What is the heliopause?
≈ 120 AUfrom the Sun — about 18 billion km
The heliopause is the boundary where the solar wind — the Sun’s constant outflow of charged particles — is finally halted by the thin gas of interstellar space. It lies about 120 AU from the Sun (roughly 18 billion km), and only two spacecraft, Voyager 1 and Voyager 2, have ever crossed it.
▶ Follow Voyager past the heliopause
The edge of the Sun’s bubble — but not of the solar system
The Sun blows a vast bubble of charged particles and magnetic field called the heliosphere. The heliopause is that bubble’s outer skin: the place where the solar wind’s outward pressure finally balances the pressure of the interstellar medium, and the Sun’s wind gives way to the gas between the stars. Voyager 1 crossed it in August 2012 at about 121 AU; Voyager 2 followed in November 2018 at about 119 AU — our only two direct measurements ever.
Crossing the heliopause is not leaving the solar system. The Sun’s gravity holds comets in the Oort Cloud out to roughly 100,000 AU — nearly a thousand times farther. Voyager 1 will not reach that true gravitational edge for around 300 centuries.
By the numbers
Distance from the Sun
≈ 120 AU (18 billion km)
Voyager 1 crossing
August 2012, ~121 AU
Voyager 2 crossing
November 2018, ~119 AU
What stops there
the solar wind
What lies far beyond
the Oort Cloud, ~100,000 AU
Spacecraft to cross it
just two, ever
In the interactive view, Voyager 1 sits far beyond the planets — a labelled spark at its real, live-updating distance, still transmitting from the far side of the heliopause.
Keep going
✓ Facts verified July 2026
Every figure on this page is a real, rounded value checked against primary sources. Found something out of date? See how we keep it accurate.