Since the Alpha Magnetic Spectrometer (AMS) was installed in May last year it has been gathering data from millions of light years beyond our galaxy, the Milky Way.
Until now, scientists have only been able to theorise the existence of dark matter, which makes up around 26% of the universe.
Its ghostly presence around galaxies exerts a gravitational effect that can be measured and observed as rings, but what it is made of remains to be proven.
The findings announced by Nasa reveal a positron spike "consistent" with the kind of interaction expected by one theory relating to dark matter.
But the scientists say the evidence is not yet "sufficiently conclusive" to rule out other explanations