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

Interactions between exoplanetary atmospheres and internal properties have long been hypothesized to be drivers of the inflation mechanisms of gaseous planets and apparent atmospheric chemical disequilibrium conditions 1 . However, transmission spectra of exoplanets has been limited in its ability to observational confirm these theories due to the limited wavelength coverage of HST and inferences of single molecules, mostly H 2 O (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 WFC3, JWST NIRCam and MIRI. From this spectrum, we detect spectroscopic features due to H 2 O (21σ), CH 4 (5σ), CO (7σ), CO 2 (29σ), SO 2 (9σ), and NH 3 (6σ). The presence of these molecules enable constraints on the atmospheric metal enrichment (M/H is 10-18× Solar 3 ), vertical mixing strength (log 10 K zz  = 8.4-9.0 cm 2 s -1 ), and internal temperature (>345 K). The high internal temperature is suggestive of tidally-driven inflation 4 acting upon a Neptunelike internal structure, which can naturally explain the planet's large radius and low density. These findings suggest that eccentricity driven tidal heating is a critical process governing atmospheric chemistry and interior structure inferences for a majority of the cool (<1,000K) super-Earth-to-Saturn mass exoplanet population.