Hi,

Although a lot of people tend to think of the Sun's energy as the light it puts out (e.g., how we use it for solar power), but a lot of the Sun's energy is actually in its magnetic fields. While sunlight is very weak at the outer planets (making it very difficult to use solar panels for spacecraft power if the mission is going to Jupiter and beyond), the Sun's magnetic fields and solar wind (charged particles that flow away from the Sun at about 1 million mph) exert their influence way past all our planets and past Pluto. This region is called the heliosphere.

The point at which the pressure from the Sun's magnetic fields and solar wind finally weakens enough to be equal to the pressure from interstellar space is called the heliopause. The spacecraft Voyager 1 actually flew beyond this point in 2012. At that time it was 11 billion miles from Earth.

-Christina

Hello! My co-workers at the University of Iowa built the Voyager Plasma Wave Science instrument that made the observations showing that Voyager had reached the heliopause. You can listen to space sounds from Voyager crossing the heliopause here: http://www-pw.physics.uio...nterstellar_epo.html