not detected. The enhancement of methane instead of carbon monoxide thus brought a challenge to the understanding of chemical processes in the atmosphere of the planet, and possibly of other hot Jupiters. HD 189733b was again observed with NICMOS during an eclipse [@Swain2009b]. Water, carbon monoxide, and carbon dioxide were identified in the dayside spectrum of the planet, and the mixing ratio of these molecules was derived. Observations of the hot Jupiter HD 209458b revealed a dayside spectrum dominated by methane and water features, with smaller contribution from carbon dioxide [@Swain2009a]. Their analysis also confirmed the existence of a temperature inversion in the atmosphere of the planet. Several solutions were found plausible for the molecular abundances. NICMOS transmission spectroscopy was also used to probe the atmosphere of the hot Jupiter XO-1b [@Tinetti2010]. The extracted spectrum for XO-1b shows absorption features at a level of $\sim$300 ppm, interpreted as an atmosphere containing carbon dioxide, water, methane and possibly carbon monoxide.

However, several studies show that the amplitude of NICMOS systematics remaining after the analysis are comparable to the planet’s expected signal. As an example, models for the hot-Neptune GJ-436b predict that water vapor will be present in the upper atmosphere at 