WASHINGTON — Patience and meticulous science were cause for celebration when an international team of scientists announced new results pointing to the possible detection of dark matter by a $2 billion cosmic ray observatory mounted on the exterior of the international space station.

Known as the Alpha Magnetic Spectrometer (AMS), the bus-size particle physics experiment has observed a striking pattern of antimatter particles called positrons that may turn out to be a product of collisions between dark matter particles.

“I think it is fair to say that this is the most important physics result thus far to come from the International Space Station,” theoretical physicist Robert Garisto, who was not involved in the AMS project but published the April 3 results, said via Twitter.

Although the James E. Webb Auditorium at NASA headquarters here was nearly empty during an April 3 press conference to announce the science results from the first 18 months of AMS operations, it did not stop space agency officials and scientists from enthusiastically unveiling the findings.

“There have been little glitches, but the end product is here for all of us to see and it’s a happy day,” Michael Salamon, AMS program manager at the U.S. Department of Energy’s Office of Science, said during the briefing.

By sifting through a year-and-a-half of data, scientists have found about 400,000 positrons — the antimatter partner particles of electrons — that are at the right energy to suggest they were created when particles of dark matter collided and annihilated each other.

“Some days, my job is really great, and this is one of those days where my job is really great,” William Gerstenmaier, NASA associate administrator for human exploration and operations, said.

Although the results might be exciting, the $2 billion detector that collected them almost never made it to space.

NASA canceled the AMS program due to concerns for astronaut safety in 2005, two years after the Space Shuttle Columbia accident.

The cancellation caused a backlash in the scientific community, leading Congress to approve funding for an extra shuttle mission to bring the instrument to the orbiting outpost.

“I guess it teaches us that patience is an important quality to have,” Gerstenmaier said. “There were times where we were uncertain about exactly what the future was going to be, we knew the quality of science was pretty strong and was pretty important and the team hung in there … and eventually things worked out.”

The AMS was launched to the international space station aboard Space Shuttle Endeavour in May 2011, and has been sending back data since its installation.

The particle physics experiment is led by Nobel laureate Samuel Ting, a physics professor at the Massachusetts Institute of Technology, with 200 scientists from 56 different institutions in 16 countries participating on the science team.

The results announced April 3 represent the first chunk of data published by the AMS science team.

“I think it’s just kind of the beginning of other great things that will come from this instrument on board space station,” Gerstenmaier said.

Dark matter is an invisible substance thought to make up more than 80 percent of the matter in the universe. Dark matter is difficult to detect because it rarely interacts with normal matter, except through its gravitational pull.

One of the leading explanations for dark matter is that it is made up of weakly interacting massive particles, or WIMPS, which may produce a detectable signature when they collide and annihilate each other.

Searching for this signature was one of the main motivations for building the Alpha Magnetic Spectrometer. Whether or not the instrument succeeds in detecting dark matter, scientists say they are happy with the early results from AMS so far.

“It’s a very major step forward by at least an order of magnitude in sensitivity,” said Brown University physicist Richard Gaitskell, a founding investigator on the Large Underground Xenon experiment, which aims to make a direct detection of dark matter particles.


Clara Moskowitz contributed from New York.