The heliopause is the boundary where the Sun’s influence ends and interstellar space begins. It’s the outer edge of the heliosphere, which is the vast bubble created by the solar wind—a stream of charged particles emitted by the Sun.
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Where exactly is the heliopause?
The location isn’t fixed, but on average, it lies at about:
- 121 astronomical units (AU) from the Sun for Voyager 1, which crossed it in August 2012.
- 119 AU for Voyager 2, which crossed it in November 2018.
(1 AU = the distance from the Earth to the Sun, about 150 million km or 93 million miles.)
However, the distance varies:
- It can shrink or expand depending on solar activity (solar wind pressure).
- It’s closer to the Sun in the direction facing the interstellar wind and further on the opposite side—like a comet-shaped bubble.
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What lies beyond?
Beyond the heliopause is interstellar space—the space between stars in our galaxy. This region contains:
- The interstellar medium (a thin soup of gas, dust, and cosmic rays),
- Magnetic fields from the Milky Way,
- And perhaps evidence of how other stellar winds interact with the Sun’s.
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Voyagers and the Heliosphere
- Voyager 1, now ~163 AU away, is the first human-made object in interstellar space.
- Voyager 2, now ~145 AU, provides complementary data from a different trajectory.
- They both still send back signals, traveling at the speed of light—though it takes over 20 hours for one message to reach Earth.
Would you like a visual sketch or conceptual diagram of the heliosphere and heliopause?
