidally locked gas giant exoplanet WASP-94A b and identify asymmetry in its atmosphere. The morning limb is cooler and cloudy, while the evening limb is hotter and exhibits gaseous H$_2$O absorption features. We interpret this difference as due to the formation of cloud droplets near the morning limb, which evaporate during circulation to the evening limb. The dominant aerosols are clouds cycling between the day and night sides of the atmosphere, not photochemical hazes. The resulting asymmetry can severely bias chemical abundance measurements, unless limb-resolved spectroscopy is available. △ Less

Submitted 22 May, 2026; v1 submitted 16 May, 2025; originally announced May 2025.

Comments: This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science on 21st May, 2026, DOI: 10.1126/science.adx5903

Journal ref: Science, 21 May 2026, Vol 392, Issue 6800, pp. 858-862

An Analysis of Spitzer Phase Curves for WASP-121b and WASP-77Ab

Authors: Brian Davenport, Thomas Kennedy, E. M. May, Emily Rauscher, Eliza M. -R. Kempton, Isaac Malsky, Kevin B. Stevenson, Jacob L. Bean, Megan Weiner Mansfield

Abstract: We present analyses of Spitzer InfraRed Array Camera (IRAC) 3.6 $μ$m and 4.5 $μ$m phase curve observations of hot Jupiters WASP-77Ab and WASP-121b. For WASP-121b, we find amplitudes of 1771 $\pm$ 95 ppm (3.6 $μ$m) and 2048 $\pm$ 109 ppm (4.5 $μ$m), and near-zero offsets of -0.78 $\pm$ 1.87$^{\circ}$ (3.6 $μ$m) and 0.42 $\pm$ 1.74$^{\circ}$ (4.5 $μ$m), consistent within 2.2$σ$ and 1.3$σ$, respectiv… ▽ More We present analyses of Spitzer InfraRed Array Camera (IRAC) 3.6 $μ$m and 4.5 $μ$m phase curve observations of hot Jupiters WASP-77Ab and WASP-121b. For WASP-121b, we find amplitudes of 1771 $\pm$ 95 ppm (3.6 $μ$m) and 2048 $\pm$ 109 ppm (4.5 $μ$m), and near-zero offsets of -0.78 $\pm$ 1.87$^{\circ}$ (3.6 $μ$m) and 0.42 $\pm$ 1.74$^{\circ}$ (4.5 $μ$m), consistent within 2.2$σ$ and 1.3$σ$, respectively, with JWST NIRSpec results. For WASP-77Ab, we find amplitudes of 535 $\pm$ 52 ppm (3.6 $μ$m) and 919 $\pm$ 40 ppm (4.5 $μ$m), and offsets of 33.45 $\pm$ 2.79$^{\circ}$ (3.6 $μ$m) and 16.28 $\pm$ 2.52$^{\circ}$ (4.5 $μ$m). We report day- and nightside brightness temperatures: for WASP-121b, 2779 $\pm$ 40 K (3.6 $μ$m) and 2905 $\pm$ 51 K (4.5 $μ$m) (day) and 1259 $\pm$ 67 K (3.6 $μ$m) and 1349 $\pm$ 54 K (4.5 $μ$m) (night), and for WASP-77Ab, 1876 $\pm$ 23 K (3.6 $μ$m) and 1780 $\pm$ 25 K (day) and 1501 $\pm$ 22 K (3.6 $μ$m) and 1234 $\pm$ 20 K (4.5 $μ$m) (night). Comparing WASP-121b data to general circulation models, we find evidence for drag inhibiting day-to-night heat transfer, which our model reproduces using magnetic circulation. Further, comparing both planets' data to Energy Balance Models, we show suppressed circulation in WASP-121b and potential evidence for an unusually high Bond albedo in WASP-77Ab. We add both planets to the Spitzer population study of previously identified trends in offset versus orbital period, finding that a positive trend is weakened, but not eliminated, by including these planets. △ Less

Submitted 16 March, 2025; originally announced March 2025.

Comments: 17 pages, 11 figures, accepted for publication in The Astronomical Journal

GEMS JWST: Transmission spectroscopy of TOI-5205b reveals significant stellar contamination and a metal-poor atmosphere

Authors: Caleb I. Cañas, Jacob Lustig-Yaeger, Shang-Min Tsai, Simon Müller, Ravit Helled, Dana R. Louie, Giannina Guzmán Caloca, Shubham Kanodia, Peter Gao, Jessica Libby-Roberts, Kevin K. Hardegree-Ullman, Knicole D. Colón, Ian Czekala, Megan Delamer, Te Han, Andrea S. J. Lin, Suvrath Mahadevan, Erin M. May, Joe P. Ninan, Anjali A. A. Piette, Guðmundur Stefánsson, Kevin B. Stevenson, Johanna Teske, Nicole L. Wallack

Abstract: Recent discoveries of transiting giant exoplanets ($R_p\gtrsim8\mathrm{~R_\oplus}$) around M dwarfs (GEMS) present an opportunity to investigate their atmospheric compositions and explore how such massive planets form around low-mass stars contrary to the prediction from formation models. We present the first transmission spectra of TOI-5205b, a short-period ($P=1.63~\mathrm{days}$) Jupiter-like p… ▽ More Recent discoveries of transiting giant exoplanets ($R_p\gtrsim8\mathrm{~R_\oplus}$) around M dwarfs (GEMS) present an opportunity to investigate their atmospheric compositions and explore how such massive planets form around low-mass stars contrary to the prediction from formation models. We present the first transmission spectra of TOI-5205b, a short-period ($P=1.63~\mathrm{days}$) Jupiter-like planet ($M_p=1.08~\mathrm{M_J}$ and $R_p=0.94~\mathrm{R_J}$) orbiting an M4 dwarf ($M_\star=0.392~\mathrm{M_\odot}$, $R_\star=0.394~\mathrm{R_\odot}$). We obtained three transits using the PRISM mode of the JWST Near Infrared Spectrograph (NIRSpec) spanning $0.6-5.3$ um. The data reveal significant stellar contamination that is evident in the light curves as spot-crossing events and in the transmission spectra as a larger transit depth at bluer wavelengths. Atmospheric retrievals demonstrate that stellar contamination from unocculted starspots and faculae is the dominant component of the transmission spectrum at wavelengths $λ\lesssim3.0$ um, reducing the sensitivity to the presence of clouds or hazes in our models and preventing detection of $\mathrm{H_2O}$. The wavelength coverage enabled a robust detection of $\mathrm{CH_4}$ and $\mathrm{H_2S}$, which have detectable molecular features between $3.0-5.0$ um. For both clear or cloudy atmospheres, Bayesian retrievals consistently favored an atmosphere with sub-solar metallicity ($3σ$ upper limit of $\log\mathrm{[M/H]}\lesssim-1.24$) and super-solar C/O ratio ($3σ$ lower limit of $\log\mathrm{[C/O]}\gtrsim0.09$), although this may partly be driven by the non-detection of water due to stellar contamination. Planetary interior models predict a bulk metallicity of 10--20\%, which is larger than the atmospheric metallicity and suggests that the interior of TOI-5205b is decoupled from its atmosphere. △ Less

Submitted 25 February, 2026; v1 submitted 10 February, 2025; originally announced February 2025.

Comments: 29 pages + appendix, 23 figures including 6 figure sets, 13 tables, data behind the figures will appear in journal, accepted for publication in AJ. Updates from first version: improvements to the spot fitting and associated retrievals. Updates from second version: abstract revised to satisfy journal word limit

Journal ref: AJ 171 260 (2026)

A Comprehensive Reanalysis of K2-18 b's JWST NIRISS+NIRSpec Transmission Spectrum

Authors: Stephen P. Schmidt, Ryan J. MacDonald, Shang-Min Tsai, Michael Radica, Le-Chris Wang, Eva-Maria Ahrer, Taylor J. Bell, Chloe Fisher, Daniel P. Thorngren, Nicholas Wogan, Erin M. May, Piero Ferrari, Katherine A. Bennett, Zafar Rustamkulov, Mercedes López-Morales, David K. Sing

Abstract: Sub-Neptunes are the most common type of planet in our galaxy. Interior structure models suggest that the coldest sub-Neptunes could host liquid water oceans underneath their hydrogen envelopes -- sometimes called ``hycean'' planets. JWST transmission spectra of the $\sim$ 250 K sub-Neptune K2-18 b were recently used to report detections of CH$_4$ and CO$_2$, alongside weaker evidence of (CH$_3$)… ▽ More Sub-Neptunes are the most common type of planet in our galaxy. Interior structure models suggest that the coldest sub-Neptunes could host liquid water oceans underneath their hydrogen envelopes -- sometimes called ``hycean'' planets. JWST transmission spectra of the $\sim$ 250 K sub-Neptune K2-18 b were recently used to report detections of CH$_4$ and CO$_2$, alongside weaker evidence of (CH$_3$)$_2$S (dimethyl sulfide, or DMS). Atmospheric CO$_2$ was interpreted as evidence for a liquid water ocean, while DMS was highlighted as a potential biomarker. However, these notable claims were derived using a single data reduction and retrieval modeling framework, which did not allow for standard robustness tests. Here we present a comprehensive reanalysis of K2-18 b's JWST NIRISS SOSS and NIRSpec G395H transmission spectra, including the first analysis of the second-order NIRISS SOSS data. We incorporate multiple well-tested data reduction pipelines and retrieval codes, spanning 60 different data treatments and over 250 atmospheric retrievals. We confirm the detection of CH$_4$ ($\approx 4σ$), with a volume mixing ratio range $-2.14 \leq \log_{10} \mathrm{CH_4} \leq -0.53$, but we find no statistically significant or reliable evidence for CO$_2$ or DMS. Finally, we assess the retrieved atmospheric composition using photochemical-climate and interior models, demonstrating that our revised composition of K2-18\,b can be explained by an oxygen-poor mini-Neptune without requiring a liquid water surface or life. △ Less

Submitted 29 August, 2025; v1 submitted 30 January, 2025; originally announced January 2025.

