The tireless Voyager 1 spacecraft, launched in the disco era and now about 19 billion km from Earth, has become the first man-made object to enter interstellar space, scientists said Thursday.
Interstellar space, scientists now know with certainty, is dense with particles, and the place is literally hissing — or maybe you could say it is whistling in the dark.
"It's almost a pure tone — like middle C, but slightly varying, like your piano is not quite tuned right," said Donald Gurnett, a University of Iowa physicist who has been working on the Voyager mission most of his adult life.