Assertion: planet's moon | /r/HasProperty | proteus
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text: Heat energy, from gravitational collapse, impacts, tidal forces such as orbital resonances, or radioactive decay, also factors into whether an object will be ellipsoidal or not; Saturn's icy moon Mimas is ellipsoidal (though no longer in hydrostatic equilibrium), but Neptune's larger moon Proteus, which is similarly composed but colder because of its greater distance from the Sun, is irregular.