Comments: 42 pages, 21 figures. Revised version; accepted to AJ

TOI-421 b: A Hot Sub-Neptune with a Haze-Free, Low Mean Molecular Weight Atmosphere

Authors: Brian Davenport, Eliza M. -R. Kempton, Matthew C. Nixon, Jegug Ih, Drake Deming, Guangwei Fu, E. M. May, Jacob L. Bean, Peter Gao, Leslie Rogers, Matej Malik

Abstract: Common features of sub-Neptunes atmospheres observed to date include signatures of aerosols at moderate equilibrium temperatures (~500-800 K), and a prevalence of high mean molecular weight atmospheres, perhaps indicating novel classes of planets such as water worlds. Here we present a 0.83-5 micron JWST transmission spectrum of the sub-Neptune TOI-421 b. This planet is unique among previously obs… ▽ More Common features of sub-Neptunes atmospheres observed to date include signatures of aerosols at moderate equilibrium temperatures (~500-800 K), and a prevalence of high mean molecular weight atmospheres, perhaps indicating novel classes of planets such as water worlds. Here we present a 0.83-5 micron JWST transmission spectrum of the sub-Neptune TOI-421 b. This planet is unique among previously observed counterparts in its high equilibrium temperature ($T_{eq} \approx 920$) and its Sun-like host star. We find marked differences between the atmosphere of TOI-421 b and those of sub-Neptunes previously characterized with JWST, which all orbit M stars. Specifically, water features in the NIRISS/SOSS bandpass indicate a low mean molecular weight atmosphere consistent with solar metallicity, and no appreciable aerosol coverage. Hints of SO$_2$ and CO (but not CO$_2$ or CH$_4$) also exist in our NIRSpec/G395M observations, but not at sufficient signal-to-noise to draw firm conclusions. Our results support a picture in which sub-Neptunes hotter than ~850 K do not form hydrocarbon hazes due to a lack of methane to photolyze. TOI-421 b additionally fits the paradigm of the radius valley for planets orbiting FGK stars being sculpted by mass loss processes, which would leave behind primordial atmospheres overlying rock/iron interiors. Further observations of TOI-421 b and similar hot sub-Neptunes will confirm whether haze-free atmospheres and low mean molecular weights are universal characteristics of such objects. △ Less

Submitted 2 January, 2025; originally announced January 2025.

Comments: Submitted to ApJ Letters, comments welcome

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

Authors: Dana R. Louie, Elijah Mullens, Lili Alderson, Ana Glidden, Nikole K. Lewis, Hannah R. Wakeford, Natasha E. Batalha, Knicole D. Colón, Amélie Gressier, Douglas Long, Michael Radica, Néstor Espinoza, Jayesh Goyal, Ryan J. MacDonald, Erin M. May, Sara Seager, Kevin B. Stevenson, Jeff A. Valenti, Natalie H. Allen, Caleb I. Cañas, Ryan C. Challener, David Grant, Jingcheng Huang, Zifan Lin, Daniel Valentine , et al. (5 additional authors not shown)

Abstract: 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… ▽ More 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 $σ$. 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). △ Less

Submitted 9 January, 2025; v1 submitted 4 December, 2024; originally announced December 2024.

Comments: Accepted for Publication in the Astronomical Journal (AJ) on 19 November 2024; 37 Pages, 17 Figures, 7 Tables. This version adds 2 co-authors, updates affiliations/acknowledgements, and corrects minor typos. Zenodo link to data is at https://zenodo.org/records/14193061

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

Authors: Amélie Gressier, Ryan J. MacDonald, Néstor Espinoza, Hannah R. Wakeford, Nikole K. Lewis, Jayesh Goyal, Dana R. Louie, Michael Radica, Natasha E. Batalha, Douglas Long, Erin M. May, Elijah Mullens, Sara Seager, Kevin B. Stevenson, Jeff A. Valenti, Lili Alderson, Natalie H. Allen, Caleb I. Cañas, Ryan C. Challener, Knicole Colòn, Ana Glidden, David Grant, Jingcheng Huang, Zifan Lin, Daniel Valentine , et al. (4 additional authors not shown)

Abstract: 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 favo… ▽ More 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). △ Less

Submitted 10 October, 2024; originally announced October 2024.

Comments: Accepted for Publication in the Astronomical Journal (AJ) October 4, 2024

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

Authors: Daniel Valentine, Hannah R. Wakeford, Ryan C. Challener, Natasha E. Batalha, Nikole K. Lewis, David Grant, Elijah Mullens, Lili Alderson, Jayesh Goyal, Ryan J. MacDonald, Erin M. May, Sara Seager, Kevin B. Stevenson, Jeff A. Valenti, Natalie H. Allen, Néstor Espinoza, Ana Glidden, Amélie Gressier, Jingcheng Huang, Zifan Lin, Douglas Long, Dana R. Louie, Mark Clampin, Marshall Perrin, Roeland P. van der Marel , et al. (1 additional authors not shown)

Abstract: 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 $μ$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 a… ▽ More 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 $μ$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 $18.7^{+11.1°}_{-3.8}$, 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). △ Less

Submitted 10 October, 2024; originally announced October 2024.

Comments: 28 pages, 8 figures. Published in The Astronomical Journal

Journal ref: The Astronomical Journal, 168:123 (21pp), 2024 September

A Benchmark JWST Near-Infrared Spectrum for the Exoplanet WASP-39b

Authors: A. L. Carter, E. M. May, N. Espinoza, L. Welbanks, E. Ahrer, L. Alderson, R. Brahm, A. D. Feinstein, D. Grant, M. Line, G. Morello, R. O'Steen, M. Radica, Z. Rustamkulov, K. B. Stevenson, J. D. Turner, M. K. Alam, D. R. Anderson, N. M. Batalha, M. P. Battley, D. Bayliss, J. L. Bean, B. Benneke, Z. K. Berta-Thompson, J. Brande , et al. (55 additional authors not shown)

Abstract: Observing exoplanets through transmission spectroscopy supplies detailed information on their atmospheric composition, physics, and chemistry. Prior to JWST, these observations were limited to a narrow wavelength range across the near-ultraviolet to near-infrared, alongside broadband photometry at longer wavelengths. To understand more complex properties of exoplanet atmospheres, improved waveleng… ▽ More Observing exoplanets through transmission spectroscopy supplies detailed information on their atmospheric composition, physics, and chemistry. Prior to JWST, these observations were limited to a narrow wavelength range across the near-ultraviolet to near-infrared, alongside broadband photometry at longer wavelengths. To understand more complex properties of exoplanet atmospheres, improved wavelength coverage and resolution are necessary to robustly quantify the influence of a broader range of absorbing molecular species. Here we present a combined analysis of JWST transmission spectroscopy across four different instrumental modes spanning 0.5-5.2 micron using Early Release Science observations of the Saturn-mass exoplanet WASP-39b. Our uniform analysis constrains the orbital and stellar parameters within sub-percent precision, including matching the precision obtained by the most precise asteroseismology measurements of stellar density to-date, and further confirms the presence of Na, K, H$_2$O, CO, CO$_2$, and SO$_2$ atmospheric absorbers. Through this process, we also improve the agreement between the transmission spectra of all modes, except for the NIRSpec PRISM, which is affected by partial saturation of the detector. This work provides strong evidence that uniform light curve analysis is an important aspect to ensuring reliability when comparing the high-precision transmission spectra provided by JWST. △ Less

Submitted 18 July, 2024; originally announced July 2024.

Comments: 34 pages, 11 figures, 3 tables. Nat Astron (2024)

Inhomogeneous terminators on the exoplanet WASP-39 b

Authors: Néstor Espinoza, Maria E. Steinrueck, James Kirk, Ryan J. MacDonald, Arjun B. Savel, Kenneth Arnold, Eliza M. -R. Kempton, Matthew M. Murphy, Ludmila Carone, Maria Zamyatina, David A. Lewis, Dominic Samra, Sven Kiefer, Emily Rauscher, Duncan Christie, Nathan Mayne, Christiane Helling, Zafar Rustamkulov, Vivien Parmentier, Erin M. May, Aarynn L. Carter, Xi Zhang, Mercedes López-Morales, Natalie Allen, Jasmina Blecic , et al. (18 additional authors not shown)

Abstract: Transmission spectroscopy has been a workhorse technique over the past two decades to constrain the physical and chemical properties of exoplanet atmospheres. One of its classical key assumptions is that the portion of the atmosphere it probes -- the terminator region -- is homogeneous. Several works in the past decade, however, have put this into question for highly irradiated, hot (… ▽ More Transmission spectroscopy has been a workhorse technique over the past two decades to constrain the physical and chemical properties of exoplanet atmospheres. One of its classical key assumptions is that the portion of the atmosphere it probes -- the terminator region -- is homogeneous. Several works in the past decade, however, have put this into question for highly irradiated, hot ($T_{eq}\gtrsim 1000$ K) gas giant exoplanets both empirically and via 3-dimensional modelling. While models predict clear differences between the evening (day-to-night) and morning (night-to-day) terminators, direct morning/evening transmission spectra in a wide wavelength range has not been reported for an exoplanet to date. Under the assumption of precise and accurate orbital parameters on WASP-39 b, here we report the detection of inhomogeneous terminators on the exoplanet WASP-39 b, which allows us to retrieve its morning and evening transmission spectra in the near-infrared ($2-5\ μ$m) using JWST. We observe larger transit depths in the evening which are, on average, $405 \pm 88$ ppm larger than the morning ones, also having qualitatively larger features than the morning spectrum. The spectra are best explained by models in which the evening terminator is hotter than the morning terminator by $177^{+65}_{-57}$ K with both terminators having C/O ratios consistent with solar. General circulation models (GCMs) predict temperature differences broadly consistent with the above value and point towards a cloudy morning terminator and a clearer evening terminator. △ Less

Submitted 14 July, 2024; originally announced July 2024.

