For two weeks in August, a multimillion-dollar search from air, land and sea sought to solve the 80-year mystery of Amelia Earhart’s disappearance.

Robert Ballard, the ocean explorer famous for locating the wreck of the Titanic, led a team aboard the resesearch vessel Nautilus that discovered two hats in the depths. It found debris from an old shipwreck. It even spotted a soda can. What it did not find was a single piece of the Lockheed Electra airplane flown in 1937 by Amelia Earhart and Fred Noonan, which vanished during their doomed voyage around the world.

Dr. Ballard and his crew don’t consider it a failure. For one thing, he says, they know where the plane isn’t. And in the process, they may have dispensed with one clue that has driven years of speculation, while a team of collaborating archaeologists potentially turned up more hints at the aviator’s fate.

“This plane exists,” Dr. Ballard said. “It’s not the Loch Ness monster, and it’s going to be found.”