  Using the NICMOS instrument on the Hubble Space Telescope, we have measured
the dayside spectrum of HD 209458b between 1.5--2.5 microns. The emergent
spectrum is dominated by features due to the presence of methane (CH4) and
water vapor (H2O), with smaller contributions from carbon dioxide (CO2).
Combining this near-infrared spectrum with existing mid-infrared measurements
shows the existence of a temperature inversion and confirms the interpretation
of previous photometry measurements. We find a family of plausible solutions
for the molecular abundance and detailed temperature profile. Observationally
resolving the ambiguity between abundance and temperature requires either (1)
improved wavelength coverage or spectral resolution of the dayside emission
spectrum, or (2) a transmission spectrum where abundance determinations are
less sensitive to the temperature structure.
