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.
Highlights
Water ice is an important building block for planet formation under the core accretion paradigm (Pollack et al 1996)
The measured abundance of CO2 is relatively high compared to the expected thermochemical value for a solar composition gas (∼5 × 10−8)
We show the probability distributions of water abundances measured from the emission spectrum and transmission spectrum
Summary
McCullough, Sara Seager, Adam Burrows, Gregory W.
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