Amelia Earhart and her plane have been lost since 1937, but researchers will look again this summer. (Associated Press)

This summer, scientists will set out to try to solve one of the great mysteries of the past 75 years: What happened to Amelia Earhart?

Earhart gained worldwide fame when she became the first woman to fly a plane alone across the Atlantic Ocean in 1932, five years after Charles Lindbergh became the first person to do this.

But in July 1937, while trying to become the first woman to fly around the world, Earhart’s plane disappeared over the Pacific Ocean. Despite radio transmissions from her in the hour before the plane disappeared and many searches, no sign of her, her navigator who was flying with her or her plane has ever been found.

Now, 75 years after she vanished, scientists are launching the most massive search ever to find out what happened to the 39-year-old flier.

Among those who are hoping to get answers is Secretary of State Hillary Clinton, who called Earhart one of the “fearless optimists” of the 20th century. In wishing the scientists well in their search, she said, “Even if you do not find what you seek, there is great honor and possibility in the search itself.”

The search is being conducted by the International Group for Historic Aircraft Recovery, also known as TIGHAR. The group’s leader, Ric Gillespie, said the search is based on a 1937 photo of what looks like the underside of a Lockheed Electra airplane, like the one Earhart was flying, coming out of a reef. The photo was taken near Nikumaroro Island, about 2,500 miles northeast of New Zealand.

In July, researchers will head to Nikumaroro aboard a research ship that can map underwater using small robotic submarines.

Gillespie isn’t sure that they’ll find what has been lost for 75 years. “The only thing we can do is make a best effort to go and search and look and see what we can find. And it’s the searching that’s important. It’s the trying that’s important,” he said.

Oceanographer Robert Ballard, who discovered the Titanic in 1985 and who studied the latest Earhart project, said Gillespie’s team seems to have narrowed the “box” in which Earhart’s wreckage might be found.

“He’s got a reasonable box now, and he’s certainly got all the technology to do it. So all I can say is I wish him a fair wind and a following sea — and a little luck.”

— Staff and wire reports