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It means that if you average together the motion of all of the mass of the planet, it revolves once per orbit around the star. Which is the same as what it mean
by greglindahl 9y ago
It means that if you average together the motion of all of the mass of the planet, it revolves once per orbit around the star. Which is the same as what it means for a rocky planet, if you think about it, it's just a little less obvious.
Another way to think about it is that the gas giant moves such that tidal friction caused by the gravity of the star is minimized... because that's why it's moving like that.
- ChuckMcM 9y agoMakes me wonder what shape such a planet would take.
- adrianratnapala 9y agoVery slightly elongated along the axis between itself and the star. Still nearly spherical and the deviation would be essentially ellipsoidal (not egg-shaped).
- greglindahl 9y agoIt's probably a bit more exciting than that when you include evaporation and the stellar wind! But yes, an ellipsoid is the basic shape, the tides elongate the planet both towards and away from the star, same as the tides on the Earth caused by the moon.
- adrianratnapala 9y agoYep. The original post even speculates the thing might have a comet-tail because of the evaporation.
- ChuckMcM 9y agoI kind of imagine it looking sort of like a Hersey's Kiss shape :-)