A large star is on left with the illumination of an exoplanet shown on the right over a star background.

Exoplanet Reflection

Whenever light strikes a surface, some of it may be absorbed, and some of it is reflected. The light reflected by exoplanets allows researchers to estimate composition based on the planet’s reflectivity. With more advanced instruments, researchers can also study large scale surface features based on what is called albedo mapping. For example, ice caps have a larger albedo than oceans, and will appear brighter on an albedo map.

In addition, the absorbed light contributes to the temperature of the exoplanet, so that the Thermal Light and reflected light are related. In other words, incorrectly modeling the reflected light may lead to incorrect temperature estimates.

The goal of this project is to properly account for illumination due to stars of finite angular size (see Exoplanet Illumination for more) in reflected light models, which largely make use of the plane parallel ray model. When exoplanets are extremely close to their host star, areas within the hemisphere facing away from their host star are illuminated, which is not considered by the plane parallel ray model. The far side of the exoplanet will now reflect light toward observers during most of its orbit, including when it is transiting its host star. Neglecting this light could result in underestimating the size of the exoplanet, or overestimating its nightside temperature.

The reflected light as a function of time from the fully illuminated zone, which receives light from the entire apparent disk of the host star, has been approximated. Ongoing work is required to approximate the light reflected by the penumbral zone, within which light is received from less of the host star than the fully illuminated zone.

People involved with this project

Links to papers, posters, and presentations related to this project