Comments: Published in Nature at https://www.nature.com/articles/s41586-024-07768-4. All code to produce plots (with data) can be found at https://github.com/nespinoza/wasp39-terminators

HST SHEL: Enabling Comparative Exoplanetology with HST/STIS

Authors: Natalie H. Allen, David K. Sing, Néstor Espinoza, Richard O'Steen, Nikolay K. Nikolov, Zafar Rustamkulov, Thomas M. Evans-Soma, Lakeisha M. Ramos Rosado, Munazza K. Alam, Mercedes López-Morales, Kevin B. Stevenson, Hannah R. Wakeford, Erin M. May, Rafael Brahm, Marcelo Tala Pinto

Abstract: The Hubble Space Telescope (HST) has been our most prolific tool to study exoplanet atmospheres. As the age of JWST begins, there is a wealth of HST archival data that is useful to strengthen our inferences from JWST. Notably, HST/STIS and its 0.3-1 $μ$m wavelength coverage extends past JWST's 0.6 $μ$m wavelength cutoff and holds an abundance of potential information: alkali (Na, K) and molecular… ▽ More The Hubble Space Telescope (HST) has been our most prolific tool to study exoplanet atmospheres. As the age of JWST begins, there is a wealth of HST archival data that is useful to strengthen our inferences from JWST. Notably, HST/STIS and its 0.3-1 $μ$m wavelength coverage extends past JWST's 0.6 $μ$m wavelength cutoff and holds an abundance of potential information: alkali (Na, K) and molecular (TiO, VO) species opacities, aerosol information, and the presence of stellar contamination. However, time series observations with HST suffer from significant instrumental systematics and can be highly dependent on choices made during the transit fitting process. This makes comparing transmission spectra of planets with different data reduction methodologies challenging, as it is difficult to discern if an observed trend is caused by differences in data reduction or underlying physical processes. Here, we present the Sculpting Hubble's Exoplanet Legacy (SHEL) program, which aims to build a consistent data reduction and light curve analysis methodology and associated database of transmission spectra from archival HST observations. In this paper, we present the SHEL analysis framework for HST/STIS and its low-resolution spectroscopy modes, G430L and G750L. We apply our methodology to four notable hot Jupiters: WASP-39 b, WASP-121 b, WASP-69 b, and WASP-17 b, and use these examples to discuss nuances behind analysis with HST/STIS. Our results for WASP-39 b, WASP-121 b, and WASP-17 b are consistent with past publications, but our analysis of WASP-69 b differs and shows evidence of either a strong scattering slope or stellar contamination. The data reduction pipeline and tutorials are available on Github. △ Less

Submitted 30 May, 2024; originally announced May 2024.

Comments: 36 pages, 25 figures, 4 tables. Accepted for publication in the Astronomical Journal

JWST/NIRCam Transmission Spectroscopy of the Nearby Sub-Earth GJ 341b

Authors: James Kirk, Kevin B. Stevenson, Guangwei Fu, Jacob Lustig-Yaeger, Sarah E. Moran, Sarah Peacock, Munazza K. Alam, Natasha E. Batalha, Katherine A. Bennett, Junellie Gonzalez-Quiles, Mercedes López-Morales, Joshua D. Lothringer, Ryan J. MacDonald, E. M. May, L. C. Mayorga, Zafar Rustamkulov, David K. Sing, Kristin S. Sotzen, Jeff A. Valenti, Hannah R. Wakeford

Abstract: We present a JWST/NIRCam transmission spectrum from $3.9-5.0$ $μ$m of the recently-validated sub-Earth GJ 341b ($\mathrm{R_P} = 0.92$ $\mathrm{R_{\oplus}}$, $\mathrm{T_{eq}} = 540$ K) orbiting a nearby bright M1 star ($\mathrm{d} = 10.4$ pc, $\mathrm{K_{mag}}=5.6$). We use three independent pipelines to reduce the data from the three JWST visits and perform several tests to check for the significa… ▽ More We present a JWST/NIRCam transmission spectrum from $3.9-5.0$ $μ$m of the recently-validated sub-Earth GJ 341b ($\mathrm{R_P} = 0.92$ $\mathrm{R_{\oplus}}$, $\mathrm{T_{eq}} = 540$ K) orbiting a nearby bright M1 star ($\mathrm{d} = 10.4$ pc, $\mathrm{K_{mag}}=5.6$). We use three independent pipelines to reduce the data from the three JWST visits and perform several tests to check for the significance of an atmosphere. Overall, our analysis does not uncover evidence of an atmosphere. Our null hypothesis tests find that none of our pipelines' transmission spectra can rule out a flat line, although there is weak evidence for a Gaussian feature in two spectra from different pipelines (at 2.3 and $2.9σ$). However, the candidate features are seen at different wavelengths (4.3 $μ$m vs 4.7 $μ$m), and our retrieval analysis finds that different gas species can explain these features in the two reductions (CO$_2$ at $3.1σ$ compared to O$_3$ at $2.9σ$), suggesting that they are not real astrophysical signals. Our forward model analysis rules out a low mean molecular weight atmosphere ($< 350\times$ solar metallicity) to at least $3σ$, and disfavors CH$_4$-dominated atmospheres at $1-3σ$, depending on the reduction. Instead, the forward models find our transmission spectra are consistent with no atmosphere, a hazy atmosphere, or an atmosphere containing a species that does not have prominent molecular bands across the NIRCam/F444W bandpass, such as a water-dominated atmosphere. Our results demonstrate the unequivocal need for two or more transit observations analyzed with multiple reduction pipelines, alongside rigorous statistical tests, to determine the robustness of molecular detections for small exoplanet atmospheres. △ Less

Submitted 11 January, 2024; originally announced January 2024.

Comments: 25 pages, 18 figures, 6 tables. Accepted for publication in AJ

A WISPR of the Venus Surface: Analysis of the Venus Nightside Thermal Emission at Optical Wavelengths

Authors: J. Lustig-Yaeger, N. R. Izenberg, M. S. Gilmore, L. C. Mayorga, E. M. May, A. Vourlidas, P. Hess, B. E. Wood, R. A. Howard, N. E. Raouafi, G. N. Arney

Abstract: Parker Solar Probe (PSP) conducted several flybys of Venus while using Venus' gravity for orbital adjustments to enable its daring passes of the Sun. During these flybys, PSP turned to image the nightside of Venus using the Wide-field Imager for Solar PRobe (WISPR) optical telescopes, which unexpectedly observed Venus' surface through its thick and cloudy atmosphere in a theorized, but until-then… ▽ More Parker Solar Probe (PSP) conducted several flybys of Venus while using Venus' gravity for orbital adjustments to enable its daring passes of the Sun. During these flybys, PSP turned to image the nightside of Venus using the Wide-field Imager for Solar PRobe (WISPR) optical telescopes, which unexpectedly observed Venus' surface through its thick and cloudy atmosphere in a theorized, but until-then unobserved near-visible spectral window below 0.8 $μ$m. We use observations taken during PSP's fourth Venus gravity assist flyby to examine the origin of the Venus nightside flux and confirm the presence of this new atmospheric window through which to observe the surface geology of Venus. The WISPR images are well explained by emission from the hot Venus surface escaping through a new atmospheric window in the optical with an overlying emission component from the atmosphere at the limb that is consistent with O$_2$ nightglow. The surface thermal emission correlates strongly with surface elevation (via temperature) and emission angle. Tessera and plains units have distinct WISPR brightness values. Controlling for elevation, Ovda Regio tessera is brighter than Thetis Regio; likewise, the volcanic plains of Sogolon Planitia are brighter than the surrounding regional plains units. WISPR brightness at 0.8 $μ$m is predicted to be positively correlated to FeO content in minerals; thus, the brighter units may have a different starting composition, be less weathered, or have larger particle sizes. △ Less

Submitted 6 November, 2023; originally announced November 2023.

Comments: 12 pages, 10 figures, 2 tables. Published in PSJ

Journal ref: Planet. Sci. J. 4 207 (2023)

Double Trouble: Two Transits of the Super-Earth GJ 1132 b Observed with JWST NIRSpec G395H

Authors: E. M. May, Ryan J. MacDonald, Katherine A. Bennett, Sarah E. Moran, Hannah R. Wakeford, Sarah Peacock, Jacob Lustig-Yaeger, Alicia N. Highland, Kevin B. Stevenson, David K. Sing, L. C. Mayorga, Natasha E. Batalha, James Kirk, Mercedes Lopez-Morales, Jeff A. Valenti, Munazza K. Alam, Lili Alderson, Guangwei Fu, Junellie Gonzalez-Quiles, Joshua D. Lothringer, Zafar Rustamkulov, Kristin S. Sotzen

Abstract: The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transi… ▽ More The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transit observations of the rocky planet GJ 1132 b with JWST NIRSpec G395H, covering 2.8-5.2 $μ$m. Previous HST WFC3 observations of GJ 1132 b were inconclusive, with evidence reported for either an atmosphere or a featureless spectrum based on analyses of the same dataset. Our JWST data exhibit substantial differences between the two visits. One transit is consistent with either a H$_2$O-dominated atmosphere containing ~1% CH$_4$ and trace N$_2$O ($χ^{2}_ν$ = 1.13) or stellar contamination from unocculted starspots ($χ^{2}_ν$ = 1.36). However, the second transit is consistent with a featureless spectrum. Neither visit is consistent with a previous report of HCN. Atmospheric variability is unlikely to explain the scale of the observed differences between the visits. Similarly, our out-of-transit stellar spectra show no evidence of changing stellar inhomogeneity between the two visits - observed 8 days apart, only 6.5% of the stellar rotation rate. We further find no evidence of differing instrumental systematic effects between visits. The most plausible explanation is an unlucky random noise draw leading to two significantly discrepant transmission spectra. Our results highlight the importance of multi-visit repeatability with JWST prior to claiming atmospheric detections for these small, enigmatic planets. △ Less

Submitted 16 October, 2023; originally announced October 2023.

