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It's a classic whodunit, with cosmic proportions.

Something - or someone - out there is hurling incredibly energetic particles around the universe. Scientists and engineers have gathered in Chicago this week to develop a plan to track these "ultra-high-energy cosmic rays" back to their source."This is totally inexplicable," said Nobel laureate James Cronin, a physicist from the University of Chicago. "We've learned so much about the sky and about the cosmos, but this is a puzzle. The scientist is always extremely interested in looking at things that are totally unexplainable."

Cosmic rays are nothing new. They are made up of protons - usually contained in the nuclei of atoms - that are shot out of supernovas from within the Milky Way galaxy. The particles bounce off magnetic clouds in space and gain energy as they go along. Many reach Earth, where they constantly bombard humans at nearly the speed of light.

The atmosphere filters some out, and earthbound creatures have developed a general tolerance to those that get through. Still, scientists believe the constant radioactive bombardment is partly responsible for the genetic mutations that occur in nature.

High- and ultra-high-energy cosmic rays, however, defy explanation. The particles striking Earth have 100 million times the energy produced by the world's most powerful particle accelerator, at Fermilab in the Chicago suburb of Batavia.

Scientists know of no source - not supernovae, not black holes - that can produce such energies. They believe they come from outside our galaxy.

Scientist Pierre Auger first speculated about the possibility of high-energy cosmic rays in 1938. It wasn't until 1991, however, in an experiment in Utah, that an ultra-high-energy cosmic ray was recorded - and it had six times more energy than was believed possible.

Since high-energy cosmic rays are rare - the particles strike any given square kilometer about once a century - harmful effects are probably nonexistent, Cronin said Tuesday.

Alan Watson, professor of physics at the University of Leeds in England, said the team of about 100 scientists, who include eight physicists from the University of Utah, hopes to design two devices to detect the rays and provide insight into where they come from.

One might be built in Utah, possibly at Dugway Proving Ground, the Utah scientists said.

"(Each) will cover an area of land about the size of the state of Delaware, one in the northern hemisphere and one in the southern hemisphere," Watson said.

Direct observation of cosmic rays is possible only above the Earth's atmosphere. Because the high-energy cosmic rays are so rare, a space-based detector has been ruled out.

The ground-based detectors, about 3,000 clustered together over 5,000 square miles, will be solar-powered and observe cosmic ray shower particles.

When particles hit the detectors, a computer will confirm whether they are part of a large shower, then transmit data about their direction and strength to a central computer. Scientists hope to measure about 50 events a year over 10 to 20 years.

The detectors also will record the faint light caused by the particles' collision with air molecules.

"With these methods, we will be able to make maps of the universe and figure out the particular directions" of the high-energy cosmic rays, Watson said.

Sites for the projects, which are expected to cost about $50 million, will be announced in early August, Cronin said. Possible locations include the southwest United States, Spain, Russia, Argentina and South Africa.

Paul Sommers of the University of Utah said Utah is the most likely southwest U.S. site. "Dugway is possible," he said.

Utah is a promising site because of the Fly's Eye cosmic-ray detector already in place at Dugway. Fly's Eye could be incorporated into the new detector at a 20 percent cost saving.

However, Dugway's mountains could intefere with line-of-sight cellular phone communications among the 3,000 particle counters, so if Utah is chosen, the project might be built elsewhere in the western desert, Sommers said.

It was Fly's Eye that detected the high-energy cosmic ray in 1991.