What if the asteroid belt is an exploded planet that had oceans with salt in it?
Every atom of every molecule on Earth and the Sun and all the planets and asteroids came from somewhere else. All the metals found on Earth and elsewhere were created inside a star’s furnace. When that star went nova or supernova, as the case may be, all that material was flung out into space to eventually coalesce into our Sun and its planetary retinue, to continue the cycle once again................
More likely that two roughly Mars sized planets collided, something similar happened here, giving us the Moon.
But let's suppose it did explode. How?
According to the current model of planetary formation when a pile o' rocks gets big enough mutual gravity squishes them down, the pressure and radioactive decay of some of the elements melts them together.
Heavier elements gravitate to the center.
Uranium is heavy.
Could it be possible that enough uranium ends up in close proximity to do the 'splody thing?