Comments: 22 pages, 10 figures, 2 tables. Accepted for publication in ApJ Letters. Co-First Authors. Bonus materials and spectral data: https://doi.org/10.5281/zenodo.10002089

Journal ref: ApJL (2023): 959, L9

JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b

Authors: David Grant, Nikole K. Lewis, Hannah R. Wakeford, Natasha E. Batalha, Ana Glidden, Jayesh Goyal, Elijah Mullens, Ryan J. MacDonald, Erin M. May, Sara Seager, Kevin B. Stevenson, Jeff A. Valenti, Channon Visscher, Lili Alderson, Natalie H. Allen, Caleb I. Cañas, Knicole Colón, Mark Clampin, Néstor Espinoza, Amélie Gressier, Jingcheng Huang, Zifan Lin, Douglas Long, Dana R. Louie, Maria Peña-Guerrero , et al. (17 additional authors not shown)

Abstract: Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this… ▽ More Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this work, we observe one transit of the hot Jupiter WASP-17b with JWST's MIRI LRS and generate a transmission spectrum from 5-12 $\rmμ$m. These wavelengths allow us to probe absorption due to the vibrational modes of various predicted cloud species. Our transmission spectrum shows additional opacity centered at 8.6 $\rmμ$m, and detailed atmospheric modeling and retrievals identify this feature as SiO$_2$(s) (quartz) clouds. The SiO$_2$(s) clouds model is preferred at 3.5-4.2$σ$ versus a cloud-free model and at 2.6$σ$ versus a generic aerosol prescription. We find the SiO$_2$(s) clouds are comprised of small ${\sim}0.01$ $\rmμ$m particles, which extend to high altitudes in the atmosphere. The atmosphere also shows a depletion of H$_2$O, a finding consistent with the formation of high-temperature aerosols from oxygen-rich species. 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). △ Less

Submitted 7 August, 2024; v1 submitted 12 October, 2023; originally announced October 2023.

Comments: 19 pages, 7 figures, fixed typo in Equation 3

High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations

Authors: Sarah E. Moran, Kevin B. Stevenson, David K. Sing, Ryan J. MacDonald, James Kirk, Jacob Lustig-Yaeger, Sarah Peacock, L. C. Mayorga, Katherine A. Bennett, Mercedes López-Morales, E. M. May, Zafar Rustamkulov, Jeff A. Valenti, Jéa I. Adams Redai, Munazza K. Alam, Natasha E. Batalha, Guangwei Fu, Junellie Gonzalez-Quiles, Alicia N. Highland, Ethan Kruse, Joshua D. Lothringer, Kevin N. Ortiz Ceballos, Kristin S. Sotzen, Hannah R. Wakeford

Abstract: Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to… ▽ More Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 micron JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3x Earth's insolation) super-Earth GJ 486b (1.3 R$_{\oplus}$ and 3.0 M$_{\oplus}$). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 - 3.3 $σ$, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2$σ$) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ($χ^2_ν$ = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere. △ Less

Submitted 4 March, 2026; v1 submitted 1 May, 2023; originally announced May 2023.

Comments: 18 pages, 7 figures, 5 tables. Accepted in ApJ Letters. Co-First Authors. Updated Fig 1 to reflect typo

A JWST transmission spectrum of a nearby Earth-sized exoplanet

Authors: J. Lustig-Yaeger, G. Fu, E. M. May, K. N. Ortiz Ceballos, S. E. Moran, S. Peacock, K. B. Stevenson, M. López-Morales, R. J. MacDonald, L. C. Mayorga, D. K. Sing, K. S. Sotzen, J. A. Valenti, J. Adams, M. K. Alam, N. E. Batalha, K. A. Bennett, J. Gonzalez-Quiles, J. Kirk, E. Kruse, J. D. Lothringer, Z. Rustamkulov, H. R. Wakeford

Abstract: The critical first step in the search for life on exoplanets over the next decade is to determine whether rocky planets transiting small M-dwarf stars possess atmospheres and, if so, what processes sculpt them over time. Because of its broad wavelength coverage and improved resolution compared to previous methods, spectroscopy with JWST offers a new capability to detect and characterize the atmosp… ▽ More The critical first step in the search for life on exoplanets over the next decade is to determine whether rocky planets transiting small M-dwarf stars possess atmospheres and, if so, what processes sculpt them over time. Because of its broad wavelength coverage and improved resolution compared to previous methods, spectroscopy with JWST offers a new capability to detect and characterize the atmospheres of Earth-sized, M-dwarf planets. Here we use JWST to independently validate the discovery of LHS 475b, a warm (586 K), 0.99 Earth-radius exoplanet, interior to the habitable zone, and report a precise 2.9-5.3 um transmission spectrum. With two transit observations, we rule out primordial hydrogen-dominated and cloudless pure methane atmospheres. Thus far, the featureless transmission spectrum remains consistent with a planet that has a high-altitude cloud deck (similar to Venus), a tenuous atmosphere (similar to Mars), or no appreciable atmosphere at all (akin to Mercury). There are no signs of stellar contamination due to spots or faculae. Our observations demonstrate that JWST has the requisite sensitivity to constrain the secondary atmospheres of terrestrial exoplanets with absorption features <50 ppm, and that our current atmospheric constraints speak to the nature of the planet itself, rather than instrumental limits. △ Less

Submitted 10 January, 2023; originally announced January 2023.

Comments: A co-first author paper Lustig-Yaeger and Fu et al., Nature Astronomy (2023), Comments welcome

GCM Constraints on the Detectability of the CO$_2$-CH$_4$ Biosignature Pair on TRAPPIST-1e with JWST

Authors: Yoav Rotman, Thaddeus D. Komacek, Geronimo L. Villanueva, Thomas J. Fauchez, Erin M. May

Abstract: Terrestrial exoplanets such as TRAPPIST-1e will be observed in a new capacity with JWST/NIRSpec, which is expected to be able to detect CO$_2$, CH$_4$, and O$_2$ signals, if present, with multiple co-added transit observations. The CO$_2$-CH$_4$ pair in particular is theorized to be a potential biosignature when inferred to be in chemical disequilibrium. Here, we simulate TRAPPIST-1e's atmosphere… ▽ More Terrestrial exoplanets such as TRAPPIST-1e will be observed in a new capacity with JWST/NIRSpec, which is expected to be able to detect CO$_2$, CH$_4$, and O$_2$ signals, if present, with multiple co-added transit observations. The CO$_2$-CH$_4$ pair in particular is theorized to be a potential biosignature when inferred to be in chemical disequilibrium. Here, we simulate TRAPPIST-1e's atmosphere using the ExoCAM General Circulation Model (GCM), assuming an optimistic haze-free, tidally locked planet with an aquaplanet surface, with varying atmospheric compositions from $10^{-4}$ bar to 1 bar of partial CO$_2$ pressure with 1 bar of background N$_2$. We investigate cases both with and without a modern Earth-like CH$_4$ mixing ratio to examine the effect of CO$_2$ and CH$_4$ on the transmission spectrum and climate state of the planet. We demonstrate that in the optimistic haze-free cloudy case, H$_2$O, CO$_2$, and CH$_4$ could all be detectable in less than 50 transits within an atmosphere of 1 bar N$_2$ and 10 mbar CO$_2$ during JWST's lifespan with NIRSpec as long as the noise floor is $\lesssim$ 10 ppm. We find that in these optimistic cases, JWST may be able to detect potential biosignature pairs such as CO$_2$-CH$_4$ in TRAPPIST-1e's atmosphere across a variety of atmospheric CO$_2$ content, and that temporal climate variability does not significantly affect spectral feature variability for NIRSpec PRISM. △ Less

Submitted 9 December, 2022; originally announced December 2022.

Comments: 11 pages, 4 figures, 1 table, accepted for publication in ApJL

The effect of interior heat flux on the atmospheric circulation of hot and ultra-hot Jupiters

Authors: Thaddeus D. Komacek, Peter Gao, Daniel P. Thorngren, Erin M. May, Xianyu Tan

Abstract: Many hot and ultra-hot Jupiters have inflated radii, implying that their interiors retain significant entropy from formation. These hot interiors lead to an enhanced internal heat flux that impinges upon the atmosphere from below. In this work, we study the effect of this hot interior on the atmospheric circulation and thermal structure of hot and ultra-hot Jupiters. To do so, we incorporate the p… ▽ More Many hot and ultra-hot Jupiters have inflated radii, implying that their interiors retain significant entropy from formation. These hot interiors lead to an enhanced internal heat flux that impinges upon the atmosphere from below. In this work, we study the effect of this hot interior on the atmospheric circulation and thermal structure of hot and ultra-hot Jupiters. To do so, we incorporate the population-level predictions from evolutionary models of hot and ultra-hot Jupiters as input for a suite of General Circulation Models (GCMs) of their atmospheric circulation with varying semi-major axis and surface gravity. We conduct simulations with and without a hot interior, and find that there are significant local differences in temperature of up to hundreds of Kelvin and in wind speeds of hundreds of m s$^{-1}$ or more across the observable atmosphere. These differences persist throughout the parameter regime studied, and are dependent on surface gravity through the impact on photosphere pressure. These results imply that the internal evolution and atmospheric thermal structure and dynamics of hot and ultra-hot Jupiters are coupled. As a result, a joint approach including both evolutionary models and GCMs may be required to make robust predictions for the atmospheric circulation of hot and ultra-hot Jupiters. △ Less

Submitted 7 December, 2022; originally announced December 2022.

Comments: Accepted at ApJL, 17 pages, 8 figures

Journal ref: The Astrophysical Journal Letters, 941:L40 (12pp), 2022 December 20

Early Release Science of the exoplanet WASP-39b with JWST NIRISS

Authors: Adina D. Feinstein, Michael Radica, Luis Welbanks, Catriona Anne Murray, Kazumasa Ohno, Louis-Philippe Coulombe, Néstor Espinoza, Jacob L. Bean, Johanna K. Teske, Björn Benneke, Michael R. Line, Zafar Rustamkulov, Arianna Saba, Angelos Tsiaras, Joanna K. Barstow, Jonathan J. Fortney, Peter Gao, Heather A. Knutson, Ryan J. MacDonald, Thomas Mikal-Evans, Benjamin V. Rackham, Jake Taylor, Vivien Parmentier, Natalie M. Batalha, Zachory K. Berta-Thompson , et al. (64 additional authors not shown)

Abstract: Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has… ▽ More Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans $0.6 - 2.8 μ$m in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of $\sim 10 - 30 \times$ the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator. △ Less

Submitted 18 November, 2022; originally announced November 2022.

