I have a couple comments I would like to make.
@Fiah: Because sand reflects more light than ocean, more radiation is reflected into space. A higher albedo actually cools the planet.
@Shoe: Circumbinary planets would actually experience less ultraviolet flux than planets around a single star. This is because the smaller and less luminous a main sequence star is, the less of its total light output is UV. Hence, two 0.84 solar mass stars would have the same combined luminosity of the sun, but emit less UV.
However, tidal or magnetic field interactions between the stars might increase flares or similar activity which would put stress on the magnetic field of the planet.
@smjames: This is a valid point: circumbinary planets would undergo temperature swings due to varying insolation. However, so do planets that orbit single stars (how much sunlight does the night side of Earth recieve?). The insolation changes from stellar position would last longer, but be much less intense than the changes resulting from the planet's rotation.
According to your reasoning, the Earth's rotation should be like going through the seasons every 24 hours, creating huge climatic chaos. But this doesn't happen. Why?
Well, the Earth's atmosphere and oceans have a LOT of thermal inertia. In fact, the hottest and coldest times of the year (in the northern hemisphere) are in January and July - a whole month after the solstices - because it takes so long for the planet to actually cool down. In general, the stars in a system with a habitable circumbinary planet will have an orbital period of significantly less than this. In short, the actual temperature flux will be much less than the 10 K predicted by comparing the equilibrium temperatures.
Now, there are points on Earth that do experience day/night temperature changes of well over 10 K: deserts. Because there's less water vapor in desert air, the greenhouse effect is reduced, and temperature changes are larger. However, these temperature changes do not result in "climatic chaos." In fact, the temperature cycling is pretty predictable, and life can easily adapt (for example, many desert animals are nocturnal to avoid high temperatures during the day, and many plants shut down during the hottest parts of the day to save water.
The effect eclipses would have on climate would be negligible: eclipses would be brief, and if the planet's orbit was inclined relative to that of the stars by more than a few degrees, they would only occur twice a year:
Note: the intensity of temperature changes would be affected by two main factors. First, the closer together the stars are, the less the luminosity change (each star's distance from the planet changes less) and the shorter the duration of the cycle (smaller separation = shorter orbital period). Second, the greater the thermal inertia of the planet (more ocean, higher average temperature (which results in more water vapor in the atmosphere, causing a stronger greenhouse effect), higher atmospheric pressure, and higher concentrations of greenhouse gases like carbon dioxide and methane all increase thermal inertia), the less the temperature change. So, desert planets like Tatooine would have fairly large temperature changes, while ocean planets like Kepler 22b would have almost none.
In general, whether the planet orbits one star or two affects climate much less than axis tilt and orbital eccentricity.
Topic: Discussion On The Habitability Of Binary Systems. (Read 8772 times)
