Robert Ballard is the finder of important lost things.

In 1985 , he discovered the Titanic scattered beneath the Atlantic Ocean. He and his team also located the giant Nazi battleship Bismarck and, more recently, 18 shipwrecks in the Black Sea.

Dr. Ballard has always wanted to find the remains of the plane Amelia Earhart was flying when she disappeared in 1937. But he feared the hunt would be yet another in a long line of futile searches.

“You have it in a holding pattern in your head,” said Dr. Ballard, founder of the Ocean Exploration Trust. “You’re still saying, ‘No, no, it’s too big a search area.’”

Then, a few years ago, another group of explorers found clues so compelling that Dr. Ballard changed his mind. Now, not only is he certain he knows where the plane is, he has set course for a remote atoll in the Pacific island nation of Kiribati to recover it.