Comments: 48 pages, 12 figures, 2 tables. Under review at Nature

Early Release Science of the exoplanet WASP-39b with JWST NIRCam

Authors: Eva-Maria Ahrer, Kevin B. Stevenson, Megan Mansfield, Sarah E. Moran, Jonathan Brande, Giuseppe Morello, Catriona A. Murray, Nikolay K. Nikolov, Dominique J. M. Petit dit de la Roche, Everett Schlawin, Peter J. Wheatley, Sebastian Zieba, Natasha E. Batalha, Mario Damiano, Jayesh M Goyal, Monika Lendl, Joshua D. Lothringer, Sagnick Mukherjee, Kazumasa Ohno, Natalie M. Batalha, Matthew P. Battley, Jacob L. Bean, Thomas G. Beatty, Björn Benneke, Zachory K. Berta-Thompson , et al. (74 additional authors not shown)

Abstract: Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength covera… ▽ More Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution, and high precision that, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0 - 4.0 $μ$m, exhibit minimal systematics, and reveal well-defined molecular absorption features in the planet's spectrum. Specifically, we detect gaseous H$_2$O in the atmosphere and place an upper limit on the abundance of CH$_4$. The otherwise prominent CO$_2$ feature at 2.8 $μ$m is largely masked by H$_2$O. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1-100$\times$ solar (i.e., an enrichment of elements heavier than helium relative to the Sun) and a sub-stellar carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere. △ Less

Submitted 18 November, 2022; originally announced November 2022.

Comments: 35 pages, 13 figures, 3 tables, Nature, accepted

Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H

Authors: Lili Alderson, Hannah R. Wakeford, Munazza K. Alam, Natasha E. Batalha, Joshua D. Lothringer, Jea Adams Redai, Saugata Barat, Jonathan Brande, Mario Damiano, Tansu Daylan, Néstor Espinoza, Laura Flagg, Jayesh M. Goyal, David Grant, Renyu Hu, Julie Inglis, Elspeth K. H. Lee, Thomas Mikal-Evans, Lakeisha Ramos-Rosado, Pierre-Alexis Roy, Nicole L. Wallack, Natalie M. Batalha, Jacob L. Bean, Björn Benneke, Zachory K. Berta-Thompson , et al. (67 additional authors not shown)

Abstract: Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the m… ▽ More Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the medium-resolution (R$\sim$600) transmission spectrum of an exoplanet atmosphere between 3-5 $μ$m covering multiple absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO$_2$ (28.5$σ$) and H$_2$O (21.5$σ$), and identify SO$_2$ as the source of absorption at 4.1 $μ$m (4.8$σ$). Best-fit atmospheric models range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO$_2$, underscore the importance of characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec G395H as an excellent mode for time series observations over this critical wavelength range. △ Less

Submitted 18 November, 2022; originally announced November 2022.

Comments: 44 pages, 11 figures, 3 tables. Resubmitted after revision to Nature

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

Authors: Z. Rustamkulov, D. K. Sing, S. Mukherjee, E. M. May, J. Kirk, E. Schlawin, M. R. Line, C. Piaulet, A. L. Carter, N. E. Batalha, J. M. Goyal, M. López-Morales, J. D. Lothringer, R. J. MacDonald, S. E. Moran, K. B. Stevenson, H. R. Wakeford, N. Espinoza, J. L. Bean, N. M. Batalha, B. Benneke, Z. K. Berta-Thompson, I. J. M. Crossfield, P. Gao, L. Kreidberg , et al. (69 additional authors not shown)

Abstract: Transmission spectroscopy of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species… ▽ More Transmission spectroscopy of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species$-$in particular the primary carbon-bearing molecules. Here we report a broad-wavelength 0.5-5.5 $μ$m atmospheric transmission spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting Exoplanet Community Early Release Science Team program. We robustly detect multiple chemical species at high significance, including Na (19$σ$), H$_2$O (33$σ$), CO$_2$ (28$σ$), and CO (7$σ$). The non-detection of CH$_4$, combined with a strong CO$_2$ feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4$μ$m is best explained by SO$_2$ (2.7$σ$), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes. △ Less

Submitted 18 November, 2022; originally announced November 2022.

Comments: 41 pages, 4 main figures, 10 extended data figures, 4 tables. Under review in Nature

Identification of carbon dioxide in an exoplanet atmosphere

Authors: The JWST Transiting Exoplanet Community Early Release Science Team, Eva-Maria Ahrer, Lili Alderson, Natalie M. Batalha, Natasha E. Batalha, Jacob L. Bean, Thomas G. Beatty, Taylor J. Bell, Björn Benneke, Zachory K. Berta-Thompson, Aarynn L. Carter, Ian J. M. Crossfield, Néstor Espinoza, Adina D. Feinstein, Jonathan J. Fortney, Neale P. Gibson, Jayesh M. Goyal, Eliza M. -R. Kempton, James Kirk, Laura Kreidberg, Mercedes López-Morales, Michael R. Line, Joshua D. Lothringer, Sarah E. Moran, Sagnick Mukherjee , et al. (107 additional authors not shown)

Abstract: Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called "metallicity"), and thus formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres… ▽ More Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called "metallicity"), and thus formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2 but have not yielded definitive detections due to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science Program (ERS). The data used in this study span 3.0 to 5.5 μm in wavelength and show a prominent CO2 absorption feature at 4.3 μm (26σ significance). The overall spectrum is well matched by one-dimensional, 10x solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide, and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 μm that is not reproduced by these models. △ Less

Submitted 24 August, 2022; originally announced August 2022.

Comments: 27 pages, 6 figures, Accepted for publication in Nature, data and models available at https://doi.10.5281/zenodo.6959427

Eureka!: An End-to-End Pipeline for JWST Time-Series Observations

Authors: Taylor J. Bell, Eva-Maria Ahrer, Jonathan Brande, Aarynn L. Carter, Adina D. Feinstein, Giannina Guzman Caloca, Megan Mansfield, Sebastian Zieba, Caroline Piaulet, Björn Benneke, Joseph Filippazzo, Erin M. May, Pierre-Alexis Roy, Laura Kreidberg, Kevin B. Stevenson

Abstract: $\texttt{Eureka!}… ▽ More $\texttt{Eureka!}$ is a data reduction and analysis pipeline for exoplanet time-series observations, with a particular focus on JWST data. Over the next 1-2 decades, JWST will pursue four main science themes: Early Universe, Galaxies Over Time, Star Lifecycle, and Other Worlds. Our focus is on providing the astronomy community with an open source tool for the reduction and analysis of time-series observations of exoplanets in pursuit of the fourth of these themes, Other Worlds. The goal of $\texttt{Eureka!}$ is to provide an end-to-end pipeline that starts with uncalibrated FITS files and ultimately yields precise exoplanet spectra. The pipeline has a modular structure with six stages, and each stage uses a "Eureka! Control File" (ECF) to allow for easy control of the pipeline's behavior. Stage 5 also uses a "Eureka! Parameter File" (EPF) to control the fitted parameters. We provide template ECFs for the MIRI, NIRCam, NIRISS, and NIRSpec instruments on JWST and the WFC3 instrument on the Hubble Space Telescope (HST). These templates give users a good starting point for their analyses, but $\texttt{Eureka!}$ is not intended to be used as a black box tool, and users should expect to fine-tune some settings for each observation in order to achieve optimal results. At each stage, the pipeline creates intermediate figures and outputs that allow users to compare $\texttt{Eureka!}$'s performance using different parameter settings or to compare $\texttt{Eureka!}$ with an independent pipeline. The ECF used to run each stage is also copied into the output folder from each stage to enhance reproducibility. Finally, while $\texttt{Eureka!}$ has been optimized for exoplanet observations (especially the latter stages of the code), much of the core functionality could also be repurposed for JWST time-series observations in other research domains thanks to $\texttt{Eureka!}$'s modularity. △ Less

Submitted 5 January, 2023; v1 submitted 7 July, 2022; originally announced July 2022.

Comments: 6 pages, 1 figure, published in JOSS

Journal ref: Journal of Open Source Software, 7(79), 4503

A Comprehensive Analysis of WASP-17b's Transmission Spectrum from Space-Based Observations

Authors: L. Alderson, H. R. Wakeford, R. J. MacDonald, N. K. Lewis, E. M. May, D. Grant, D. K. Sing, K. B. Stevenson, J. Fowler, J. Goyal, N. E. Batalha, T. Kataria

Abstract: Due to its 1770 K equilibrium temperature, WASP-17b, a 1.99 $R_\mathrm{Jup}$, 0.486 $M_\mathrm{Jup}$ exoplanet, sits at the critical juncture between hot and ultra-hot Jupiters. We present its 0.3-5 $μm$ transmission spectrum, with newly obtained with Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) measurements, and, taking advantage of improved analysis techniques, reanalysed HST Space Te… ▽ More Due to its 1770 K equilibrium temperature, WASP-17b, a 1.99 $R_\mathrm{Jup}$, 0.486 $M_\mathrm{Jup}$ exoplanet, sits at the critical juncture between hot and ultra-hot Jupiters. We present its 0.3-5 $μm$ transmission spectrum, with newly obtained with Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) measurements, and, taking advantage of improved analysis techniques, reanalysed HST Space Telescope Imaging Spectrograph (STIS) and Spitzer Space Telescope Infrared Array Camera (IRAC) observations. We achieve a median precision of 132 ppm, with a mean of 272 ppm across the whole spectrum. We additionally make use of Transiting Exoplanet Survey Satellite (TESS) and ground-based transit observations to refine the orbital period of WASP-17b. To interpret the observed atmosphere, we make use of free and equilibrium chemistry retrievals using the POSEIDON and ATMO retrieval codes respectively. We detect absorption due to H$_2$O at $>7 σ$, and find evidence of absorption due to CO$_2$ at $>3 σ$. We see no evidence of previously detected Na and K absorption. Across an extensive suite of retrieval configurations, we find the data favours a bimodal solution with high or low metallicity modes as a result of poor constraints in the optical, and demonstrate the importance of using multiple statistics for model selection. Future James Webb Space Telescope (JWST) GTO observations, combined with the presented transmission spectrum, will enable precise constraints on WASP-17b's atmosphere. △ Less

Submitted 4 March, 2022; originally announced March 2022.

