Ancient secrets: scientist use high-tech methods to search for ancient treasures.

A giant pyramid looms above the ruins of an ancient city in central Mexico. The monument--called the amid of the Sun--was once the center of a bustling metropolis. But 1,500 years ago, the residents of Teotihuacan (TAY-oh-tee-hwa-KAHN) suddenly and mysteriously abandoned the city.

For hundreds of years, archaeologists have been studying the city's ruins, searching for clues about the people who lived there. Many scientists believe that the Pyramid of the Sun may house important relics. But they have failed to uncover its secrets.

Now, an unusual experiment could locate tombs or treasure-filled chambers that may be hidden inside the pyramid. Physicists have set up a lab beneath the ancient pyramid. There, they will use high-energy particles to "see" inside the solid monument.

RISE AND FALL

Nearly 2,000 years ago, large groups of people began settling in the city of Teotihuacan--northeast of present-day Mexico City. More than 125,000 people once lived in the city. But around 550-600 A.D., residents began abandoning it--burning many of its main buildings as they left.

Why did the city fall to ruin? "It looks like [there was] an internal revolt toward the people that were ruling," says Linda Manzanilla (mahn-za-NEE-ya), an archaeologist at the National Autonomous University in Mexico City, Mexico. But scientists still know little about these rulers. "We have found burial [sites], but no Teotihuacan ruler has ever been found," says Manzanilla. "I believe that the [remains of the] first rulers may be housed inside the Pyramid of the Sun."

LOST LEADERS

At 63 meters (207 feet) tall, the pyramid was the city's largest--and earliest--construction. Did the Teotihuacans bury the bodies of their earliest leaders inside? Uncovering evidence has proved difficult.

In the last 100 years, archaeologists have dug two tunnels into the piled soil and stone of the pyramid. But they have failed to find a buried tomb. "Then the digging in the pyramid stopped because there was no hint as to where to dig next," says Arturo Manchaca-Rocha (mahn-CHA-ka ROW-cha), a nuclear physicist at National Autonomous University.

TREASURE MAP 

Now, Manchaca-Rocha hopes that high-energy particles called muons (MEW-ons) will help pinpoint concealed chambers. These particles continually pummel Earth, harmlessly passing through anything in their path (see diagram, right). The particles travel most easily through objects or spaces with low densities--such as an empty or partially filled cavity. So if the pyramid holds a hollow tomb, more muons will zoom through that open area than through the solid soil surrounding it.

A detector, placed in a cave beneath the pyramid, will record the number of muons that pass through the pyramid. Just as X-ray images of your teeth reveal cavities, the detector's record of muon levels will help Manchaca-Rocha pinpoint chambers. "Then, we can tell the archaeologists where to dig," he says.

Manzanilla is anxiously awaiting the experiment's results--due in late 2006. "Teotihuacan was [Mexico's] first huge capital," she says. "It's important to find out how the people lived, how they were ruled, and why [their city] collapsed."

1. SPACE SHOWER

Cosmic rays from outer space constantly bombard Earth. These streams of high-energy particles collide with atoms (smallest unit of an element) in Earth's atmosphere. Result: Each atom's center, or nucleus, splits and releases smaller, subatomic particles. Among the particles formed from the collision are high-energy muons.

2. PARTICLE TRAIL

Whizzing toward Earth at almost the speed of light--roughly 300,000 kilometers (186,000 miles) per second--muons penetrate the pyramid. When passing through the solid rock, the particles lose energy and some get trapped. Muons passing through empty cavities travel to a detector located beneath the monument.

3. MAP MAKER

When a muon hits the detector, the particle produces a tiny electric charge. From this, the machine can determine the direction from which the muon traveled. If a cavity exists in the pyramid, the detector will record more muons passing through that area. By mapping the paths of the muons, the machine should be able to pinpoint a chamber.

DID YOU KNOW?

* In 1400 A.D., the Aztec discovered Teotihuacan. They gave the site and its monuments--including the Pyramid of the Sun-the names by which they are now known. Teotihuacan means "place of the gods."

* In the 1960s, a muon detector was used to examine the Chephren Pyramid near Cairo, Egypt. It was the first and only other experiment of this kind. Unfortunately, scientists did not find any chambers in the Chephren Pyramid that hadn't already been discovered.

CRITICAL THINKING:

* A muon detector will detect a chamber in the Pyramid of the Sun if the chamber is less dense than its surrounding material. Is it possible that the muon detector could miss important archaeological finds in the pyramid? How?

CROSS-CURRICULAR CONNECTIONS:

LANGUAGE ARTS: Research what archaeologists now know about the city of Teotihuacan, its buildings, and its residents. Then, write a story about a day in the life of a Teotihuacan resident. Be sure to describe his or her visit to the monuments of the city, including the Pyramid of the Sun.

RESOURCES

* Learn about other exciting archaeological finds in Teotihuacan at: www.archaeology.org/online/features/mexico/

* "The World's Oldest Physics Lab," by Sally Palmer, BBC Focus, August 2005.

(PAGE 18) ANCIENT SECRETS

DIRECTIONS: On a separate sheet of paper, use details from the article to help you write the following:

1. You are giving a school report on subatomic particles, and your classmates have never heard of muons. Explain to them what muons are.

2. You're an archaeologist studying Teotihuacan's ruins, and you're being filmed for a television show. Explain to the camera how you plan to use muons to uncover the secrets of the Pyramid of the Sun.

ANSWERS

Answers will vary but should include the following points:

1. Cosmic rays from outer space constantly bombard Earth. These streams of high-energy particles collide with atoms in Earth's atmosphere Result: Each atom's center, or nucleus, splits and releases smaller, subatomic particles. Among the particles formed are high-energy muons. These particles speed toward Earth at almost the speed of light--roughly 300,000 kilometers (186,000 miles) per hour.

2. Muons continually pummel Earth, harmlessly passing through anything in their path. When the muons penetrate solid rock, such as the pyramid's structure, the particles lose energy and some get trapped. Muons passing through empty cavities travel through the pyramid to a detector located beneath the monument. When a muon hits the detector, the particle produces a tiny electric charge. From this, the machine can determine the direction from which the much traveled. If a cavity exists in the pyramid, the detector will record more muons passing through that area. By mapping the paths of the muons, the machine should be able to pinpoint a chamber in the pyramid.