H ₂ O ABUNDANCES IN THE ATMOSPHERES OF THREE HOT JUPITERS

Abstract

The core accretion theory for giant planet formation predicts enrichment of\nelemental abundances in planetary envelopes caused by runaway accretion of\nplanetesimals, which is consistent with measured super-solar abundances of C,\nN, P, S, Xe, and Ar in Jupiter's atmosphere. However, the abundance of O which\nis expected to be the most dominant constituent of planetesimals is unknown for\nsolar system giant planets, owing to the condensation of water in their\nultra-cold atmospheres, thereby posing a key unknown in solar system formation.\nOn the other hand, hundreds of extrasolar hot Jupiters are known with very high\ntemperatures (>~1000 K) making them excellent targets to measure H2O abundances\nand, hence, oxygen in their atmospheres. We constrain the atmospheric H2O\nabundances in three hot Jupiters (HD 189733b, HD 209458b, and WASP-12b),\nspanning a wide temperature range (1200-2500 K), using their near-infrared\ntransmission spectra obtained using the HST WFC3 instrument. We report\nconclusive measurements of H2O in HD 189733b and HD 209458b, while that in\nWASP-12b is not well constrained by present data. The data allow nearly solar\nas well as significantly sub-solar abundances in HD 189733b and WASP-12b.\nHowever, for HD 209458b, we report the most precise H2O measurement in an\nexoplanet to date that suggests a ~20-135 sub-solar H2O abundance. We discuss\nthe implications of our results on the formation conditions of hot Jupiters and\non the likelihood of clouds in their atmospheres. Our results highlight the\ncritical importance of high-precision spectra of hot Jupiters for deriving\ntheir H2O abundances.\n