WE CAN USE THEM TO DELIVER WATER TO MARS, TOO: ‘Devil Comet’ contains ‘strongest evidence yet’ that comets delivered water to Earth.

Of course, as Martyn Fogg demonstrated in his magisterial Terraforming: Engineering Planetary Environments, you need a fair number of comets, and bigger isn’t necessarily better. Past a certain size, the impact blows most of the water back into space. Although maybe you could slow them down before impact somehow . . .