MCQ Detailed View

The heliopause is the boundary in our Solar System where the pressure of the solar wind becomes equal to the opposing pressure of the interstellar medium. The solar wind is a stream of charged particles constantly released by the Sun, forming a protective bubble around our Solar System called the heliosphere. This bubble shields planets from a large amount of cosmic radiation and high-energy particles coming from outside the Solar System.

As the solar wind travels away from the Sun, its pressure gradually decreases. At a very large distance—about 120 astronomical units (AU) from the Sun—the outward push of the solar wind becomes weak enough that it balances with the inward pressure of the thin gas and plasma found in interstellar space. This balance point is called the heliopause.

Beyond the heliopause lies interstellar space, where the Sun’s influence is no longer dominant. This region marks the outermost boundary of the heliosphere and is considered the edge of the Solar System’s influence, though gravitationally the Sun's reach extends farther.

The heliopause is not a fixed barrier; its location can change depending on solar activity. When the Sun emits stronger solar winds, the boundary can expand, and when the solar wind weakens, it can contract slightly.

The Voyager 1 spacecraft crossed the heliopause in 2012, followed by Voyager 2 in 2018. These were the first human-made objects to enter interstellar space, providing direct measurements of this boundary.

Key facts:

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  Heliopause: Outer edge of the heliosphere.

  
  


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  Distance: Around 120 AU from the Sun.

  
  


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  Significance: Marks where solar wind pressure equals interstellar medium pressure.

  
  

Thus, the correct answer is C. Heliopause.