In September 1977, Voyager 1 was launched to space on a journey to visit Jupiter and Saturn, before heading out to the stars. NASA’s robotic explorer reached the heliopause — leaving the solar system (by one major standard) — in 2012. Now, a new study focused on a hum heard by the intrepid space shows this overlooked signal could tell us a great deal about the distant void lying outside our solar system. Voyager 1 is now over 22.5 billion kilometers (14 billion miles) from Earth, soaring through a diffuse mixture of particles and gas called the interstellar medium. This hum,…

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