This is one version of test. The tilt of the Earth causes the sunlight to be more direct on one hemisphere than the other hemisphere. Over ten times larger than planet Earth. The primary source of geologic activity, volcanoes and earthquakes, on Io is radioactive decay.
Ice has a lower melting point than rock.
Start with interstellar cloud of gas and dust. Starts collapsing because of shockwave from nearby supernova or similar. The shockwave makes a region more dense so that the gravity of that dense area starts attracting nearby particles, making it even more dense and massive. The region of the cloud starts collapsing as the gravitational force gets stronger than the pressure of the gas. As it collapses, angular momentum must be conserved so that as the radius of the cloud gets smaller, the cloud has to speed up its rotation.