Glossary / Space
Heliopause
The boundary where the flow of particles from the Sun (the solar wind) is stopped by the gas between the stars — one definition of the outer edge of the solar system.
The region reached by the solar wind — the heliosphere — wraps the solar system like a bubble, with interstellar space beyond. In August 2012, about 120 astronomical units from the Sun, the particles of solar origin measured by Voyager 1 dropped sharply while cosmic rays from the galaxy rose. Edward Stone and colleagues concluded that the spacecraft had left the heliosphere[1].
It was the first human-made object to leave the Sun's sphere of influence. Voyager 2 followed in 2018.
Related terms
- Gravity assistUsing a planet's gravity and orbital motion to change a spacecraft's speed or direction without fuel as it flies past.
- Van Allen beltDoughnut-shaped regions where high-energy protons and electrons are trapped by Earth's magnetic field. There is an inner and an outer belt.