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: 
Let's turn our thinking around. Instead of asking, "how could alien attacks send humanity into a diaspora?" we can ask, "what would aliens do if they *wanted* to scatter humanity like this?" Say, for instance, the aliens don't want to permanently ruin the worlds that the humans have colonized (because those worlds could be used by the aliens down the line), but they want to keep the humans off of them for a while.

I've come up with a machine that could do the trick. It's a massive, self-powered vehicle the aliens have developed, which burrows into a world's surface once it lands on the least-defended area of the planet. Once deep in the planet's mantle, it sends out extremely powerful EM pulses constantly, which disrupt electronics all over the planet but dissipate harmlessly at larger ranges.

Any human habitats on the planet will immediately lose life support and become uninhabitable, forcing an evacuation or worse. The humans can't just move to another location on the planet, because these EM pulses don't stop. Perhaps with some ingenuity, they could build Faraday-cage-enclosed habitats, but it would be dangerous setting that up in the first place while that machine is still running, given that all of humanity's habitat-building tools are themselves electronic.

But couldn't the humans just destroy the device, you ask? Well, sure, maybe they could get a high-power enough laser from far away enough in space to vaporize a hole all the way down and destroy it, or something like that. But that takes a lot of time and a lot of resources. Maybe some governments were working on just such a solution, and the aliens eradicated them before they could finish.

These planet-wide EM-producing digging machines are, of course, very expensive for the aliens as well, so it makes sense that they only sent them against the main human settlements, and have spared the scattered outposts.
**Rocks**

Simply put you throw rocks at stuff you don't like.

Fortunately our solar system is *full* of rocks just waiting around doing nothing, so we just grab a few (OK, more than a few) and direct them gently at the source of the problems (any inhabitable place) and wait for nature (and gravity) to takes it course.

In the due course of time you can not only wipe out all life, but ensure it won't be producing or supporting any life for millions of years.

Everyone wins.