Publications by authors named "Michael Line"

Article Synopsis
  • HD 189733b is a key exoplanet for studying atmospheres, providing insights into composition, chemistry, and atmospheric dynamics.
  • Previous studies identified molecules like HO and CO in its atmosphere, but some findings about methane have been disputed.
  • Recent observations detect HO, CO, and HS, leading to an inferred atmosphere metallicity three to five times that of its star, suggesting formation from water-rich icy planetesimals.
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Interactions between exoplanetary atmospheres and internal properties have long been proposed to be drivers of the inflation mechanisms of gaseous planets and apparent atmospheric chemical disequilibrium conditions. However, transmission spectra of exoplanets have been limited in their ability to observationally confirm these theories owing to the limited wavelength coverage of the Hubble Space Telescope (HST) and inferences of single molecules, mostly HO (ref. ).

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The recent inference of sulfur dioxide (SO) in the atmosphere of the hot (approximately 1,100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations suggests that photochemistry is a key process in high-temperature exoplanet atmospheres. This is because of the low (<1 ppb) abundance of SO under thermochemical equilibrium compared with that produced from the photochemistry of HO and HS (1-10 ppm). However, the SO inference was made from a single, small molecular feature in the transmission spectrum of WASP-39b at 4.

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The abundances of main carbon- and oxygen-bearing gases in the atmospheres of giant exoplanets provide insights into atmospheric chemistry and planet formation processes. Thermochemistry suggests that methane (CH) should be the dominant carbon-bearing species below about 1,000 K over a range of plausible atmospheric compositions; this is the case for the solar system planets and has been confirmed in the atmospheres of brown dwarfs and self-luminous, directly imaged exoplanets. However, CH has not yet been definitively detected with space-based spectroscopy in the atmosphere of a transiting exoplanet, but a few detections have been made with ground-based, high-resolution transit spectroscopy including a tentative detection for WASP-80b (ref.

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Close-in giant exoplanets with temperatures greater than 2,000 K ('ultra-hot Jupiters') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble Space Telescope (HST) and Spitzer Space Telescope. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on the JWST.

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Article Synopsis
  • Photochemistry plays a critical role in regulating the composition and stability of planetary atmospheres, but clear photochemical products have not been detected in exoplanets until recently.* -
  • The James Webb Space Telescope (JWST) detected sulfur dioxide (SO) in the atmosphere of the exoplanet WASP-39b, suggesting photochemical processes create SO in this gas giant's atmosphere.* -
  • The presence of SO, linked to the oxidation of hydrogen sulfide, indicates WASP-39b has high metallicity (about 10 times that of the sun), and its spectral features could help understand more about similar exoplanets.*
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Article Synopsis
  • Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres helps to understand their chemical processes and formation history.
  • The James Webb Space Telescope (JWST) allows for advanced observations of exoplanets, notably WASP-39b, providing insights through time-series data with high precision in a new wavelength range.
  • Findings include the detection of water vapor in the atmosphere with a high metallicity (1-100 times that of the Sun) and a low C/O ratio, suggesting the potential for significant solid material accretion during formation or chemical disequilibrium in the atmosphere.
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The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy. However, these efforts have been hampered by modelling degeneracies between composition and cloud properties that are caused by limited data quality. Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST.

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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 the chemical inventory of an exoplanet 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 ≈ 600) transmission spectrum of an exoplanet atmosphere between 3 and 5 μm covering several absorption features for the Saturn-mass exoplanet WASP-39b (ref.

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Exoplanet science is one of the most thriving fields of modern astrophysics. A major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures in their atmospheres that indicate biological activity, assess their ability to provide conditions for life as we know it, and investigate their expected atmospheric diversity. None of the currently adopted projects or missions, from ground or in space, can address these goals.

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Measurements of the atmospheric carbon (C) and oxygen (O) relative to hydrogen (H) in hot Jupiters (relative to their host stars) provide insight into their formation location and subsequent orbital migration. Hot Jupiters that form beyond the major volatile (HO/CO/CO) ice lines and subsequently migrate post disk-dissipation are predicted have atmospheric carbon-to-oxygen ratios (C/O) near 1 and subsolar metallicities, whereas planets that migrate through the disk before dissipation are predicted to be heavily polluted by infalling O-rich icy planetesimals, resulting in C/O < 0.5 and super-solar metallicities.

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The US Army aeromedical physician assistant (PA) serves aviation units in regards to crewmember medical readiness. All PAs are graduates of a 6-week flight surgeon course. They are responsible for conducting nearly 40% of the annual US Army flight physicals.

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Exoplanets that orbit close to their host stars are much more highly irradiated than their solar system counterparts. Understanding the thermal structures and appearances of these planets requires investigating how their atmospheres respond to such extreme stellar forcing. We present spectroscopic thermal emission measurements as a function of orbital phase ("phase-curve observations") for the highly irradiated exoplanet WASP-43b spanning three full planet rotations using the Hubble Space Telescope.

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