Comments: 25 pages, 13 figures, 10 tables. Accepted for publication in MNRAS

Hierarchical Bayesian Atmospheric Retrieval Modeling for Population Studies of Exoplanet Atmospheres: A Case Study on the Habitable Zone

Authors: Jacob Lustig-Yaeger, Kristin S. Sotzen, Kevin B. Stevenson, Rodrigo Luger, Erin M. May, L. C. Mayorga, Kathleen Mandt, Noam R. Izenberg

Abstract: With the growing number of spectroscopic observations and observational platforms capable of exoplanet atmospheric characterization, there is a growing need for analysis techniques that can distill information about a large population of exoplanets into a coherent picture of atmospheric trends expressed within the statistical sample. In this work, we develop a Hierarchical Bayesian Atmospheric Ret… ▽ More With the growing number of spectroscopic observations and observational platforms capable of exoplanet atmospheric characterization, there is a growing need for analysis techniques that can distill information about a large population of exoplanets into a coherent picture of atmospheric trends expressed within the statistical sample. In this work, we develop a Hierarchical Bayesian Atmospheric Retrieval (HBAR) model to infer population-level trends in exoplanet atmospheric characteristics. We demonstrate HBAR on the case of inferring a trend in atmospheric CO2 with incident stellar flux, predicted by the presence of a functioning carbonate-silicate weathering negative feedback cycle, an assumption upon which all calculations of the habitable zone (HZ) rest. Using simulated transmission spectra and JWST-quality observations of rocky planets with H2O, CO2, and N2 bearing atmospheres, we find that the predicted trend in CO2 causes subtle differences in the spectra of order 10 ppm in the 1-5 um range, underscoring the challenge inherent to testing this hypothesis. In the limit of highly precise data (100 stacked transits per planet), we show that our HBAR model is capable of inferring the population-level parameters that characterize the trend in CO2, and we demonstrate that the null hypothesis and other simpler trends can be rejected at high confidence. Although we find that this specific empirical test of the HZ may be prohibitively challenging in the JWST era, the HBAR framework developed in this work may find a more immediate usage for the analysis of gas giant spectra observed with JWST, Ariel, and other upcoming missions. △ Less

Submitted 1 February, 2022; originally announced February 2022.

Comments: 15 pages, 5 figures, accepted for publication in AJ

Retrieving Exoplanet Atmospheres using Planetary Infrared Excess: Prospects for the Nightside of WASP-43 b and other Hot Jupiters

Authors: Jacob Lustig-Yaeger, Kevin B. Stevenson, L. C. Mayorga, Kristin S. Sotzen, Erin M. May, Noam R. Izenberg, Kathleen Mandt

Abstract: To increase the sample size of future atmospheric characterization efforts, we build on the planetary infrared excess (PIE) technique that has been proposed as a means to detect and characterize the thermal spectra of transiting and non-transiting exoplanets using sufficiently broad wavelength coverage to uniquely constrain the stellar and planetary spectral components from spatially unresolved ob… ▽ More To increase the sample size of future atmospheric characterization efforts, we build on the planetary infrared excess (PIE) technique that has been proposed as a means to detect and characterize the thermal spectra of transiting and non-transiting exoplanets using sufficiently broad wavelength coverage to uniquely constrain the stellar and planetary spectral components from spatially unresolved observations. We performed simultaneous retrievals of stellar and planetary spectra for the archetypal planet WASP-43b in its original configuration and a non-transiting configuration to determine the efficacy of the PIE technique for characterizing the planet's nightside atmospheric thermal structure and composition using typical out-of-transit JWST observations. We found that using PIE with JWST should enable the stellar and planetary spectra to be disentangled with no degeneracies seen between the two flux sources, thus allowing robust constraints on the planet's nightside thermal structure and water abundance to be retrieved. The broad wavelength coverage achieved by combining spectra from NIRISS, NIRSpec, and MIRI enables PIE retrievals that are within 10% of the precision attained using traditional secondary eclipse measurements, although mid-IR observations with MIRI alone may face up to 3.5 times lower precision on the planet's irradiation temperature. For non-transiting planets with unconstrained radius priors, we were able to identify and break the degeneracy between planet radius and irradiation temperature using data that resolved the peak of both the stellar and planetary spectra, thus potentially increasing the number of planets amenable to atmospheric characterization with JWST and other future mission concepts. △ Less

Submitted 5 October, 2021; originally announced October 2021.

Comments: 13 pages, 5 figures, accepted to ApJ Letters

On the Utility of Transmission Color Analysis I: Differentiating Super-Earths and Sub-Neptunes

Authors: Kristin S. Sotzen, Kevin B. Stevenson, Erin M. May, Natasha E. Batalha, Noam R. Izenberg, Sarah M. Horst, Calley L. Tinsman, Carey M. Lisse, Nikole K. Lewis, Jayesh M. Goyal, Joseph J. Linden, Kathleen E. Mandt

Abstract: The majority of exoplanets found to date have been discovered via the transit method, and transmission spectroscopy represents the primary method of studying these distant worlds. Currently, in-depth atmospheric characterization of transiting exoplanets entails the use of spectrographs on large telescopes, requiring significant observing time to study each planet. Previous studies have demonstrate… ▽ More The majority of exoplanets found to date have been discovered via the transit method, and transmission spectroscopy represents the primary method of studying these distant worlds. Currently, in-depth atmospheric characterization of transiting exoplanets entails the use of spectrographs on large telescopes, requiring significant observing time to study each planet. Previous studies have demonstrated trends for solar system worlds using color-color photometry of reflectance spectra, as well as trends within transmission spectra for hot Jupiters. Building on these concepts, we have investigated the use of transmission color photometric analysis for efficient, coarse categorization of exoplanets and for assessing the nature of these worlds, with a focus on resolving the bulk composition degeneracy to aid in discriminating super-Earths and sub-Neptunes. We present our methodology and first results, including spectrum models, model comparison frameworks, and wave band selection criteria. We present our results for different transmission "color" metrics, filter selection methods, and numbers of filters. Assuming noise-free spectra of isothermal atmospheres in chemical equilibrium, with our pipeline, we are able to constrain atmospheric mean molecular weight in order to distinguish between super-Earth and sub-Neptune atmospheres with >90$\%$ overall accuracy using as few as two specific low-resolution filter combinations. We also found that increasing the number of filters does not substantially impact this performance. This method could allow for broad characterization of large numbers of planets much more efficiently than current methods permit, enabling population and system-level studies. Additionally, data collected via this method could inform follow-up observing time by large telescopes for more detailed studies of worlds of interest. △ Less

Submitted 6 September, 2021; originally announced September 2021.

No umbrella needed: Confronting the hypothesis of iron rain on WASP-76b with post-processed general circulation models

Authors: Arjun B. Savel, Eliza M. -R. Kempton, Matej Malik, Thaddeus D. Komacek, Jacob L. Bean, Erin M. May, Kevin B. Stevenson, Megan Mansfield, Emily Rauscher

Abstract: High-resolution spectra are unique indicators of three-dimensional processes in exoplanetary atmospheres. For instance, in 2020, Ehrenreich et al. reported transmission spectra from the ESPRESSO spectrograph yielding an anomalously large Doppler blueshift from the ultra-hot Jupiter WASP-76b. Interpretations of these observations invoke toy model depictions of gas-phase iron condensation in lower-t… ▽ More High-resolution spectra are unique indicators of three-dimensional processes in exoplanetary atmospheres. For instance, in 2020, Ehrenreich et al. reported transmission spectra from the ESPRESSO spectrograph yielding an anomalously large Doppler blueshift from the ultra-hot Jupiter WASP-76b. Interpretations of these observations invoke toy model depictions of gas-phase iron condensation in lower-temperature regions of the planet's atmosphere. In this work, we forward model the atmosphere of WASP-76b with double-gray general circulation models (GCMs) and ray-striking radiative transfer to diagnose the planet's high-resolution transmission spectrum. We confirm that a physical mechanism driving strong east-west asymmetries across the terminator must exist to reproduce large Doppler blueshifts in WASP-76b's transmission spectrum. We identify low atmospheric drag and a deep radiative-convective boundary as necessary components of our GCM to produce this asymmetry (the latter is consistent with existing Spitzer phase curves). However, we cannot reproduce either the magnitude or the time-dependence of the WASP-76b Doppler signature with gas-phase iron condensation alone. Instead, we find that high-altitude, optically thick clouds composed of $\rm Al_2O_3$, Fe, or $\rm Mg_2SiO_4$ provide reasonable fits to the Ehrenreich et al. observations -- with marginal contributions from condensation. This fit is further improved by allowing a small orbital eccentricity ($e \approx 0.017$), consistent with prior WASP-76b orbital constraints. We additionally validate our forward-modeled spectra by reproducing lines of nearly all species detected in WASP-76b by Tabernero et al. 2021. Our procedure's success in diagnosing phase-resolved Doppler shifts demonstrates the benefits of physical, self-consistent, three-dimensional simulations in modeling high-resolution spectra of exoplanet atmospheres. △ Less

Submitted 16 December, 2021; v1 submitted 31 August, 2021; originally announced September 2021.

Comments: 28 pages, 14 figures. Accepted to ApJ

Transmission Spectroscopy of the Earth-Sun System to Inform the Search for Extrasolar Life

Authors: L. C. Mayorga, J. Lustig-Yaeger, E. M. May, Kristin S. Sotzen, Junellie Gonzalez-Quiles, Brian M. Kilpatrick, Emily C. Martin, Kathleen Mandt, K. B. Stevenson, N. R. Izenberg

Abstract: Upcoming NASA astrophysics missions such as the James Webb Space Telescope will search for signs of life on planets transiting nearby stars. Doing so will require co-adding dozens of transmission spectra to build up sufficient signal to noise while simultaneously accounting for challenging systematic effects such as surface/weather variability, atmospheric refraction, and stellar activity. To dete… ▽ More Upcoming NASA astrophysics missions such as the James Webb Space Telescope will search for signs of life on planets transiting nearby stars. Doing so will require co-adding dozens of transmission spectra to build up sufficient signal to noise while simultaneously accounting for challenging systematic effects such as surface/weather variability, atmospheric refraction, and stellar activity. To determine the magnitude and impacts of both stellar and planet variability on measured transmission spectra, we must assess the feasibility of stacking multiple transmission spectra of exo-Earths around their host stars. Using our own solar system, we can determine if current methodologies are sufficient to detect signs of life in Earth's atmosphere and measure the abundance of habitability indicators, such as H2O and CO2, and biosignature pairs, such as O2 and CH4. We assess the impact on transmission spectra of Earth transiting across the Sun from solar and planetary variability and identify remaining unknowns for understanding exoplanet transmission spectra. We conclude that a satellite observing Earth transits across the Sun from beyond L2 is necessary to address these long-standing concerns about the reliability of co-adding planet spectra at UV, optical, and infrared wavelengths from multiple transits in the face of relatively large astrophysical systematics. △ Less

Submitted 28 July, 2021; originally announced July 2021.

