Physicists are closing in on new techniques to put ancient archaeological sites through a cosmic "CT scan" to look for hidden chambers, using showers of subatomic particles known as muons.
The idea was first put to the test in an Egyptian pyramid four decades ago - but researchers saw no surprises in that experiment. Now, scientists are hoping to enlist a new generation of muon detectors to solve long-running mysteries of the Maya.
Roy Schwitters, a physicist at the University of Texas in Austin, provided an update on his team's plans for archaeological scans on Sunday at the annual New Horizons in Science briefing, presented in Spokane, Wash., by the Council for the Advancement of Science Writing. You can click through an early version of his PDF presentation here.
Schwitters and his colleagues are focusing on mounds in the jungles of Belize that are thought to cover the remains of structures dating back to the Classic Maya era (A.D. 250-900) or even earlier.
"There is good reason to believe they contain rooms and chambers ... that have been likely undisturbed since the time of the Maya," Schwitters told the audience here in Spokane. But you can't dig up the sites willy-nilly looking for lost tombs, and non-invasive techniques such as ground-penetrating radar, electrical probes or seismic sampling "just can't work in this medium," he told me during a Q&A.
This is where muons just might ride to the rescue. When cosmic rays hit Earth's atmosphere, they spark showers of muons and neutrinos that interact only weakly with intervening matter. The neutrinos are almost unaffected as they pass through our planet, but different densities of matter deflect the muons to different degrees. Thus, it's possible to build muon detectors to determine what those subatomic particles have passed through.
"It's just perfect for what we want to do," Schwitters said.
Over the course of several months, one detector can build up a picture showing the "shadows" of surrounding objects - like buildings on the Austin campus, for example. If you put in multiple detectors, or move a single detector to multiple locations, you can create a 3-D picture of the site using muons, in the same way that CT scans produce a 3-D picture of your body using X-rays.
"It literally is like tomography in the medical sense," Schwitters explained.
You do have to bury the detectors in the ground surrounding the site you want to survey - and that could pose a problem if the site is as culturally important as the places Schwitters and his team are targeting.
They started out building a prototype cylindrical detector that was about 5 feet (1.5 meters) wide and 15 feet (4.5 meters) tall. The device had to be constructed like an airplane fuselage, then filled with specially designed swirls of plastic and fiber-optic scintillators. "It's the biggest thing we could imagine getting into Belize," Schwitters said.
Since then, the Texas team has shrunk the design for the device into something that would be "about the size of a water heater," weighing 200 pounds (90 kilograms) rather than a ton, Schwitters said. Those detectors are now being built and tested, and the team's first archaeological scans in Belize could begin in the spring of 2009.
The smaller devices wouldn't be nearly as intrusive as the one-ton detector. Schwitters said a half-dozen of them could be buried at various spots around the edges of a target site, about 10 to 15 feet deep (as opposed to about 30 feet deep for the bigger version).
Schwitters said computer simulations indicate that the mini-muon detectors could spot the telltale signs of a buried chamber the size of a hotel ballroom - but he admitted that the system would have to be put through some test runs before beginning the Belize survey. "To convince people you can really do this, you need to do the voids," he said.
Meanwhile, other scientists are working on a more straightforward muon detection system to survey Mexico's Pyramid of the Sun - a structure that dates back to A.D. 200, before the age of the Aztecs. Those researchers, led by Arturo Menchaca-Rocha of the National Autonomous University of Mexico, have an advantage: They can place the detector right inside an underground tunnel that is thought to predate the pyramid itself.
In a paper submitted last month for online review, Menchaca-Rocha and his colleagues discuss simulations of data from the Pyramid of the Sun and mention the "poor quality of the experimental data at large angles." The references and the accompanying graphs imply that the team has started analyzing muon data but is not ready to draw any conclusions.
Muon detectors can be used to scope out nuclear waste sites ... check for smuggled nuclear materials ... or even look for the underground warning signs of a volcanic eruption. But Menchaca-Rocha's paper - as well as Schwitters' talk - make clear that hunting for ancient hidden chambers will require plenty of patience as well as careful calibration. Schwitters said it could be a few years before he had definitive findings from Belize.
The science is challenging, to be sure, but there's yet another reason why patience is required: The funding available for this kind of work just doesn't compare with the tens or hundreds of millions of dollars set aside for more traditional particle detectors such as the Compact Muon Solenoid. And that means the research is proceeding on a pay-as-you-go basis.
"The budget for this project is closer to archaeology than it is to high-energy physics," Schwitters said..