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We report near-infrared spectroscopy of the gas giant planet HD 189733b intransit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) withits G141 grism covering 1.1 um to 1.7 um and spatially scanned the image acrossthe detector at 2\arcsec$s^{-1}$. When smoothed to 75 nm bins, the local maximaof the transit depths in the 1.15 um and 1.4 um water vapor featuresrespectively are 83+/-53 ppm and 200+/-47 ppm greater than the local minimum at1.3 um. We compare the WFC3 spectrum with the composite transit spectrum of HD189733b assembled by Pont et al. (2013), extending from 0.3 um to 24 um.Although the water vapor features in the WFC3 spectrum are compatible with themodel of non-absorbing, Rayleigh-scattering dust in the planetary atmosphere(Pont et al. 2013), we also re-interpret the available data with a clearplanetary atmosphere. In the latter interpretation, the slope of increasingtransit depth with shorter wavelengths from the near infrared, through thevisible and into the ultraviolet is caused by unocculted star spots, with asmaller contribution of Rayleigh scattering by molecular hydrogen in theplanet's atmosphere. At relevant pressures along the terminator, our modelplanetary atmosphere's temperature is ~700 K, which is below the condensationtemperatures of sodium- and potassium-bearing molecules, causing the broadwings of the spectral lines of Na I and K I at 0.589 um and 0.769 um to beweak.

Water Vapor in the Spectrum of the Extrasolar Planet HD 189733b: 1. the Transit