Valhalla

Valhalla was originally a verdent Paradise World, home to the Imperial Guard regiment Valhallan Ice Warriors. No records survive of its colonisation, but legends recall a world ripe for conquest. Unfortunatly, Valhalla was destined for something else. It was hit by a gigantic comet. The defence lasers surrounding the planet blasted the comet, but only succeeded in breaking it up. Later, it was found that the comet was made of almost pure iron, explaining why the lasers were so ineffective. The comet impacted in the vast ocean spanning most of the planet but a mile-wide fragment impacted the northern continent, creating vast plumes of dust which proceeded to cover the planet in a blanket of dirt. Also, the planet's orbit was changed, moving it farther away from its star. This change in the amount of warmth and light altered the planets ecosystem, changing the planet to an icy wasteland.