History
Grått was not located in either the Horsehead Nebula or the Crab Nebula. It exhibited a breathable atmosphere and witnessed both rain and temperate weather. It was described as a "dwarf planet" meaning it probably had very short days.
At some point, an Empathivore invaded and killed several Gråttites. To keep the beast under control, the Gråttites had to start hiding their emotions. At this point, they built the Whispering Gallery.
Several generations later, the Tenth Doctor and Martha Jones came to the planet and defeated the Empathivore, allowing the Gråttites to live in peace once more.
The Doctor's companion, Grayla, hailed from this planet. A large statue of her was erected after the defeat of the Empathivore. (IDW: The Whispering Gallery)