Figure 4.
In secondary eclipse, we measure the dayside
emission spectrum of the planet as its light is
blocked by the host star. Emission spectroscopy
is sensitive to the absolute chemical
abundances and the thermal structure.
In transit, we measure the transmission spectrum of
the planet as light from the host star is absorbed by
chemical species in the planet’s atmosphere. These data
are most sensitive to the relative chemical abundances
and the presence of cloud or haze particles.
light from the host star is blocked at different altitudes in the planet’s atmosphere
due to the absorption by chemical species.
Also, measurements when transiting planets pass behind their host stars can reveal
their thermal emission and reflection spectra. Figure 4 illustrates the geometry of
transit spectroscopy observations and discusses what inf