An Atomic Spectral Survey of WASP-76b: Resolving Chemical Gradients and Asymmetries

TL;DR

This study conducts a detailed spectral survey of the ultra-hot Jupiter WASP-76b, detecting multiple atomic species and analyzing atmospheric asymmetries to understand its dynamic weather patterns and chemical distribution.

Contribution

It reports the first detection of several atoms and ions in WASP-76b's atmosphere and explores the causes of observed spectral asymmetries, advancing understanding of atmospheric processes in ultra-hot Jupiters.

Findings

Detection of multiple atoms and ions, including first reports of V, Cr, Ni, Sr II, and Co in this planet.

Observation of asymmetric spectral signals linked to atmospheric condensation, ionization, and wind patterns.

Evidence supporting a two-zoned atmospheric model with different dynamics in upper and lower layers.

Abstract

Ultra-hot Jupiters are gas giants that orbit so close to their host star that they are tidally locked, causing a permanent hot dayside and a cooler nightside. Signatures of their nonuniform atmospheres can be observed with high-resolution transit transmission spectroscopy by resolving time-dependent velocity shifts as the planet rotates and varying areas of the evening and morning terminator are probed. These asymmetric shifts were seen for the first time in iron absorption in WASP-76b. Here, we search for other atoms/ions in the planet's transmission spectrum and study the asymmetries in their signals. We detect Li I, Na I, Mg I, Ca II, V I, Cr I, Mn I, Fe I, Ni I, and Sr II, and tentatively detect H I, K I, and Co I, of which V, Cr, Ni, Sr II, and Co have not been reported before. We notably do not detect Ti or Al, even though these species should be readily observable, and hypothesize this could be due to condensation or cold trapping. We find that the observed signal asymmetries in the detected species can be explained in different ways. We find a relation between the expected condensation or ionization temperatures and the strength of the observed asymmetry, which could indicate rain-out or recombination on the nightside. However, we also find a dependence on the signal broadening, which could imply a two-zoned atmospheric model, in which the lower atmosphere is dominated by a day-to-night wind, while the upper atmosphere is dominated by a vertical wind or outflow. These observations provide a new level of modeling constraint and will aid our understanding of atmospheric dynamics in highly irradiated planets.