If they are so much as inconvenienced by our probes, they are not a greater power but bumbling roboticists like us.

1 gram at an appreciable amount of c is about as much energy as a nuke. Getting hit by a swarm of these while on a Sunday drive would fuck you up, no matter how powerful you are.

The real reason there isn’t a moon colony? Person gets fired and loses their shit, starts tossing 1-2 km sized rocks down the gravity well and … we all die.

Throwing shit in space is a sure fire way to piss off any species.

It would take an insane amount of energy to throw that rock.

But you only need one. Maybe two for good measure

Same with a nuke or an engineered pathogen. Throwing rocks from the Moon is less practical though, people would see you setting up the universe's biggest launch pad or railgun for years. It would be the least stealthy, most telegraphed apocalypse possible.

It only takes a 50-meter (radius) rock to destroy a city, a 240-meter rock to destroy an entire region, and a 4 km rock to destroy the planet.

So, I guess it depends on what you want to accomplish, whether they see it coming or not.

"Only". Those are huge! Especially when you consider the city you have to build around them to launch the damn things.

The required delta-v isn't all that much from the moon, and it's more about the mass and speed than the actual shape of the rock.

To throw a 100 meter rock that would wipe out NY city (and then some), we could do that with modern technology... assuming the rocket never had to slow down.