(June 16, 2024)

But only two human-made objects have crossed the boundary of the solar system and entered interstellar space.

In 1977, NASA launched Voyager 1 and Voyager 2, equipped with tools to measure the magnetic fields and the particles it is directly passing through. After traveling for over three decades in space, they finally exited the outer layer of the heliosphere—heliopause in 2012 and 2018 respectively. They discovered that cosmic rays are about three times more intense outside the heliopause than deep inside the heliosphere.