After decades and many false claims, NASA researchers are finally confident that the spacecraft, Voyager 1 has left the Solar System. Originally launched in 1977, the craft is now approximately 12 billion miles away, or 17 light hours. Its twin, Voyager 2 is only 9.5 billion miles away, but it may reach interstellar space soon.
For some time now, claims have been made that Voyager 1 had finally escaped the Solar System, but these were ultimately proven false. Part of the reason for this is that we do not really know the physics going on at the edge of the heliosphere, the outermost boundary of the Solar System. Within it, the effects of the Sun are greater than the effects of interstellar space, but distinguishing between them has been proving difficult. Not helping matters is that Voyager 1 does not have a working plasma sensor. Fortunately the Sun helped out by firing a coronal mass ejection in March 2012, and thirteen months later it reached Voyager 1. The magnetic fields of the ejection caused the plasma surrounding Voyager to vibrate in a way it can detect.
After pouring over the data, the researchers finally concluded that the density of the plasma means it has to have originated from interstellar space, and not the Solar System. Looking at past data with the new theory, the researchers have also determined that the spacecraft likely exited the Solar System just over a year ago, in August of 2012. Now the hope is that we will continue to receive signals from humanity's first interstellar spacecraft until 2020, or longer.