It collided in between July 16 and July 22, 1994.
-Wrong, this is what it said:
"Following up on a tip by an amateur astronomer, Anthony Wesley of Australia, that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT (6 a.m. and noon EDT) scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using NASA's Infrared Telescope Facility at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact."