(LONDON GUARDIAN) Twelve billion miles from Earth, there is an elusive boundary that marks the edge of the sun’s realm and the start of interstellar space. When Voyager 2, the longest-running space mission, crossed that frontier more than 40 years after its launch it sent a faint signal from the other side that scientists have now decoded.
The Nasa craft is the second ever to travel beyond the heliosphere, the bubble of supersonic charged particles streaming outwards from the sun. Despite setting off a month ahead of its twin, Voyager 1, it crossed the threshold into interstellar space more than six years behind, after taking the scenic route across the solar system and providing what remain the only close-up images of Uranus and Neptune.
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Now Voyager 2 has sent back the most detailed look yet at the edge of our solar system – despite Nasa scientists having no idea at the outset that it would survive to see this landmark.