Sometime in the next several weeks, the Chinese space lab Tiangong-1 will re-enter the atmosphere. The uncertainty of just when this 8.5-ton spacecraft will re-enter reflects the remarkable possibility that this reentry is uncontrolled. And just as it is unclear when it will re-enter, it is also unclear where it will do so. Although the likelihood is high that it will be over water (if only because most of the Earth’s surface is covered in it), that will be small comfort should it come down over a populated area.