The Equilibrium Temperature of Planets in Elliptical Orbits
Abstract
There exists a positive correlation between orbital eccentricity and the average stellar flux that planets receive from their parent star. Often, though, it is assumed that the average equilibrium temperature would correspondingly increase with eccentricity. Here, we test this assumption by calculating and comparing analytic solutions for both the spatial and temporal averages of orbital distance, stellar flux, and equilibrium temperature. Our solutions show that the average equilibrium temperature of a planet, with a constant albedo, slowly decreases with eccentricity until converging to a value 90% that of a circular orbit. This might be the case for many types of planets (e.g., hot Jupiters); however, the actual equilibrium and surface temperature of planets also depend on orbital variations of albedo and greenhouse. Our results also have implications in understanding the climate, habitability, and the occurrence of potential Earthlike planets. For instance, it helps explain why the limits of the habitable zone for planets in highly elliptical orbits are wider than expected from the mean flux approximation, as shown by climate models.
 Publication:

The Astrophysical Journal
 Pub Date:
 March 2017
 DOI:
 10.3847/20418213/aa5f13
 arXiv:
 arXiv:1702.07314
 Bibcode:
 2017ApJ...837L...1M
 Keywords:

 astrobiology;
 methods: analytical;
 planets and satellites: atmospheres;
 planets and satellites: fundamental parameters;
 radiation mechanisms: thermal;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 13 pages, 3 figures, 2 tables. ApJL, 837, L1