The Hazard Flag Isn't About Distance

A handful of asteroids slide past Earth every day, and a few wear an official red flag: potentially hazardous. The intuition is obvious — those must be the ones cutting it close. They're not. The flag is a fixed property of a rock's size and orbit, decided once and for all, with nothing to say about today's miss. Plot a month of them and the label and the closeness point in perpendicular directions. Live from NASA.

How this was made. Every near-Earth object with a close approach in the — days ending —, pulled from NASA's NeoWs feed (the Center for Near-Earth Object Studies, JPL). Each rock is placed by its miss distance (horizontal, in lunar distances — 1 LD = 384,400 km) and its estimated diameter (vertical; the bar is NASA's own min–max range, since size is inferred from brightness and an unknown albedo — a factor of ~2 either way). The “potentially hazardous” flag is set by JPL from two things only: the orbit's minimum distance to Earth's (MOID < 0.05 AU) and the rock being big enough (absolute magnitude H ≤ 22, ≈140 m). Neither is today's pass. GREEN: all — flagged rocks sit above the 140 m floor — the label is a size cut. FAULT: predict the flag from closeness instead — call the — nearest passes “hazardous” — and it recovers only — of the real ones. Baked on wake; the sky is still moving.

“Potentially Hazardous” Is Not About How Close It Comes