9969 Braille

9969 Braille is one of the smallest asteroids ever visited by a spacecraft, and its claim to fame is a flyby that almost did not work. On 29 July 1999, NASA’s Deep Space 1 — a technology-demonstration probe built to test an ion engine and autonomous navigation — swept past Braille at a distance of just 26 kilometres, then the closest approach ever attempted to an asteroid. A tracking glitch in the final hours meant the camera missed the moment of closest pass, and the best images were taken about fifteen minutes later from some 14,000 kilometres away.

Braille is a small, elongated body measuring roughly 2.1 kilometres along its longest axis. It is a rare Q-type asteroid, composed mostly of olivine and pyroxene, and it follows an eccentric Mars-crossing orbit. Early ground-based spectra had hinted that Braille might be a V-type fragment chipped from the giant asteroid 4 Vesta, but the closer measurements pointed instead to a Q-type classification, leaving its exact kinship uncertain. It is also an unusually slow rotator, turning only once every nine days or so.

Discovered in 1992 by Eleanor Helin and Kenneth Lawrence at Palomar Observatory, the asteroid was later named after Louis Braille, the inventor of the raised-dot reading system used by blind people. Modest in size and dimly understood, Braille still earned its place in history as the first asteroid that Deep Space 1 went out of its way to meet.