Complex sentence: Had this object hit Earth, it would probably have detonated high in the atmosphere, and might have produced a blast measured in hundreds of kilotons of TNT, but may not have produced any ground level effect.
Split into simpler sentences: Had this object hit Earth, it would probably have detonated high in the atmosphere. It might have produced a blast measured in hundreds of kilotons of TNT, but may not have produced any ground level effect.