This undated file image provided by the European Space Agency ESA on Wednesday April 3, 2013 shows the International Space Station in the sunlight. A $2 billion cosmic ray detector on the International Space Station has found the footprint of something that could be dark matter, the mysterious substance that is believed to hold the cosmos together but has never been directly observed, scientists say. But the first results from the Alpha Magnetic Spectrometer, known by its acronym AMS, are almost as enigmatic as dark matter itself. They show evidence of new physics phenomena that could be the strange and unknown dark matter or could be energy that originates from pulsars, scientists at the European particle physics laboratory near Geneva announced Wednesday April 3, 2013. (AP Photo/NASA/European Space Agency ESA. Keystone)
This undated file image provided by the European Space Agency ESA on Wednesday April 3, 2013 shows the International Space Station in the sunlight. A $2 billion cosmic ray detector on the International Space Station has found the footprint of something that could be dark matter, the mysterious substance that is believed to hold the cosmos together but has never been directly observed, scientists say. But the first results from the Alpha Magnetic Spectrometer, known by its acronym AMS, are almost as enigmatic as dark matter itself. They show evidence of new physics phenomena that could be the strange and unknown dark matter or could be energy that originates from pulsars, scientists at the European particle physics laboratory near Geneva announced Wednesday April 3, 2013. (AP Photo/NASA/European Space Agency ESA. Keystone)
FILE - In this July 25, 2012 file picture Director general of CERN Rolf-Dieter Heuer, left, Nobel laureate and AMS spokesperson Samuel C.C. Ting, right, and Mark Kelly, NASA astronaut and commander of mission STS-134, center, brief the media at the Alpha Magnetic Spectrometer (AMS) Payload Operations and Command Center (POCC) at the European Organization for Nuclear Research (CERN) in Meyrin near Geneva, Switzerland. A US $2 billion experiment on the International Space Station is on the verge of explaining one of the more mysterious building blocks of the universe: The dark matter that helps hold the cosmos together. An international team of scientists says the cosmic ray detector has found the first hint of dark matter, which has never yet been directly observed. The team said Wednesday its first results from the Alpha Magnetic Spectrometer, flown into space two years ago, show evidence of a new physics phenomena that could be the strange and unknown matter. Nobel-winning physicist Samuel Ting, who leads the team at the European particle physics laboratory near Geneva, says he expects a more conclusive answer within months. The findings are based on an excess of positrons positively charged subatomic particles. (AP Photo/Keystone/Martial Trezzini,File)
FILE -In this undated picture made available by NASA, a technician examines the Alpha Magnetic Spectrometer at Kennedy Space Center in Cape Canaveral, Fla.. The cosmic ray detector was mounted on the International Space Station, searched the universe and shall help to explain how everything came to be. CERN , the European Organization for Nuclear Research, released first results of the experiment Wednesday April 3, 2013. (AP Photo/NASA, Glenn Benson)
FILE - This undated image shows an artist's concept of the Alpha Magnetic Spectrometer, rounded module at left, installed on the International Space Station provided by NASA. The cosmic ray detector searched the universe and shall help to explain how everything came to be. CERN , the European Organization for Nuclear Research, released first results of the experiment Wednesday April 3, 2013. (AP Photo/NASA)
GENEVA (AP) ? It is one of the cosmos' most mysterious unsolved cases: dark matter. It is supposedly what holds the universe together. We can't see it, but scientists are pretty sure it's out there.
Led by a dogged, Nobel Prize-winning gumshoe who has spent 18 years on the case, scientists put a $2 billion detector aboard the International Space Station to try to track down the stuff. And after two years, the first evidence came in Wednesday: tantalizing cosmic footprints that seem to have been left by dark matter.
But the evidence isn't enough to declare the case closed. The footprints could have come from another, more conventional suspect: a pulsar, or a rotating, radiation-emitting star.
The Sam Spade in the investigation, physicist and Nobel laureate Sam Ting of the Massachusetts Institute of Technology, said he expects a more definitive answer in a matter of months. He confidently promised: "There is no question we're going to solve this problem."
"It's a tantalizing hint," said California Institute of Technology physicist Sean Carroll, who was not part of the team. "It's a sign of something." But he can't quite say what that something is. It doesn't eliminate the other suspect, pulsars, he added.
The results from the Alpha Magnetic Spectrometer, or AMS, are significant because dark matter is thought to make up about a quarter of all the matter in the universe.
"We live in a sea of dark matter," said Michael Salamon, who runs the AMS program for the U.S. Energy Department. Unraveling the mystery of dark matter could help scientists better understand the composition of our universe and, more particularly, what holds galaxies together.
Ting announced the findings in Geneva at the European Organization for Nuclear Research, the particle physics laboratory known as CERN.
The 7-ton detector with a 3-foot magnet ring at its core was sent into space in 2011 in a shuttle mission commanded by astronaut Mark Kelly while his wife, then-Rep. Gabrielle Giffords, was recovering from a gunshot wound to the head. The device is transmitting its data to CERN, where it is being analyzed.
For 80 years scientists have theorized the existence of dark matter but have never actually observed it directly. They have looked for it in accelerators that smash particles together at high speed. No luck. They've looked deep underground with special detectors. Again no luck.
Then there's a third way: looking in space for the results of rare dark matter collisions. If particles of dark matter crash and annihilate each other, they should leave a footprint of positrons ? the anti-matter version of electrons ? at high energy levels. That's what Ting and AMS are looking for.
They found some. But they could also be signs of pulsars, Ting and others concede. What's key is the curve of the plot of those positrons. If the curve is one shape, it points to dark matter. If it's another, it points to pulsars. Ting said they should know the curve ? and the suspect ? soon.
The instrument will be measuring cosmic rays, where the footprints are found, until 2020 or so.
Other scientists praised the results and looked forward to more.
"This is an 80-year-old detective story and we are getting close to the end," said University of Chicago physicist Michael Turner, one of the giants in the field of dark matter. "This is a tantalizing clue and further results from AMS could finish the story."
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Borenstein reported from Washington.
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Online:
NASA: http://www.nasa.gov/shuttle
Alpha Magnetic Spectrometer: http://www.ams02.org
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