Assertion: cosmic ray's source | /r/HasProperty | mystery
Facets:
value: currently
type: TEMPORAL
value: for many years
type: TEMPORAL
Source sentences:
text: The source of such high energy particles has been a mystery for many years.
text: I know that the source of UHECR's above the ankle is currently a mystery.
text: But the source of ultrahigh-energy cosmic rays – which are mostly bare protons – is a mystery.
text: The sources of these cosmic rays are a mystery.