Torino scale

A 0-to-10 impact hazard rating designed to stop scary numbers being misread.

The Torino scale combines collision probability and kinetic energy into one integer with a colour band, specifically so the public conversation about an impact risk is not conducted in probabilities. Zero is no hazard, and essentially every object ever catalogued has ended at zero once its orbit was pinned down with more observations. Apophis briefly reached 4 in 2004, the highest ever assigned, and was later ruled out entirely for the next century. The scale is deliberately coarse and deliberately temporary. Almost every object that scores above zero does so because its orbit is barely constrained — a wide uncertainty ellipse that happens to include the Earth — and a fortnight of further observation shrinks the ellipse and drops the score. A number that goes up and then to zero is the system working, not a near miss.