Kevin B. Stevenson
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View article: What's Inside Matters: The Effect of Oxygen Fugacity and Initial Volatile Abundance on the Atmospheres of the TRAPPIST-1 Planets
What's Inside Matters: The Effect of Oxygen Fugacity and Initial Volatile Abundance on the Atmospheres of the TRAPPIST-1 Planets Open
The TRAPPIST-1 planets have become prime targets for studying the atmospheric and geophysical properties of planets around M-dwarf stars. To effectively identify their atmospheric composition, we first must understand their geological evol…
View article: JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b
JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b Open
Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and nontransiting exoplanets, although the PIE technique requires empirical validation. Here, we apply t…
View article: The Photochemical Plausibility of Warm Exo-Titans Orbiting M Dwarf Stars
The Photochemical Plausibility of Warm Exo-Titans Orbiting M Dwarf Stars Open
The James Webb Space Telescope (JWST) has begun to spectrally characterize small exoplanets orbiting M dwarf stars, but interpretation of these spectra is ambiguous, with stellar, instrumental, or atmospheric origins possible for apparent …
View article: JWST-TST DREAMS: Sulfur Dioxide in the Atmosphere of the Neptune-mass Planet HAT-P-26 b from NIRSpec G395H Transmission Spectroscopy
JWST-TST DREAMS: Sulfur Dioxide in the Atmosphere of the Neptune-mass Planet HAT-P-26 b from NIRSpec G395H Transmission Spectroscopy Open
We present the James Webb Space Telescope (JWST) transmission spectrum of the exoplanet HAT-P-26 b (18.6 M ⊕ , 6.33 R ⊕ ), based on a single transit observed with the JWST NIRSpec G395H grating. We detect water vapor ( = 4.1), carbon di…
View article: Horizontal and vertical exoplanet thermal structure from a JWST spectroscopic eclipse map
Horizontal and vertical exoplanet thermal structure from a JWST spectroscopic eclipse map Open
View article: K2-18b Does Not Meet the Standards of Evidence for Life
K2-18b Does Not Meet the Standards of Evidence for Life Open
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 d…
View article: JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b
JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b Open
Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and non-transiting exoplanets, however the PIE technique requires empirical validation. Here we apply th…
View article: Heat Reveals What Clouds Conceal: Global Carbon & Longitudinally Asymmetric Chemistry on LTT 9779 b
Heat Reveals What Clouds Conceal: Global Carbon & Longitudinally Asymmetric Chemistry on LTT 9779 b Open
LTT-9779 b is an ultra-hot Neptune (Rp ~ 4.7 Re, Mp ~ 29 Me) orbiting its Sun-like host star in just 19 hours, placing it deep within the "hot Neptune desert," where Neptunian planets are seldom found. We present new JWST NIRSpec G395H pha…
View article: A first look at rocky exoplanets with JWST
A first look at rocky exoplanets with JWST Open
Rocky exoplanet characterization has been a top priority for early James Webb Space Telescope (JWST) science operations. Several milestones have been achieved, including the most precise rocky planet transmission spectra measured to date, …
View article: JWST-TST DREAMS: Sulfur dioxide in the atmosphere of the Neptune-mass planet HAT-P-26 b from NIRSpec G395H transmission spectroscopy
JWST-TST DREAMS: Sulfur dioxide in the atmosphere of the Neptune-mass planet HAT-P-26 b from NIRSpec G395H transmission spectroscopy Open
We present the James Webb Space Telescope (JWST) transmission spectrum of the exoplanet HAT-P-26 b (18.6 Earth masses, 6.33 Earth radii), based on a single transit observed with the JWST NIRSpec G395H grating. We detect water vapor (ln B =…
View article: The Photochemical Plausibility of Warm Exo-Titans Orbiting M-Dwarf Stars
The Photochemical Plausibility of Warm Exo-Titans Orbiting M-Dwarf Stars Open
