2 research outputs found
Methane Throughout the Atmosphere of the Warm Exoplanet WASP-80b
The abundances of major carbon and oxygen bearing gases in the atmospheres of
giant exoplanets provide insights into atmospheric chemistry and planet
formation processes. Thermochemistry suggests that methane should be the
dominant carbon-bearing species below 1000 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, methane 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. Here we report
transmission and emission spectra spanning 2.4-4.0 micrometers of the 825 K
warm Jupiter WASP-80b taken with JWST's NIRCam instrument, both of which show
strong evidence for methane at greater than 6-sigma significance. The derived
methane abundances from both viewing geometries are consistent with each other
and with solar to sub-solar C/O and ~5 solar metallicity, which is
consistent with theoretical predictions.Comment: 23 pages, 10 figures, 3 tables. This preprint has been submitted to
and accepted in principle for publication in Nature without significant
change
A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
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 and
Spitzer Space Telescopes. 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 JWST. The
data span 0.85 to 2.85 m in wavelength at an average resolving power of
400 and exhibit minimal systematics. The spectrum shows three water emission
features (at 6 confidence) and evidence for optical opacity,
possibly due to H, TiO, and VO (combined significance of 3.8).
Models that fit the data require a thermal inversion, molecular dissociation as
predicted by chemical equilibrium, a solar heavy element abundance
(''metallicity'', M/H = 1.03 solar), and a
carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside
brightness temperature map, which shows a peak in temperature near the
sub-stellar point that decreases steeply and symmetrically with longitude
toward the terminators.Comment: JWST ERS bright star observations. Uploaded to inform JWST Cycle 2
proposals. Manuscript under review. 50 pages, 14 figures, 2 table