The nano-missiles, no bigger than a blood cell, yet weighing more than a ton, are so rare the chance of their hitting anybody is infinitesimal, and are so tiny "they wouldn't make holes big enough to bleed," researcher Eugene Herrin, a seismologist at Southern Methodist University, told United Press International.
"I don't think you'd want to be hit in the head with one, though ... It might really ring your bell," Herrin said.
Strange matter draws its name from its heavy constituents, so-called strange quarks. Quarks are the building blocks of atomic nuclei, and when comprising ordinary matter, quarks come only in two "flavors," as scientists call their characteristics, "up" or "down." For more than a decade, however, theorists have suggested some matter might contain quarks of a third flavor -- "strange" -- which could have emerged from the cosmic fireball of the Big Bang and survived as tiny but massive and as-yet-undetected nuggets up to the present day.
The Big-Bang theory suggests the universe began with the explosion of a superdense primeval fireball and has been expanding ever since.
If the nuggets are indeed made up of strange quarks, they would have to be extremely heavy. Strange quarks are roughly 20 to 40 times more massive than their up and down brethren and can cluster together more densely -- only a cubic centimeter of strange matter would weigh about 110 million tons.
The research team reasoned if a population of strange nuggets exists in outer space, mathematical estimates suggest the one-ton nuggets should punch through Earth approximately once a year. As they punch through the planet, they might leave a sound wave signature earthquake detectors could pick up.
"You could use the Earth as a detector," Herrin told UPI.
The scientists combed through more than 1 million U.S. Geological Survey reports from 8,000 seismic stations around the world taken from 1990 to 1993. In all that information, the scientists found two clusters of instances they think provide strong evidence for strange nuggets streaking through rock at hypersonic speeds.
The reports contained detected seismic waves about equal in strength to those of underground explosions of about 1,000 tons of TNT, set off at depths of 3,100 miles. Each set of reports consisted of sound wave signals collected at seven to nine seismic stations.
When the seismic wave sources were compared, the researchers said, the data formed a line, as if an object causing the waves was traveling through the Earth. One apparently entered Antarctica and exited south of India in a span of 27 seconds, while a second tunneled in somewhere in the South Pacific and exited from Antarctica in 19 seconds.
"We are aware of only one model that predicts seismic line events with a frequency of one or two a year ... the passage of nuggets of strange quark matter through the Earth."
The scientists have submitted their research to the Seismological Society of America.
Herrin said his team is now working on how strongly strange nuggets would interact with normal matter.
"It's certainly an exciting idea, but we need to check it out very carefully," said seismologist Paul Richards of Columbia University's Lamont Doherty Earth Observatory in the Palisades, N.Y.
"One phrase I heard was 'Extraordinary results require extraordinary proof'," Richards said.
(Reported by Charles Choi in New York.)