A thought on killing planets

[Spoo]

Is it really realistic that a light cruiser armed with a few uranium cannons could kill the entire population of a planet? Perhaps a fleet of Dreadnaughts with planetary napalm could, but with the exception of such large scale weapons, it should require an actual invasion with troops to conquer a planet. I think that only certain weapons should be able to kill population, but that the damage dealt by these weapons should be increased.