Why would a planet be spinning fast enough to fly apart?

In a comment to this question imallett brought up the idea of a gas giant spinning so fast that the air is moving at near orbital velocity.

In Mission of Gravity Hal Clement has Mesklin spin so fast that it's strongly oblate and has 700G at the poles and 3G at the equator. That's most of the way to 0G due to spin! Clement did not offer any explanation for how his planet came to be that way.

If planet were a gas giant or ice giant or something like that (as opposed to rocky) you can get differential rotation, too. Would the gas envelope rise so easily due to centrifugal effects that it would fly off before it could achieve this speed or could it spin with a speed that's within the speed of sound of the orbital velocity?

The main thing is: what would make it spin so fast? I know other bodies like stars can be spun up to high speed. What kind of history or astrophysical situation could possibly result in a planet spinning so fast?

I'd entertain ideas featuring other kinds of "planets" as long as it has a substantial atmosphere. So brown dwarfs etc. are OK.

Edit: Note that a catastrophic origin is OK. After all, look what happened to our own planet to form the moon. I don't mean a planet has to be given this rotation without wrecking it; I mean it formed that way or settled down millions or billions of years after being wrecked.

posted almost 8 years ago

JDługosz‭

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