There is no clear definition for the edge of the solar system[1]. The Voyager spacecraft are helping to define it. The heliopause is a pretty reasonable way to

There is no clear definition for the edge of the solar system[1]. The Voyager spacecraft are helping to define it. The heliopause is a pretty reasonable way to define the edge of the solar system. A stated goal of the Voyager mission is to search for the heliopause boundary[2]: Both Voyagers are headed towards the outer boundary of the solar system in search of the heliopause, the region where the Sun's influence wanes and the beginning of interstellar space can be sensed. The heliopause has never been reached by any spacecraft; the Voyagers may be the first to pass through this region, which is thought to exist somewhere from 8 to 14 billion miles from the Sun. This is where the million-mile-per-hour solar winds slows to about 250,000 miles per hour—the first indication that the wind is nearing the heliopause. The Voyagers should cross the heliopause 10 to 20 years after reaching the termination shock. That having been said, this is a poor title. The news is not that the spacecraft has simply crossed a boundary. The news is that the boundary, until now unknown, was discovered (potentially). The difference is "Ship successfully crosses Atlantic Ocean" vs "Columbus discovers New World". Perhaps a better title would be "More evidence that Voyager 1 has found the heliopause, considered to be the edge of the solar system". ---- [1] http://en.wikipedia.org/wiki/Solar_System#Farthest_regions http://en.wikipedia.org/wiki/Solar_System#Farthest_regions [2] http://voyager.jpl.nasa.gov/mission/interstellar.html http://voyager.jpl.nasa.gov/mission/interstellar.html