Circumbinary planets are planets that orbit two host stars.
As a result, they experience a time-varying irradiation pattern. Circumbinary
planets appear to be relatively common. It has been predicted that planets
larger than 6 times the radius of Earth occur for at least 10 percent of
circumbinary systems. A number of circumbinary planets have already been
detected and most of them are around the size of Neptune.
Figure 1: Artist’s impression of a circumbinary planet.
May & Rauscher (2016) present a study of the atmospheric
effects of the time-varying irradiation pattern on known and hypothetical
gaseous Neptune-like circumbinary planets. In the study, the parameter η
defines the difference in temperature for the circumbinary case as compared to
the single-star case. The results from the study show that for circumbinary
planets on stable orbits around their host stars, η does not exceed 1 percent
even for the most extreme cases.
For example, Kepler-47b is a Neptune-sized planet in a 49.5
day orbit around a pair of stars. For Kepler-47b, η is only 0.2 percent. This
means that the maximum temperature deviation from the single-star model is only
6 K. Basically, such temperature differences are not large enough to induce
discernable changes in the atmospheric circulation between circumbinary planets
and planets orbiting single stars. This means that Neptune-like circumbinary
planets can be treated as planets orbiting single stars when it comes to
atmospheric modelling.
Figure 2: η values for 7 of the 10 known circumbinary
systems. All have η values less than 0.1 percent. May & Rauscher (2016)
Reference:
May & Rauscher (2016), "Examining Tatooine:
Atmospheric Models of Neptune-Like Circumbinary Planets", arXiv:1605.08785
[astro-ph.EP]