Voyager 1 Crossed Heliopause at 122 AU, Reaching Interstellar Space in 2012

3 articles · Updated · spacedaily.com · Jul 15

25 August 2012 marked Voyager 1’s entry into interstellar space at about 122 astronomical units, roughly 18 billion km from the Sun; NASA confirmed the crossing on 12 September 2013.
Science papers tied the crossing to a near-vanishing of low-energy solar particles and a sharp rise in galactic cosmic rays, even as the boundary appeared to flex past the spacecraft for about 30 days.
A key expected signal failed: the magnetic field strengthened but shifted by no more than 2 degrees, undermining the textbook idea that the heliopause would show a clean directional rotation.
A March 2012 coronal mass ejection provided the clincher when its shock reached Voyager 1 in April 2013, letting scientists infer plasma density more than 40 times higher than inside the heliosphere.
Voyager 2’s 2018 crossing at about 119 AU backed the picture of a sharp yet porous boundary and a thinner-than-expected outer layer, while the missing magnetic-field rotation remains unexplained.