the.com/heliosphere

means The vast bubble of charged particles and magnetic field blown outward by the sun, marking the boundary where solar wind gives way to interstellar space.

from Built from Greek 'helios' (sun) and 'sphere' (ball, globe) — the same pairing of classical roots astronomers use for magnetosphere and atmosphere. The term itself is modern, coined in the 20th century as space physicists began mapping solar wind and needed a word for the sun's zone of influence, finally confirmed by spacecraft like Voyager that crossed its outer edge, the heliopause.