noun. The outer boundary of the heliosphere.

noun. The boundary of heliosphere where the Sun's solar wind is stopped by the interstellar medium.

noun. the boundary marking the edge of the sun's influence; the boundary (roughly 100 AU from the sun) between the interplanetary medium and the interstellar medium; where the solar wind from the sun and the radiation from other stars meet

"This border, called the heliopause, is a bubble-shaped boundary surrounding our solar system where the solar wind’s strength is no longer great enough to push back the wind of other stars."

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