The James Webb Space Telescope (JWST) has begun to spectrally characterize small exoplanets orbiting M-dwarf stars, but interpretation of these spectra is ambiguous, with stellar, instrumental, or atmospheric origins possible for apparent …
View article: Additional JWST/NIRSpec Transits of the Rocky M Dwarf Exoplanet GJ 1132 b Reveal a Featureless Spectrum
Additional JWST/NIRSpec Transits of the Rocky M Dwarf Exoplanet GJ 1132 b Reveal a Featureless Spectrum Open
As an archetypal M-dwarf rocky exoplanet, GJ 1132 b has a varied history of atmospheric measurements. At 1.13 R ⊕ , 1.66 M ⊕ , and 580 K, it orbits a bright, slowly rotating M dwarf in a 1.6 day period, making it a prime target for charact…
View article: JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e
JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e Open
TRAPPIST-1 e is one of the very few rocky exoplanets that is both amenable to atmospheric characterization and resides in the habitable zone of its star—located at a distance from its star such that it might, with the right atmosphere, sus…
View article: JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e
JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e Open
The TRAPPIST-1 system offers one of the best opportunities to characterize temperate terrestrial planets beyond our own solar system. Within the TRAPPIST-1 system, planet e stands out as highly likely to sustain surface liquid water if it …
View article: The SPACE Program
The SPACE Program Open
Sub-Neptune exoplanets are the most abundant type of planet known today. As they do not have a Solar System counterpart, many open questions exist about their composition and formation. Previous spectroscopic studies have ruled out aerosol…
View article: Stellar Models Also Limit Exoplanet Atmosphere Studies in Emission
Stellar Models Also Limit Exoplanet Atmosphere Studies in Emission Open
Stellar contamination has long been recognized as a major bottleneck in transmission spectroscopy, limiting our ability to accurately characterize exoplanet atmospheres—particularly for terrestrial worlds. In response, significant observat…
View article: Overcast Mornings and Clear Evenings in Hot Jupiter Exoplanet Atmospheres
Overcast Mornings and Clear Evenings in Hot Jupiter Exoplanet Atmospheres Open
Aerosols are an old topic in the young field of exoplanet atmospheres. Understanding what they are, how they form, and where they go has long provided a fertile playground for theorists. For observers, however, aerosols have been a multide…
View article: The Era on Non-Transiting Habitable Zone Terrestrial Planets Around M-dwarfs
The Era on Non-Transiting Habitable Zone Terrestrial Planets Around M-dwarfs Open
Recent exoplanet surveys from the ground have discovered myriad nearby planetary systems around M- dwarfs (Teff < ~3600K), most of which are non-transiting. While transit methods have made advances in characterizing the atmospheres of plan…
View article: NIRCam Yells at Cloud: JWST MIRI Imaging Can Directly Detect Exoplanets of the Same Temperature, Mass, Age, and Orbital Separation as Saturn and Jupiter
NIRCam Yells at Cloud: JWST MIRI Imaging Can Directly Detect Exoplanets of the Same Temperature, Mass, Age, and Orbital Separation as Saturn and Jupiter Open
NIRCam and MIRI coronagraphy has successfully demonstrated the ability to directly image young sub-Jupiter-mass and mature gas giant exoplanets. However, these modes struggle to reach the sensitivities needed to find the population of cold…
View article: Statistical Trends in JWST Transiting Exoplanet Atmospheres
Statistical Trends in JWST Transiting Exoplanet Atmospheres Open
Our brains are hardwired for pattern recognition as correlations are useful for predicting and understanding nature. As more exoplanet atmospheres are being characterized with JWST, we are starting to unveil their properties on a populatio…
View article: The James Webb Space Telescope NIRSpec-PRISM Transmission Spectrum of the Super-Puff, Kepler-51d
The James Webb Space Telescope NIRSpec-PRISM Transmission Spectrum of the Super-Puff, Kepler-51d Open
