A massive science instrument that is spinning the globe aboard the International Space Station has provided its first glimpse of what may be mysterious dark matter in the universe, experts said Wednesday.

The first results from the Alpha Magnetic Spectrometer, the most sensitive particle physics spectrometer ever sent to space, seem to indicate "evidence of a new physics phenomena," said a press statement from the international research team.

Just what it is will require more research, and is not yet a definitive finding but is the first of many reports expected to come from the AMS, built by an international team from 16 countries.

The data published in the journal Physical Review Letters comes from 25 billion cosmic ray events compiled since the AMS arrived at the orbiting outpost aboard the space shuttle Endeavour's final flight in 2011.

NASA was to hold a press conference later Wednesday to discuss the findings.

The AMS studies cosmic rays -- which are charged high-energy particles that permeate space -- before they interact with Earth's atmosphere.

The first hints of excess antimatter in the cosmic ray influx were observed about two decades ago, but its origin remains a mystery.

Dark matter -- which makes up about a quarter of the universe -- has never been directly detected before, but has been observed indirectly through its interaction with visible matter.

Of the 25 billion cosmic ray events the AMS has studied, "an unprecedented number, 6.8 million, were unambiguously identified as electrons and their antimatter counterpart, positrons," said a press release from CERN, the European Organization for Nuclear Research.

"Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin," AMS spokesman Samuel Ting said in a statement.