Voyager 2 joins its twin in interstellar space

Voyager 2, the multi-planetary exploratory probe launched in 1977, has finally entered interstellar space, some six years after its twin, Voyager 1, did the same. It’s now about 11 billion miles from Earth, the second-farthest-out human-made object in space.
Interstellar space starts where the sun’s “heliosphere” ends — the big ball of radiation and plasma in which the planets bathe and by which they are protected. Both Voyagers have instruments on board that monito