Kepler-51 is a 500 Myr G dwarf hosting three "super-puffs" and one low-mass non-transiting planet. Kepler-51d, the coolest (T_eq ~ 350 K) transiting planet in this system, is also one of the lowest density super-puffs known to date (rho_p …
View article: NIRCam yells at cloud: JWST MIRI imaging can directly detect exoplanets of the same temperature, mass, age, and orbital separation as Saturn and Jupiter
NIRCam yells at cloud: JWST MIRI imaging can directly detect exoplanets of the same temperature, mass, age, and orbital separation as Saturn and Jupiter Open
NIRCam and MIRI coronagraphy have successfully demonstrated the ability to directly image young sub-Jupiter mass and mature gas-giant exoplanets. However, these modes struggle to reach the sensitivities needed to find the population of col…
View article: Cloudy mornings and clear evenings on a giant extrasolar world
Cloudy mornings and clear evenings on a giant extrasolar world Open
Aerosols are common in exoplanet atmospheres, but their formation-whether through gas condensation or photochemical reactions-remains uncertain. We report a 6$σ$ detection of limb asymmetry in the transmission spectrum of WASP-94A b, revea…
View article: The Radiative Effects of Photochemical Hazes on the Atmospheric Circulation and Phase Curves of Sub-Neptunes
The Radiative Effects of Photochemical Hazes on the Atmospheric Circulation and Phase Curves of Sub-Neptunes Open
Measuring the atmospheric composition of hazy sub-Neptunes like GJ 1214b through transmission spectroscopy is difficult because of the degeneracy between mean molecular weight (MMW) and haziness. It has been proposed that phase-curve obser…
View article: Thermal Emission and Confirmation of the Frigid White Dwarf Exoplanet WD 1856+534 b
Thermal Emission and Confirmation of the Frigid White Dwarf Exoplanet WD 1856+534 b Open
We report the detection of thermal emission from and confirm the planetary nature of WD 1856+534 b, the first transiting planet known to orbit a white dwarf (WD) star. Observations with JWST’s Mid-Infrared Instrument reveal excess mid-infr…
View article: Refractory and Volatile Species in the UV-to-IR Transmission Spectrum of Ultra-hot Jupiter WASP-178b with HST and JWST
Refractory and Volatile Species in the UV-to-IR Transmission Spectrum of Ultra-hot Jupiter WASP-178b with HST and JWST Open
The atmospheres of ultra-hot Jupiters are unique compared to other planets because of the presence of both refractory and volatile gaseous species, enabling a new lens to constrain a planet’s composition, chemistry, and formation. WASP-178…
View article: Thermal Emission and Confirmation of the Frigid White Dwarf Exoplanet WD 1856+534b
Thermal Emission and Confirmation of the Frigid White Dwarf Exoplanet WD 1856+534b Open
We report the detection of thermal emission from and confirm the planetary nature of WD 1856+534b, the first transiting planet known to orbit a white dwarf star. Observations with JWST's Mid-Infrared Instrument (MIRI) reveal excess mid-inf…
View article: HST SHEL: Revealing Haze and Confirming Elevated Metallicity in the Warm Neptune HAT-P-26b
HST SHEL: Revealing Haze and Confirming Elevated Metallicity in the Warm Neptune HAT-P-26b Open
We present a new and extended transmission spectrum of the warm Neptune HAT-P-26b spanning wavelengths between 0.29 and 5.0 μ m. This spectrum is derived from new HST STIS G430L observations from the PanCET program, a reanalysis of the pre…
View article: An Analysis of Spitzer Phase Curves for WASP-121b and WASP-77Ab
An Analysis of Spitzer Phase Curves for WASP-121b and WASP-77Ab Open
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 ± 95 ppm (3.6 μ m) and 2048 ± 109 ppm (4.5 μ m), an…
View article: Eclipse Mapping with MIRI: 2D Map of HD 189733b from 8 <i>μ</i>m JWST MIRI LRS Observations
Eclipse Mapping with MIRI: 2D Map of HD 189733b from 8 <i>μ</i>m JWST MIRI LRS Observations Open
Observations and models of transiting hot Jupiter exoplanets indicate that atmospheric circulation features may cause large spatial flux contrasts across their daysides. Previous studies have mapped these spatial flux variations through in…