Its deep vision has also enabled scientists to trace the story of how galaxies have changed through cosmic time.

BBC: Herschel space telescope to go blind

But Crawford and his colleagues believe the answer is to search for clues in relatively recent lava flows, because once cooled and covered over, they could preserve the mark of cosmic rays from the time they were exposed.

FORBES: Ancient Supernova Explosions Left Their Scars on Earth

Naturally occurring neutrinos from cosmic rays, supernovae and the sun stream through the detector at the same time.

ENGADGET: NOvA neutrino detector captures cosmic rays in 3D, aims to unlock the mysteries of the universe

It has been detecting a rise in the number of high-energy particles, or cosmic rays, coming towards it from interstellar space, while at the same time recording a decline in the intensity of energetic particles coming from behind, from our Sun.

BBC: Voyager Solar System 'exit' debated

They've dubbed it a cosmic ghost, and hope to get a better look at it next year when they can get some telescope time on the Hubble Space Telescope.

NPR: What Makes Our Solar System Special?