NASA officially announced that Voyager 1 had entered interstellar space — a moment decades in the making. The evidence came from plasma wave data collected in late 2012 / early 2013, showing a dramatic jump in plasma density consistent with leaving the heliosphere. For context, Voyager 1 was about 122 AU from the Sun (that’s ~11 billion miles).
The announcement wasn’t sudden. Back in 2012, scientists saw a “magnetic highway” of charged particles, but the official “we are out ” confirmation came in September 2013 after careful analysis. There was even healthy scientific debate: some argued Voyager hadn’t truly left until it measured a change in magnetic field direction (which didn’t happen as expected). But the plasma density data won the case — Voyager 1 was in a new, unexplored region.
In 2013, Voyager 2 was still inside the heliosphere (~100 AU), but closing in. It would eventually cross into interstellar space in 2018.
Revisiting Voyager 2013 – The Little Mission That Keeps on Giving
