Today Google celebrates the 115th birthday of aviatrix
© UnknownAmelia Earhart
Amelia Earhart -- and one of the great unsolved 20th-century mysteries.

Sorry, Amelia, no birthday present this year. But it's not been for a lack of trying.

Throughout the years there have been a number of search attempts to find Earhart or wreckage of her plane. Now 75 years after she vanished in her Lockheed Model 10 Electra over the Pacific Ocean, the most recent hope of finding evidence of Earhart's plane is fading.

Discovery News reported last week that a $2.2 million expedition by The International Group for Historic Aircraft Recovery (TIGHAR) came to an end due to the challenges of exploring a steep, underwater coral cliff.

You remember, a couple of months ago, Secretary of State Hillary Clinton held a press conference, and gave an boost to the credibility to the TIGHAR hunt for Earhart's plane.

TIGHAR researchers believed that when Earhart and her navigator Fred Noonan went missing July 2, 1937, they made an emergency landing on a reef near the uninhabited island Nikumaroro.

"Everything has pointed to the airplane having gone over the edge of that reef in a particular spot and the wreckage ought to be right down there," Rick Gillespie, the founder and executive director of TIGHAR, told The Associated Press in early July. There were reports of a 1937 British photo that showed the wreckage of the plane in the background.

"We're going to search where it 'should be,'" he said. "And maybe it's there, maybe it's not. And there's no way to know unless you go and look."

But last week, TIGHAR called off the expedition because of the difficulty of searching the reef. The slope of the reef was quite steep, and it was filled with nooks, crannies, caves, and crevices. One researcher at TIGHAR questioned the feasibility of the search.

In addition, two "targets" -- which they thought could have been part of the wreckage of Earhart's plane -- turned out to be a large coral boulder and a piece of the keel from The Norwich City, a well-known ship wreck.

"Given what we now know about this place, is it reasonable to think that an airplane which sank here 75 years ago is findable?" asked Patricia Thrasher, TIGHAR's president, in an interview with Discovery News. "It would be easy to go over and over and over the same territory for weeks and still not really cover it all." And added Thrasher: "The aircraft could have floated away, as well."

The TIGHAR search, funded in part by Discovery Channel and FedEx, began on July 3, and was scheduled to last about 26 days. Since 1989, TIGHAR has conducted 10 expeditions near Nikumaroro Island, which is part of the Pacific nation of Kiribati.

TIGHAR researchers say that significant finds on Nikumaroro lead them to continue to believe Earhart and Noonan may have survived as castaways there for some time. They found a zipper from the 1930s, a cosmetic bottle -- possibly for anti-freckle cream -- and human bone fragments.

Other researchers who have been involved in searching for clues to Earhart's disappearance say TIGHAR has been looking in the wrong place. Earhart, who was attempting to become the first woman to circumnavigate the globe, had planned to stop and refuel on Howland Island. Some say she wouldn't have had enough fuel to make it to Nikumaroro, which is about 400 miles southeast of Howland Island.

They also point to Earhart's last radio transmission; it is thought that when Earhart made her last radio call she was within 75 miles of Howland Island, though the surrounding area has been comprehensively searched.

TIGHAR points to other radio signals they say came from Nikumaroro; radio signals that at the time were dismissed as a hoax and then forgotten.

"Radio distress calls believed to have been sent from the missing plane dominated the headlines and drove much of the US Coast Guard and Navy search," Gillespie told Discovery News. "When the search failed, all of the reported post-loss radio signals were categorically dismissed as bogus and have been largely ignored ever since."

Other artifacts found throughout the years point to long-term habitation on the island. Broken pieces of glass could have been used as cutting or scraping tools, and large numbers of fish and bird bones near ash and charcoal deposits suggest someone was surviving on the island.

Researchers also found a pocket knife, part of a man's shoe, and part of a woman's shoe, all thought to be clues to Earhart's disappearance.

Other rumors have included a theory that Earhart was really a spy for the US, and was captured by the Japanese.

Baring hard evidence, for now it seems, Earhart's disappearance will remain as mysterious as ever.