This is Juno, an object with similar dimensions to out hypothetical planetoid.
It is not round, but there was probably some melting in its interior in the early stages.
50 MT nuclear bomb will not disperse even a smaller rubble pile. That's not how nuclear weapons work in vacuum. They can only give off heat radiation which can heat up the surface and then it can vaporize so spallation occurs, making a push through reaction force.
There's no air to make an impulse, a push. Even if there was air, 50 MT is not nearly enough to damage large objects. Nukes aren't that powerful. They look spectacular, though.