The divers for a TV documentary plunged deep into the Atlantic Ocean on Feb. 26, hoping to find a search-and-rescue aircraft that had been lost since 1945. Mike Barnette dived farther and farther into murky waters that obscured his vision, as if he were swirling inside a glass of Guinness, until his fingers touched a flat metal object.
They couldn’t tell what it was, so the crew returned to the site on May 5, and there in the sand, with fish swimming above it, was a piece of history emblematic of one of the country’s darkest days: a large section of the space shuttle Challenger, which had exploded on the morning of Jan. 28, 1986, to the horror of people watching the launch on TV across the country.
The accident, one of the worst in the history of the American space program, killed all seven crew members on board, stunning a devastated NASA program, which spent weeks searching the ocean for debris. At least one large piece had apparently remained lost for decades.
“The tragedy of that, and remembering watching it as a kid — it’s a mix of emotions to literally, literally, touch history,” Mr. Barnette, 51, said in an interview on Thursday.
“We weren’t expecting it because we were under the assumption that all these pieces were recovered by NASA for their investigation,” he added.
Mr. Barnette, a marine biologist of St. Petersburg, Fla., and his diving partner, Jimmy Gadomski, spent parts of this year searching the ocean for World War II-era aircraft for a documentary that will air on The History Channel, “The Bermuda Triangle: Into Cursed Waters.” Fishermen had informed them of places to search, Mr. Barnette said, because fish typically seek structures underwater that offer protection, and those structures are sometimes man-made.
NASA confirmed the divers’ discovery in a statement on Thursday, saying that officials had reviewed the footage and determined that the artifact was from the Challenger. The space agency is still investigating what part of the shuttle the piece belonged to, but Mr. Barnette said that because of its red pads, it appeared that the object is “a significant portion” of the orbiter’s underside.
Video and photos of the piece show a flat object measuring larger than 15 feet by 15 feet and covered with dark squares that have been partly tattered and coated with sand.
“For millions around the globe, myself included, Jan. 28, 1986, still feels like yesterday,” Bill Nelson, the administrator of NASA, said in a statement. “This discovery gives us an opportunity to pause once again, to uplift the legacies of the seven pioneers we lost, and to reflect on how this tragedy changed us.”
The crew members who were killed were Lt. Col. Ellison S. Onizuka of the Air Force; the pilot, Cmdr. Michael J. Smith of the Navy; Christa McAuliffe, a high school teacher; the mission commander, Francis R. Scobee; Gregory B. Jarvis; Dr. Ronald E. McNair, the country’s second Black astronaut; and Dr. Judith A. Resnik, a biomedical engineer.
Seventeen years after the Challenger explosion, Columbia, another shuttle, was re-entering Earth’s atmosphere on Feb. 1, 2003, when it broke up, killing its seven crew members and sending debris across Texas.
Ms. McAuliffe’s inclusion in the Challenger mission had stirred excitement among the country’s students and educators, with thousands of them, including Mr. Barnette, watching the launch, entranced by the possibility of a teacher in space.
“I remember the day, I remember where I was,” Mr. Barnette said. “It’s conjured all those emotions and what the whole nation went through.”
Mr. Barnette said he could not disclose where exactly the discovery was made because officials do not want amateur divers touching and damaging the piece. But Mr. Barnette and NASA said it was located off the Florida coast near Cape Canaveral, northwest of the area known as the Bermuda Triangle. The piece, which is the government’s property, will remain there until NASA decides what to do next.
The agency said that it was “considering what additional actions it may take regarding the artifact that will properly honor the legacy of Challenger’s fallen astronauts and the families who loved them.”
As the divers resurfaced to their boat in May, Mr. Barnette recalled, crew members were stunned.
“We were just amazed,” he said.
As the ocean current gently rocked their boat, Mr. Barnette explained to the documentary crew, fixed with cameras and microphones, what he had seen underwater: The dark squares, the metal. There in the water, he told them, was a flat object covered with sand that had, clearly, once belonged to a spacecraft.
“We basically tore off a scar,” he said, “that was 36 years old.”