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

Exoplanet Thermal Light

There are a variety of methods to model the thermal light emitted by hot exoplanets. First, the exoplanet is treated as if areas of it emit light like a blackbody, which means that hotter areas emit more light than cooler areas. From this idea, we see that the thermal light of exoplanets depends on the temperature distribution across its surface, or the top of its atmosphere. The earliest modeling of exoplanets only calculated a single brightness temperature, and two zone (or day/nightside) models soon followed.

A wide variety of thermal models now exist, but EXONSET makes use of two with a third is development. The first, is the simplest two zone model. The second model assumes that the planet can be treated as having N distinct temperature zones each of which is a different temperature. The model than calculates the thermal emissions of each zone as a function of time, the radius of the exoplanet, the number of zones, and their temperatures. The total thermal light is the summation from each zone. The zones in this case are distributed as spherical segments aligned axially with the substellar point and center of the exoplanet, where the zone closest to the host star is hottest, and that farthest is coolest. Future work for this model includes accounting for rotation, and a hotspot offset.

A multi-coloured sphere.
Cartoon depicting the axially symmetric temperature distribution with eight zones.

Work is ongoing to incorporate a model developed by Cowan and Agol in 2008, which treats the exoplanet as if the temperature is distributed as N-zones which look like orange slices or the sections of a beach ball. This model does not account for rotation but does include a hotspot offset.

People involved with this project

  • Jenn Carter – Theory and management
  • Michelle Arrigo – Extended N-zone model to work with two to six zones, began work to work with any number of zones
  • Jocelyn McMahon – Initial coding of N-zone model

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