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4

The distinction between gas giants and ice giants is a distinction that works nicely in our solar system. (And don't forget the distinction between the giant planets and the terrestrial planets, which also works nicely in our solar system.) I strongly doubt that these distinctions are universal. Just before the end of the 20th century, astronomers and ...

3

The paper proposes the magnetic coupling of a central object to the accretion disc from which it is building up its mass. This is thought to be the same route by which low-mass stars are prevented from spinning up to break-up speeds during their formation. The idea is to imagine a bar magnet in the planets with a dipole field. The field emerges from the ...

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The slowdown is due to 'angular momentum transfer' from inner regions of the rotating cloud to outer regions via magnetic fields. You can find a detailed mathematical explanation in terms of a solution of the MHD- equation on this web page http://th.nao.ac.jp/MEMBER/tomisaka/Lecture_Notes/StarFormation/5/node94.html . It may not be easy to fully understand ...

8

The gravitational force on a small mass on the outside of a planet is always the Newtonian $$F_{G}=-\frac{GM}{r^2},$$ so any planet, and particularly, any mass in the universe produces a gravitational field acting on everything else. So if, for example, the mass is $M=2\times 10^{27}\rm kg$ (i.e. one Jovian mass), then the gravity field outside the planet ...

5

Anything with mass has gravity, so yes, such a planet would have gravity. However, gases tend to disperse in their surrounding environment, so you’d need a very massive gas cloud to collapse into such a planet for gases not to disperse. This raises the question of the pressure at the centre of this planet; it would be high enough to turn the gas at least ...

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