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What Marks the Outer Boundary of Our Solar System

Solar winds flow out from the sun in all directions creating the heliosphere, a bubble surrounding the solar system. This bubble, containing the solar system, moves through space as the universe expands. According to Southwest Research Institute's Dave McComas, the solar system has three boundaries on the edge of the heliosphere. They are the bow shock, termination shock and heliopause.

The Bow Shock
- The solar system moving through the interstellar medium creates wave or bow shock in space.
  
  The bow shock precedes the heliosphere as it moves through space and occurs at the juncture between the solar system and interstellar space. Like a ship's bow, the heliosphere creates a wave in space. This wave is the bow shock. Interstellar space is not empty. It contains the interstellar medium (ISM) consisting of dust, helium and hydrogen. It also contains energy particles known as cosmic rays. Interstellar space exists between solar systems within a galaxy. The sun's solar winds flow out past the planets. When the solar wind meets the ISM, it creates a bow shock or wave and marks the outer boundary of the solar system.
Termination Shock
- Solar winds from the sun flow past the Earth on their way to the solar system's boundary.
  
  The solar winds move between 700,000 and 1,500,000 miles per hour as they speed past the Earth on their way into interstellar space. As they reach the outer boundary of the solar system, the incoming interstellar winds act in opposition and cause them to slow down. Scientists call this area of slowing solar winds the termination shock.
Heliopause
- The heliopause occurs between the termination shock and the bow shock. At this point, the solar wind and the interstellar winds balance each other. Beyond the heliopause is interstellar space. Once an object passes through the heliopause, it is no longer in the solar system.
Voyager Spacecraft
- Both the Voyager spacecrafts went past Saturn on their way to the solar system's boundary.
  
  Voyager 1 and 2 spacecrafts were launched in 1977. They collected data from several planets on their way to the solar system's boundary. Voyager 1 flew by Saturn; Voyager 2 went by Jupiter, Saturn, Uranus and Neptune. Voyager 1 has gone the farthest of any spacecraft launched from Earth. Their batteries will last until 2020. At that time, NASA predicts Voyager 1 will be 13 billion miles from Earth and beyond the solar system's boundary.
Interstellar Boundary Explorer
- Interstellar energy particles could cause DNA to mutate.
  
  The Interstellar Boundary Explorer (IBEX) was launched in October 2008. Its mission is to map the solar system's boundaries. It is currently returning pictures of the heliosheath, the region between the termination shock and the heliopause. According to NASA,the heliosheath is located 10 billion miles from the Earth and blocks interstellar particles from hitting the Earth. These particles could be hazardous to life on Earth by causing DNA mutations.

Astronomy