A high internal heat flux and large core in a warm Neptune exoplanet

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 conditions1. 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 H2O (ref. 2). In this work, we present the panchromatic transmission spectrum of the approximately 750 K, low-density, Neptune-sized exoplanet WASP-107b using a combination of HST Wide Field Camera 3 (WFC3) and JWST Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). From this spectrum, we detect spectroscopic features resulting from H2O (21σ), CH4 (5σ), CO (7σ), CO2 (29σ), SO2 (9σ) and NH3 (6σ). The presence of these molecules enables constraints on the atmospheric metal enrichment (M/H is 10-18× solar3), vertical mixing strength (log10Kzz = 8.4-9.0 cm2 s-1) and internal temperature (>345 K). The high internal temperature is suggestive of tidally driven inflation4 acting on a Neptune-like internal structure, which can naturally explain the large radius and low density of the planet. These findings suggest that eccentricity-driven tidal heating is a critical process governing atmospheric chemistry and interior-structure inferences for most of the cool (<1,000 K) super-Earth-to-Saturn-mass exoplanet population.

Methane throughout the atmosphere of the warm exoplanet WASP-80b

The abundances of main carbon- and oxygen-bearing gases in the atmospheres of giant exoplanets provide insights into atmospheric chemistry and planet formation processes1,2. Thermochemistry suggests that methane (CH4) should be the dominant carbon-bearing species below about 1,000 K over a range of plausible atmospheric compositions3; this is the case for the solar system planets4 and has been confirmed in the atmospheres of brown dwarfs and self-luminous, directly imaged exoplanets5. However, CH4 has not yet been definitively detected with space-based spectroscopy in the atmosphere of a transiting exoplanet6-11, but a few detections have been made with ground-based, high-resolution transit spectroscopy12,13 including a tentative detection for WASP-80b (ref. 14). Here we report transmission and emission spectra spanning 2.4-4.0 μm of the 825 K warm Jupiter WASP-80b taken with the NIRCam instrument of the JWST, both of which show strong evidence of CH4 at greater than 6σ significance. The derived CH4 abundances from both viewing geometries are consistent with each other and with solar to sub-solar C/O and around five times solar metallicity, which is consistent with theoretical predictions15-17.

Revealing the atmospheres of highly irradiated exoplanets: from ultra-hot Jupiters to rocky worlds

Spectroscopy of transiting exoplanets has revealed a wealth of information about their atmospheric compositions and thermal structures. In particular, studies of highly irradiated exoplanets at temperatures much higher than those found in our solar system have provided detailed information on planetary chemistry and physics because of the high level of precision which can be obtained from such observations. Here we use a variety of techniques to study the atmospheres of highly irradiated transiting exoplanets and address three large, open questions in exoplanet atmosphere spectroscopy. First, we use secondary eclipse and phase curve observations to investigate the thermal structures and heat redistribution of ultra-hot Jupiters, the hottest known exoplanets. We demonstrate how these planets form an unique class of objects influenced by high-temperature chemical effects such as molecular dissociation and H^- opacity. Second, we use observations of helium in the upper atmosphere of the exo-Neptune HAT-P-11b to probe atmospheric escape processes. Third, we develop tools to interpret JWST observations of highly irradiated exoplanets, including a data analysis pipeline to perform eclipse mapping of hot Jupiters and a method to infer albedos of and detect atmospheres on hot, terrestrial planets. Finally, we discuss remaining open questions in the field of highly irradiated exoplanets and opportunities to advance our understanding of these unique bodies in the coming years.