The ancient Egyptian pyramids were built more than 4,000 years ago, and modern scientists have been studying them for two centuries. But as a new research project illustrates, these iconic tombs are still teeming with mysteries.

Using infrared thermal scanners, an international team of investigators has identified major anomalies at several of Egypt's most famous pyramids, including a particularly "impressive" heat spot on the Great Pyramid of Giza (aka the Pyramid of Khufu).

Launched on Oct. 25, the #ScanPyramids project focuses on Khufu, Khafre, the Bent and the Red pyramids. It combines several non-invasive and non-destructive scanning techniques "to detect the presence of any unknown internal structures and cavities in ancient monuments," according to a press release issued by Egypt's Ministry of Antiquities and the Heritage Innovation Preservation (HIP) Institute.

Researchers performed the thermal scans at sunrise, when sunlight heats up the pyramids, and at sunset, when the structures begin cooling down again. If an object is solid — i.e., built with blocks of the same material that emit heat at similar rates — this shouldn't reveal any major temperature differences. On the other hand, if there are any quirks in the structure — like varying materials or hidden cavities — some parts will heat up or cool down more quickly than others.

Egypt pyramids infrared scanInfrared scanners are just part of the effort to unveil secrets in Egypt's pyramids. (Photo: Philippe Bourseiller/HIP)

"At the end of the first mission of #ScanPyramids, the teams ... have concluded the existence of several thermal anomalies that were observed on all monuments during the heating up or the cooling down phases," the Ministry of Antiquities says in a statement. "Among the various identified thermal anomalies, the team observed a particularly impressive one located on the eastern side of the Khufu Pyramid at ground level. It is interesting to observe that while sometimes temperature differences of 0.1 to 0.5 degrees are detected between two adjacent stones from limestone of different qualities, the #ScanPyramids infrared team has detected in this zone an area of few blocks having up to 6 degrees gap with neighboring blocks!"

The scans show that the pyramid's first row of limestone blocks all have roughly the same temperature, according to Antiquities Minister Mamdouh Eldamaty, aside from three that are also "different in formation" from other blocks. And while inspecting the ground in front of the pyramid's eastern side, Eldamaty says the researchers also found "there is something like a small passage leading up to the pyramid ground, reaching an area with a different temperature."

Egypt pyramids infrared scanA thermal anomaly on these blocks has raised new questions about the ancient pyramids. (Photo: Philippe Bourseiller/HIP)

"What could be behind it?" Eldamaty asked rhetorically during a press conference this week, urging Egyptologists around the world to help brainstorm theories.

No one is sure yet what the anomalies mean — they may hint at gaps or fissures in the walls, or possibly hidden passageways or chambers. (But, despite the claims of U.S. Republican presidential candidate Ben Carson, they're not seen as evidence of the pyramids having been used to store grain.)

This teaser video, released by the Egyptian Ministry of Antiquities and the Paris-based HIP Institute, offers more detail about the project:

"I don't know yet what could lay behind such blocks or what these anomalies could be, but it will surely lead to major discoveries," Eldamaty tells Egypt's Ahram Online. "I have several hypotheses in mind, though I cannot reveal them before conducting further research and study."

More information should be revealed in coming weeks, Eldamaty adds, although the overall project is scheduled to continue through 2016. The researchers will soon use muon radiography — a technology that has been famously used in Japan, both to scan active volcanoes and to look inside reactors at the tsunami-stricken Fukushima nuclear power plant. The research will also involve 3D modeling and simulations of the pyramids via lasers and drones, as well as long-term infrared scans.

"In the longer term, given the archaeological wealth of Egypt, we imagine applying these techniques to other monuments," Cairo University professor and project coordinator Hany Helal says in a statement. "Either to restore or to discover them. If these technologies are effective, they can even be implemented in other countries."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.