From The Askelline Incursion:
Far worse occurred at Menoetius-Delta. The Space Hulk that emerged in that system did so not at its outer edges, but far in-system. Menoetius-Delta was host to a subsistence-level society that had never truly taken its place in theSector and, thanks to the Space Hulk, never would. Three days after it was detected, the gigantic conglomeration of metal and rock smashed into Menoetius-Delta, triggering an extinction-level event that rendered the surface nigh uninhabitable to Humanity. It was later estimated that approximately fifty million souls went to the Emperor’s Side when the Space Hulk collided with Menoetius-Delta, and the same number perished in the years that followed as its ecology collapsed. No mission was ever launched to evacuate survivors, and it is likely their descendants live there still, eking out a miserable and short life beneath the churning black clouds, the light of the star of Menoetius merely a myth passed down through the generations.