Comments: 13 pages, 8 figures, accepted to the Planetary Science Journal

Spitzer phase curve observations and circulation models of the inflated ultra-hot Jupiter WASP-76b

Authors: Erin M. May, Thaddeus D. Komacek, Kevin B. Stevenson, Eliza M. -R. Kempton, Jacob L. Bean, Matej Malik, Jegug Ih, Megan Mansfield, Arjun B. Savel, Drake Deming, Jean-Michel Desert, Y. Katherina Feng, Jonathan J. Fortney, Tiffany Kataria, Nikole Lewis, Caroline Morley, Emily Rauscher, Adam Showman

Abstract: The large radii of many hot Jupiters can only be matched by models that have hot interior adiabats, and recent theoretical work has shown that the interior evolution of hot Jupiters has a significant impact on their atmospheric structure. Due to its inflated radius, low gravity, and ultra-hot equilibrium temperature, WASP-76b is an ideal case study for the impact of internal evolution on observabl… ▽ More The large radii of many hot Jupiters can only be matched by models that have hot interior adiabats, and recent theoretical work has shown that the interior evolution of hot Jupiters has a significant impact on their atmospheric structure. Due to its inflated radius, low gravity, and ultra-hot equilibrium temperature, WASP-76b is an ideal case study for the impact of internal evolution on observable properties. Hot interiors should most strongly affect the non-irradiated side of the planet, and thus full phase curve observations are critical to ascertain the effect of the interior on the atmospheres of hot Jupiters. In this work, we present the first Spitzer phase curve observations of WASP-76b. We find that WASP-76b has an ultra-hot day side and relatively cold nightside with brightness temperatures of $2471 \pm 27~\mathrm{K}$/$1518 \pm 61~\mathrm{K}$ at $3.6~\micron$ and $2699 \pm 32~\mathrm{K}$/$1259 \pm 44~\mathrm{K}$ at $4.5~\micron$, respectively. These results provide evidence for a dayside thermal inversion. Both channels exhibit small phase offsets of $0.68 \pm 0.48^{\circ}$ at $3.6~\micron$ and $0.67 \pm 0.2^{\circ}$ at $4.5~μ\mathrm{m}$. We compare our observations to a suite of general circulation models that consider two end-members of interior temperature along with a broad range of frictional drag strengths. Strong frictional drag is necessary to match the small phase offsets and cold nightside temperatures observed. From our suite of cloud-free GCMs, we find that only cases with a cold interior can reproduce the cold nightsides and large phase curve amplitude at $4.5~\micron$, hinting that the hot interior adiabat of WASP-76b does not significantly impact its atmospheric dynamics or that clouds blanket its nightside. △ Less

Submitted 18 August, 2021; v1 submitted 7 July, 2021; originally announced July 2021.

Comments: 24 pages, 10 Figures, 5 Tables. Accepted to AJ. Co-First Authors

Variable Irradiation on 1D Cloudless Eccentric Exoplanet Atmospheres

Authors: L. C. Mayorga, Tyler D. Robinson, Mark S. Marley, E. M. May, Kevin B. Stevenson

Abstract: Exoplanets on eccentric orbits experience an incident stellar flux that can be markedly larger at periastron versus apoastron. This variation in instellation can lead to dramatic changes in atmospheric structure in regions of the atmosphere where the radiative and advective heating/cooling timescales are shorter than the orbital timescale. To explore this phenomenon, we develop a sophisticated one… ▽ More Exoplanets on eccentric orbits experience an incident stellar flux that can be markedly larger at periastron versus apoastron. This variation in instellation can lead to dramatic changes in atmospheric structure in regions of the atmosphere where the radiative and advective heating/cooling timescales are shorter than the orbital timescale. To explore this phenomenon, we develop a sophisticated one-dimensional (vertical) time-stepping atmospheric structure code, EGP+, capable of simulating the dynamic response of atmospheric thermal and chemical structure to time-dependent perturbations. Critically, EGP+ can efficiently simulate multiple orbits of a planet, thereby providing new opportunities for exoplanet modeling without the need for more computationally-expensive models. We make the simplifying assumption of cloud-free atmospheres, and apply our model to HAT-P-2b, HD~17156b, and HD~80606b, which are known to be on higher-eccentricity orbits. We find that for those planets which have Spitzer observations, our planet-to-star ratio predictions are roughly consistent with observations. However, we are unable to reproduce the observed peak offsets from periastron passage. Finally, we discuss promising pathways forward for adding new model complexity that would enable more detailed studies of clear and cloudy eccentric planets as well as worlds orbiting active host stars. △ Less

Submitted 17 May, 2021; originally announced May 2021.

Comments: 13 pages, 6 figures, 2 tables, accepted to ApJ

Detection of Rotational Variability in Floofy Objects at Optical Wavelengths

Authors: L. C. Mayorga, E. M. May, J. Lustig-Yaeger, S. E Moran

Abstract: Phase resolved observations of planetary bodies allow us to understand the longitudinal and latitudinal variations that make each one unique. Rotational variations have been detected in several types of astronomical bodies beyond those of planetary mass, including asteroids, brown dwarfs, and stars. Unexpected rotational variations, such as those presented in this work, reminds us that the univers… ▽ More Phase resolved observations of planetary bodies allow us to understand the longitudinal and latitudinal variations that make each one unique. Rotational variations have been detected in several types of astronomical bodies beyond those of planetary mass, including asteroids, brown dwarfs, and stars. Unexpected rotational variations, such as those presented in this work, reminds us that the universe can be complicated, with more mysteries to uncover. In this work we present evidence for a new class of astronomical objects we identify as "floofy" with observational distinctions between several sub-types of these poorly understood objects. Using optical observations contributed by the community, we have identified rotational variation in several of these floofy objects, which suggests that they may have strong differences between their hemispheres, likely caused by differing reflectivity off their surfaces. Additional sub-types show no rotational variability suggesting a uniform distribution of reflective elements on the floofy object. While the work here is a promising step towards the categorization of floofy objects, further observations with more strictly defined limits on background light, illumination angles, and companion objects are necessary to develop a better understanding of the many remaining mysteries of these astronomical objects. △ Less

Submitted 30 March, 2021; originally announced March 2021.

Comments: 11 pages, 7 figures, 1 table, to be submitted to the Catstrophysical Journal

Water Ice Cloud Variability & Multi-Epoch Transmission Spectra of TRAPPIST-1e

Authors: E. M. May, J. Taylor, T. D. Komacek, M. R. Line, V. Parmentier

Abstract: The precise characterization of terrestrial atmospheres with the James Webb Space Telescope (JWST) is one of the utmost goals of exoplanet astronomy in the next decade. With JWST's impending launch, it is crucial we are well prepared to understand the subtleties of terrestrial atmospheres - particularly ones we may have not needed to consider before due to instrumentation limitations. In this work… ▽ More The precise characterization of terrestrial atmospheres with the James Webb Space Telescope (JWST) is one of the utmost goals of exoplanet astronomy in the next decade. With JWST's impending launch, it is crucial we are well prepared to understand the subtleties of terrestrial atmospheres - particularly ones we may have not needed to consider before due to instrumentation limitations. In this work we show that patchy ice cloud variability is present in the upper atmospheres of M-dwarf terrestrial planets, particularly along the limbs. Here we test whether these variable clouds will introduce unexpected biases in the multi-epoch observations necessary to constrain atmospheric abundances. Using 3D ExoCAM general circulation models (GCMs) of TRAPPIST-1e, we simulate five different climates with varying pCO$_2$ to explore the strength of this variability. These models are post-processed using NASA Goddard's Planetary Spectrum Generator (PSG) and PandExo to generate simulated observations with JWST's NIRSpec PRISM mode at 365 different temporal outputs from each climate. Assuming the need for 10 transits of TRAPPIST-1e to detect molecular features at great confidence, we then use CHIMERA to retrieve on several randomly selected weighted averages of our simulated observations to explore the effect of multi-epoch observations with variable cloud cover along the limb on retrieved abundances. We find that the variable spectra do not affect retrieved abundances at detectable levels for our sample of TRAPPIST-1e models. △ Less

Submitted 16 March, 2021; originally announced March 2021.

Comments: 9 pages, 5 figures. Accepted to ApJL

Introducing a New Spitzer Master BLISS Map to Remove the Instrument-Systematic -- Phase-Curve-Parameter Degeneracy, as Demonstrated by a Reanalysis of the 4.5$μm$ WASP-43b Phase Curve

Authors: Erin M. May, Kevin B. Stevenson

Abstract: While Spitzer IRAC systematics are generally well understood, each data set can provide its own challenges that continue to teach us about the underlying functional form of these systematics. Multiple groups have analyzed the phase curves of WASP-43b with varying detrending techniques, each obtaining different results. In this work, we take another look at WASP-43b while exploring the degenerate r… ▽ More While Spitzer IRAC systematics are generally well understood, each data set can provide its own challenges that continue to teach us about the underlying functional form of these systematics. Multiple groups have analyzed the phase curves of WASP-43b with varying detrending techniques, each obtaining different results. In this work, we take another look at WASP-43b while exploring the degenerate relation between Bilinearly-Interpolated Subpixel Sensitivity (BLISS) mapping, point response function full width at half-maximum (PRF-FWHM) detrending, and phase curve parameters. We find that there is a strong correlation between the detrending parameters in the two models, and best fit phase curve amplitudes vary strongly when the data are temporally binned. To remove this degeneracy, we present a new Gaussian centroided intrapixel sensitivity map (hereafter fixed sensitivity map), generated using 3,712,830 exposures spanning 5 years, for a variety of aperture sizes at 4.5$μm$. We find evidence for time variability in the sensitivity at 3.6$μm$ and do not generate a visit-independent map for this channel. With the fixed 4.5 $μm$ intrapixel sensitivity map, the best fits for WASP-43b no longer vary strongly with bin size and PRF-FWHM detrending is no longer required to remove correlated noise. For data sets that do not fall completely within the sweet spot, temporal binning should not be used in the analysis of Spitzer phase curves. We confirm night side emission for WASP-43b with a disk integrated nightside temperature of 806 $\pm$ 48 K at 4.5$μm$. The 4.5$μm$ maps are available at \url{github.com/kevin218/POET} △ Less

Submitted 13 July, 2020; originally announced July 2020.

