All seven on board were killed, including the first schoolteacher bound for space, Christa McAuliffe.
The remnant is more than 4.5m by 4.5m; it’s likely bigger because part of it is covered with sand. Because of the presence of square thermal tiles, it’s believed to be from the shuttle’s belly, officials said.
The fragment remains on the ocean floor just off the Florida coast near Cape Canaveral, as Nasa determines the next step.
It remains the property of the US government.
Ciannilli said the families of all seven Challenger crew members had been notified.
A History Channel documentary detailing the discovery airs in the US on November 22.