Stellaluna

The planet is a frozen rock, drifting alone through space. Once, it was a star of great beauty and power, eons ago. Then, it became a white dwarf, puffing off a stellar nebula that can be seen to this day.

Now, it has drifted away from the gossamer deathshroud it built for itself, and the cold relic has entered orbit around an unassuming Sol-like star, itself alone in its lonely orbit around the galactic core.

Stellaluna, the moon-that-was-a-sun, has evolved into a gigantic diamondlike crystal over its long slow death, and it sparkles and gleams in the heavens like a jewel. The world is worthless, for carbon and diamonds are trivial to come by in the 40th Millennium, but the center of the starheart glows of its own accord.

Though Oestalan is at the very edge of the galaxy near the Halo Stars, Stellaluna resonates with the Astronomicon, beaming the Emperor's grace into the local area like a distant reflection of his light.

This, then, is the lighthouse of Oestalan, ceaselessly resonating with the Emperor's grace. The Crusade must secure a hold of the system and its priceless relic, for a Chaos warlord has been given a quest, to find the diamond, protected as it is in the vastness and sluggish Warp currents of the Halo Zone, and shatter a crystal the size of Terra itself.

Legend has it that if Stellaluna is broken asunder, the Great Storm will return with a terrible vengeance, and Oestalan will be lost eternally.