Question: For the Universe I am creating humanity has devolved into groups of scattered tribes. This is due to the fact that we ran afoul of a *really* nasty alien race, who decided to leave us homeless. A coalition of races had banded together to fight this menace, but mankind ended up with the short end of the stick. It is the Great *Diaspora*, and we are only hanging on by our fingernails.

The problem I am having is how to thoroughly destroy or at the very least render uninhabitable the places Man once called home. If it were only Earth it would be a simple enough matter, but by the time the attack takes place he *also* has colonies on Luna, Mars, Ceres, Callisto, and Titan. How can I muck them up badly enough that we have to now seek a Promised Land elsewhere?

Ceres I figure is small enough it could just be reduced to rubble, but what about Luna? If you destroy the colony there, what would prevent them from setting up new ones a few hundred miles away? 

At the moment all I can think of is a "Gray Goo" weapon, short of blasting multiple planets and moons to smithereens. I am hoping there is another option out there I haven't considered.

EDIT: I'd like to hold onto the Sun. You know, sentimental reasons. :)

Answer: 
Self Replicating Drones

The enemy race drops a 3d printer/mobile factory on an asteroid. It starts building more of itself, and creates swarms of drones. It keeps doing this. Eventually there are so many drones you can't have a civilization anymore, either because enough of the mass of the solar system is converted into drones, or you give up and leave and the factories go into hibernation mode.
#### Spheres of cobalt 59 orbiting the sun

The alien placed a lot of spheres of cobalt 59 in orbit around the Sun. The orbits are so eccentric that at the perihelion they graze the Sun surface and the heat ablates a layer of the surface, then the solar radiation turns it into cobalt 60. Now you have a very radioactive solar wind and, since those atoms were not in the plasma, many of them are not ionised therefore they can pass through the barrier of the Earth magnetic field.