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: 
**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.
Make other options more attractive.
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The only easy place to build inside our solar system is earth. Everything else kinda sucks. We could build a colony on Mars or some of the moons of Jupiter but it's pretty far from ideal. The only reason we consider it at all is because there aren't any other options we can reach.

If this event got humanity in contact with other aliens, and provided FTL technology, then it may simply be that we don't return to our old home because Earth has been made uninhabitable in some way and ***there are so many better options now.***

Turns out the universe has loads of Earth-style planets with no intelligent race living on them so there's simply no reason to go build a domed Mars colony or deal with hostile atmospheres or cold climates. Just pick one of thousands of known, hospitable, unclaimed, Earth-like planets and starting the colony is far easier and cheaper.