Actually, we are not talking about a large asteroid, but a planetoid like Ceres.

● Discovery Channel – Miracle Planet – Large Asteroid Impact Simulation (2008). Earth was born as a result of repeated asteroid collisions, the moon was created by a single giant impact event. Then, Earth's size attracted huge meteorites, which slammed into it, causing super-high-temperature rock vapour to cover the entire surface and evaporate all ocean water.