How would a gas giant have such temperature extremes?

Question

The Ken Than article in space.com also on CNN.com tells about an exoplanet (around a star other than our own) that is a "gas giant" around Upsilon Andromeda, a star some 40 light years away.  The trick is that it seemingly has a sunlit side temperature between 2500 and 3000 F (1400-1650 C) and -4 to -450 F on the dark side (they think it is tidally locked, so the same side always faces its star).  The planet has a "tight orbit" and goes around every 4.6 days.

If it is a "gas" giant, and the gas is heated to some 3k F, how can it have such a cold other side.  I can see that for a rocky planet, but gases expand and move when hot, and condense and sink when cold.  Why would there be no circulation that moderates the temperatures?  Any ideas? http://www.cnn.com/2006/TECH/space/10/13/fire.ice.planet/index.html

extton · Accepted Answer

There is circulation.

But you have to understand just how large such a gas giant is.

You know that giant red spot on jupiter? It's a storm. But do you know how big it is? You could fit the entire planet earth inside of that storm, with room to spare.

The gas giants we find in other solar systems are even bigger than jupiter. 
So, while warm and cold gasses sure do circulate, by the time any given bunch of gas has made it from one side of the planet to the other, it has either absorbed a lot of energy from the sun, or radiated all of it away into space.

 Thus, the temperatures on opposite sides of the planet stay more or less constant.

Anonymous · Answer

Gas is not a good conductor of heat.

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How would a gas giant have such temperature extremes?

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