 Exoplanet thermal phase curve

An exoplanet thermal phase curve measures the change in planetary infrared brightness through the orbit, after modelling the host star's contribution. Around exoplanet secondary eclipse the visible hemisphere is mostly dayside; around primary exoplanet transit it is mostly nightside. The amplitude therefore constrains the longitudinal thermal contrast, while an offset maximum indicates an asymmetric brightness distribution.

Spitzer Space Telescope observations of HD 189733 b demonstrated that this technique could constrain day-night heat redistribution and a displaced bright region even without resolving the planetary disc.^[ref] A phase curve averages light over a visible hemisphere. Its map is therefore model-dependent, and brightness temperatures in one band need not describe all atmospheric pressures.