So, something that pleases my brain:
I found an ancient blog where a rocket scientist after watching ID4 did some math and determined that the entire stockpile of nuclear weapons available in the whole world at the time would maybe be sufficient to mission-kill a single one of the 15-mile-wide flying saucers, even with its energy shields offline.
To put it in perspective, a single solid structure 15 miles in diameter and maybe half a mile tall would probably come close to outmassing all the buildings in the entire world combined. And that’s assuming it was built like a modern submarine or aircraft carrier, it’ll be worse if it’s made of neutronium or some hyperdense alien metal, as the mothership having a tenth the mass of Earth’s moon would imply.
Speaking of that mothership that stayed in orbit, and is 550 goddamn kilometers long, you’d need a proper planet-killer unless they were really bad at having internal compartmentalization to contain explosions.
White Paper 1996-3: Rocket Scientist's Reaction to Independence Day
For the Star Wars fans, that would probably be relatively similar for the 5km-19km long super star destroyer, and the 120-900km diameter (depending on who you ask) Death Star.