The upper atmosphere of the exoplanet HD209458b revealed by the sodium D lines (A. Vidal-Madjar et al.)

Vol. 527In section 10. Planets and planetary systems

The upper atmosphere of the exoplanet HD209458b revealed by the sodium D lines. Temperature-pressure profile, ionization layer, and thermosphere

Vidal-Madjar and collaborators use the profile of the sodium lines to infer the stratospheric to exospheric temperature-pressure profile in exoplanet HD209458b. This ingenious method is based on the hypotheses that sodium is the only absorber in the considered spectral window and that its line profile is well-known and depends on temperature. By inverting HST transit measurements in the sodium band, they can constrain the temperature as a function of pressure in the atmosphere. The resulting profile is compatible with temperature profiles obtained with aeronomical models including hydrodynamical escape.