Abstract DGP2026-23

Planets orbiting their host stars are illuminated by their stars. Therefore, they have a dayside and a nightside with different properties - and a twilight zone. Analysis of phase curves of exoplanets are rarely take care for this twilight zone. In case of the Earth-Sun System, 50% of Earth surface area is due to the dayside, 39% is nightside and 21% is in the twilight-zone. The area of the twilight-zone (partly illuminated zone), therefore, is not negligible.

The area of the twilight zone is bigger for planets closer to their host star because of simple geometrical reason. Also, zones where only part of the stellar disc instead of the full disc of the star illuminates the planet surface ('penumbral effects'). 

 

The extend of the twilight zone depends on the star-planet distance and radius ratio and also on the characteristics of the planetary atmosphere (scale height, density, composition, mass of the atmosphere). Therefore, it provides an additional opportunity to study planetary atmosphere properties.

 

In this talk I will review the significance of including the twilight-zone into planetary phase curves. I will show the commonly used phase curve-types and how they miss pieces of information in the presence of a twilight zone. I will call the attention that PLATO is able to detect the existence of such twilight zones under certain circumstances. Inclusion of twilight zones not only increases the number of observables of exoplanets, but it is needed to correctly and accurately interpret future PLATO photometric data.