03/11/2017 1:39 AM AEDT | Updated 03/11/2017 8:26 PM AEDT

Mysterious Void Found In Egypt's Great Pyramid Of Giza

'We open the question... what could it be?'

A huge void has been discovered in the Great Pyramid of Giza by scientists using an imaging method based on cosmic rays.

Experts announced the find on Thursday but have admitted they don’t know what the cavity inside the pyramid, built as a monumental tomb around 2560BC, is for.

To see inside the pyramid, the scientists used an imaging technique called muon tomography that tracks particles that bombard Earth at close to the speed of light and penetrate deeply into solid objects.

Scan Pyramids Mission
Experts have admitted they don't know what the giant void in the Great Pyramid of Giza is for 

They said the newly discovered internal structure was at least 100 feet long, and located above a hallway measuring about 155 feet long called the Grand Gallery, one of a series of passageways and chambers inside the immense pyramid. The researchers said it constitutes the first major inner structure found in the Great Pyramid since the 19th century.

“What we are sure about is that this big void is there, that it is impressive, that it was not expected by, as far as I know, any kind of theory,” said Mehdi Tayoubi, president and co-founder of the HIP Institute in France, one of the leaders of the study published in the journal Nature.

Scan Pyramids Mission
The void was discovered using cosmic particle detectors 

“We open the question to Egyptologists and archaeologists: what could it be?” added Hany Helal of Cairo University.

The Great Pyramid, looming alongside other large pyramids on the outskirts of Giza, is the last of the Seven Wonders of the Ancient World still standing.

It soars to a height of 479 feet, the tallest structure built by humankind until the Eiffel Tower in Paris in 1889, and boasts a base measuring 754 feet.

Scan Pyramids Mission
3D scans with lasers and drones were also used as part of the investigation 

It was constructed during the reign of the Pharaoh Khufu, or Cheops.

Zahi Hawass, a previous Egyptian antiquities minister, believes the pyramid still contains the tomb of Khufu and that it is unplundered. 

DEA / G. DAGLI ORTI via Getty Images
An ivory statuette of Khufu 

Ahead of the discovery, he told The Times: “I really believe that [Khufu’s] chamber is not discovered yet and all the three chambers were just to deceive the thieves, and the treasures of Khufu [are] still hidden inside the Great Pyramid.” 

The findings come from a project called Scan Pyramids that relies on non-invasive scanning methods to probe the internal structure of the pyramids of ancient Egypt’s glorious Old Kingdom period and understand how they were built.

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The Great Pyramid soars to a height of 479 feet

“We are not doing this mission in order to find hidden cavities,” Helal said.

Muon particles originate from interactions between cosmic rays from space and atoms of Earth’s upper atmosphere. The particles can penetrate hundreds of yards into stone before being absorbed. Placing detectors inside a pyramid can discern cavities within a solid structure.

Scan Pyramids Mission
Infrared thermography readings of the structure were also taken 
Scan Pyramids Mission