Comments: Submitted to AAS journals. Updated with Referee Comments. 12 pages, 7 figures, 1 table

From Super-Earths to Mini-Neptunes: Implications of a Surface on Atmospheric Circulation

Authors: Erin M May, Emily Rauscher

Abstract: It is well known that planets with radii between that of Earth and Neptune have been the most commonly detected to-date. To classify these planets as either terrestrial or gaseous, typically we turn to mass-radius relations and composition curves to determine the likelihood of such a planet being rocky or gaseous. While these methods have set a likely transition radius of approximately 1.5 R… ▽ More It is well known that planets with radii between that of Earth and Neptune have been the most commonly detected to-date. To classify these planets as either terrestrial or gaseous, typically we turn to mass-radius relations and composition curves to determine the likelihood of such a planet being rocky or gaseous. While these methods have set a likely transition radius of approximately 1.5 R$_{\oplus}$, we cannot expect that any change between terrestrial and gaseous compositions will be a sharp cut-off, and composition curve predictions result in ambiguous designations for planets right near this transition radius. In this work we present 3D general circulation models of transition planets, wherein we study the effects of a surface on observable quantities such as the latitudinal variations and eclipse depths. We present our updated GCM, validated on the circulation of Earth, before discussing our modeling choices for this transition planet. Finally, we discuss the results of this study and explore the prospects of detecting the presence of a surface through observations of secondary eclipses in the future. △ Less

Submitted 30 March, 2020; originally announced March 2020.

Comments: 15 pages, 8 figures, 3 tables. Accepted to ApJ

MOPSS II: Extreme Optical Scattering Slope for the Inflated Super-Neptune HATS-8b

Authors: E. M. May, T. Gardner, E. Rauscher, J. D. Monnier

Abstract: We present results for the inflated super-Neptune HATS-8b from MOPSS, The Michigan Optical Planetary Spectra Survey. This program is aimed at creating a database of optical planetary transmission spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. HATS-8b orbits a G dwarf and is a low density super-Neptune, with a radius of 0… ▽ More We present results for the inflated super-Neptune HATS-8b from MOPSS, The Michigan Optical Planetary Spectra Survey. This program is aimed at creating a database of optical planetary transmission spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. HATS-8b orbits a G dwarf and is a low density super-Neptune, with a radius of 0.873 R$_{Jup}$, a mass of 0.138 M$_{Jup}$, and a density of 0.259 g/cm$^3$. Two transits of HATS-8b were observed in July and August of 2017 with the IMACS instrument on the Magellan Baade 6.5m telescope. We find an enhanced scattering slope that differs between our two nights. These slopes are stronger than one due only to Rayleigh scattering and cannot be fully explained by unocculted star spots. We explore the impact of condensates on the scattering slope and determine that MnS particulates smaller than 10$^{-2}μ$m can explain up to 80\% of our measured slope if the planet is warmer than equilibrium, or 50\% of the slope at the equilibrium temperature of the planet for a low mean molecular weight atmosphere. The scattering slope that we observe is thus beyond even the most extreme case predicted by theory. We suggest further follow up on this target and host star to determine if the temporal variation of the slope is primarily due to stellar or planetary effects, and to better understand what these effects may be. △ Less

Submitted 26 September, 2018; originally announced September 2018.

Comments: 15 pages, 10 figures, 3 tables. Submitted to AJ

MOPSS I: Flat Optical Spectra for the Hot Jupiters WASP-4 b and WASP-52b

Authors: E. M. May, M. Zhao, M. Haidar, E. Rauscher, J. D. Monnier

Abstract: We present the first results from MOPSS, The Michigan Optical Planetary Spectra Survey, aimed at creating a database of optical planetary transmission spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. We discuss our methods, and present results for our first two targets observed with the Magellan Baade 6.5m telescope, one t… ▽ More We present the first results from MOPSS, The Michigan Optical Planetary Spectra Survey, aimed at creating a database of optical planetary transmission spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. We discuss our methods, and present results for our first two targets observed with the Magellan Baade 6.5m telescope, one transit of the Hot Jupiter WASP-4b and two transits of the Hot Saturn WASP-52b. Both targets present flat, featureless spectra, corresponding to the presence of aerosols. We find that the cloud decks must begin no lower than 10$^{-4}$ bar for both planets. For WASP-52b, we also consider the effects of star spots on the transmission spectrum, including unocculted spots and spots on the stellar limb influencing the light curve limb darkening parameters. We discuss the usefulness of this program in the coming James Webb Space Telescope era. △ Less

Submitted 17 July, 2018; originally announced July 2018.

Comments: 21 pages, 16 figures, 4 tables. Accepted for publication in AJ

The Transiting Exoplanet Community Early Release Science Program for JWST

Authors: Jacob L. Bean, Kevin B. Stevenson, Natalie M. Batalha, Zachory Berta-Thompson, Laura Kreidberg, Nicolas Crouzet, Björn Benneke, Michael R. Line, David K. Sing, Hannah R. Wakeford, Heather A. Knutson, Eliza M. -R. Kempton, Jean-Michel Désert, Ian Crossfield, Natasha E. Batalha, Julien de Wit, Vivien Parmentier, Joseph Harrington, Julianne I. Moses, Mercedes Lopez-Morales, Munazza K. Alam, Jasmina Blecic, Giovanni Bruno, Aarynn L. Carter, John W. Chapman , et al. (77 additional authors not shown)

Abstract: The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in unprecedented detail. However, the high-precision, time-series observations required for such investigations have unique technical challenges, and prior experience with other… ▽ More The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in unprecedented detail. However, the high-precision, time-series observations required for such investigations have unique technical challenges, and prior experience with other facilities indicates that there will be a steep learning curve when JWST becomes operational. In this paper we describe the science objectives and detailed plans of the Transiting Exoplanet Community Early Release Science (ERS) Program, which is a recently approved program for JWST observations early in Cycle 1. The goal of this project, for which the obtained data will have no exclusive access period, is to accelerate the acquisition and diffusion of technical expertise for transiting exoplanet observations with JWST, while also providing a compelling set of representative datasets that will enable immediate scientific breakthroughs. The Transiting Exoplanet Community ERS Program will exercise the time-series modes of all four JWST instruments that have been identified as the consensus highest priorities, observe the full suite of transiting planet characterization geometries (transits, eclipses, and phase curves), and target planets with host stars that span an illustrative range of brightnesses. The observations in this program were defined through an inclusive and transparent process that had participation from JWST instrument experts and international leaders in transiting exoplanet studies. Community engagement in the project will be centered on a two-phase Data Challenge that culminates with the delivery of planetary spectra, time-series instrument performance reports, and open-source data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST mission. △ Less

Submitted 3 September, 2018; v1 submitted 13 March, 2018; originally announced March 2018.

Comments: PASP in press

Examining Tatooine: Atmospheric Models of Neptune-Like Circumbinary Planets

Authors: E. M. May, E. Rauscher

Abstract: Circumbinary planets experience a time varying irradiation pattern as they orbit their two host stars. In this work, we present the first detailed study of the atmospheric effects of this irradiation pattern on known and hypothetical gaseous circumbinary planets. Using both a one-dimensional Energy Balance Model and a three-dimensional General Circulation Model, we look at the temperature differen… ▽ More Circumbinary planets experience a time varying irradiation pattern as they orbit their two host stars. In this work, we present the first detailed study of the atmospheric effects of this irradiation pattern on known and hypothetical gaseous circumbinary planets. Using both a one-dimensional Energy Balance Model and a three-dimensional General Circulation Model, we look at the temperature differences between circumbinary planets and their equivalent single-star cases in order to determine the nature of the atmospheres of these planets. We find that for circumbinary planets on stable orbits around their host stars, temperature differences are on average no more than 1.0% in the most extreme cases. Based on detailed modeling with the General Circulation Model, we find that these temperature differences are not large enough to excite circulation differences between the two cases. We conclude that gaseous circumbinary planets can be treated as their equivalent single-star case in future atmospheric modeling efforts. △ Less

Submitted 27 May, 2016; originally announced May 2016.

Comments: 9 pages, 7 figures, Accepted to ApJ

Chandra Observations of the Radio Galaxy 3C 445 and the Hotspot X-ray Emission Mechanism

Authors: Eric S. Perlman, Markos Georganopoulos, Emily M. May, Demosthenes Kazanas

Abstract: We present new {\it Chandra} observations of the radio galaxy 3C 445, centered on its southern radio hotspot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hotspot. Attempting to reproduce both the observed spectral energy distribution (SED) and the displacement, excludes all one zone models. Modeling of the radio-optical hotspot spectrum suggests… ▽ More We present new {\it Chandra} observations of the radio galaxy 3C 445, centered on its southern radio hotspot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hotspot. Attempting to reproduce both the observed spectral energy distribution (SED) and the displacement, excludes all one zone models. Modeling of the radio-optical hotspot spectrum suggests that the electron distribution has a low energy cutoff or break approximately at the proton rest mass energy. The X-rays could be due to external Compton scattering of the cosmic microwave background (EC/CMB) coming from the fast (Lorentz factor $Γ\approx 4$) part of a decelerating flow, but this requires a small angle between the jet velocity and the observer's line of sight ($θ\approx 14^{\circ}$). Alternatively, the X-ray emission can be synchrotron from a separate population of electrons. This last interpretation does not require the X-ray emission to be beamed. △ Less

Submitted 15 October, 2009; originally announced October 2009.

Comments: 9 pages, 5 figures, ApJ, in press

Journal ref: Astrophys.J.708:1-8,2010