A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b

TL;DR

This paper measures the water abundance in the atmosphere of exoplanet WASP-43b using Hubble data, finding it consistent with solar composition and supporting trends in planetary metallicity related to mass.

Contribution

It provides a precise water abundance measurement for a hot Jupiter, linking atmospheric metallicity to planetary mass and formation models.

Findings

Water abundance is consistent with solar composition at planetary temperatures.

WASP-43b's metallicity aligns with Solar System trends of lower enrichment in higher mass planets.

Supports core accretion model predictions for exoplanet atmospheres.

Abstract

The water abundance in a planetary atmosphere provides a key constraint on the planet's primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the Solar System giant planets is not well known because water is sequestered in clouds deep in their atmospheres. By contrast, short-period exoplanets have such high temperatures that their atmospheres have water in the gas phase, making it possible to measure the water abundance for these objects. We present a precise determination of the water abundance in the atmosphere of the 2 $M_\mathrm{Jup}$ short-period exoplanet WASP-43b based on thermal emission and transmission spectroscopy measurements obtained with the Hubble Space Telescope. We find the water content is consistent with the value expected in a solar composition gas at planetary temperatures (0.4-3.5x solar at 1 $\sigma$ confidence). The metallicity of WASP-43b's atmosphere suggested by this result extends the trend observed in the Solar System of lower metal enrichment for higher planet masses.