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 Earth-like 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.
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