An expedition to a remote Pacific island hoping to solve the decades-old mystery of aviator Amelia Earhart's disappearance has ended without a breakthrough. Researchers confirmed that an object previously suspected to be her missing aircraft was most likely a cluster of washed-up trees.

"Unfortunately, we weren't able to find that smoking gun," said Steve Schultz of Purdue University, speaking on the atoll of Nikumaroro, located roughly halfway between Australia and Hawaii.

Earhart and her navigator Fred Noonan vanished in 1937 during an attempt to circumnavigate the globe at the equator. Their disappearance triggered one of the largest air and sea searches in history. Nearly 90 years later, the mystery remains unsolved.

Nikumaroro, part of the Pacific archipelago nation of Kiribati, has long been considered a leading candidate for where the pair may have crash-landed. Previous visits to the uninhabited atoll have uncovered signs of a castaway camp, a 1930s-era woman's shoe, and other artefacts attributed to Earhart, including glass from a cosmetics freckle cream jar.

The latest mission was prompted by satellite images taken in 2020 showing an elongated white object lying in the shallows near a sandy outcrop called the Taraia Peninsula. Some experienced Earhart researchers quickly identified it as a fallen tree. However, Richard Pettigrew, who heads the nonprofit Archaeological Legacy Institute, found additional imagery, including aerial video, that he believed showed a metallic glint in the water.

A 17-person expedition subsequently made a multi-day voyage by ship to investigate. After delays caused by bad weather, the team passed through the coral-encircled atoll and set up camp to conduct four days of research, including metal detecting. The crew was forced to sleep offshore, partly due to large land-dwelling coconut crabs, known locally as robber crabs for their inquisitive behaviour when searching for food.

By Monday, Purdue University confirmed in a statement that the object was "likely a collection of large trees deposited along the peninsula's sandspit."

The university also explained the metallic appearance that had fuelled speculation. "The fragment's reflective surface, long associated with the idea that the object was a metallic substance, was due to its carbonate veneer. Other items found by the team were similarly coated with a shiny concretized amalgam of coral sand," the statement read.

Purdue University had partially sponsored the trip. Earhart once taught and mentored young female pilots at the Indiana institution, which also helped fund her modified Lockheed Electra 10-E, known as her flying laboratory.

"While we know this is disappointing to many, including us, this mission adds a new chapter in the quest to find the ultimate answer to the mystery of what happened to Earhart during her attempt to circumnavigate the globe nearly nine decades ago," the university said.

The failed expedition adds to a growing list of dismissed theories surrounding Earhart's fate. These have included claims that she was captured by Japanese forces and that she survived the disappearance and lived under an assumed identity. Earhart was the first woman to complete a nonstop solo transatlantic flight.