NASA scientists and the space-loving public are eagerly awaiting the moment when the unmanned Voyager 1 spacecraft becomes the first vessel in human history to exit the solar system, which is expected some time in the next few years at the latest. But with a number of false positives of that milestone in recent months, NASA is taking a step to make sure when the Voyager clears the boundary of the solar system, people will know for sure.

The agency has added a new tracker gauge to its Voyager home page, showing the levels of cosmic rays Voyager 1 -- and the twin spacecraft following behind it, Voyager 2 -- are detecting from inside and outside the heliosphere, the bubble of Sun-charged particles that encases our solar system. When the cosmic rays from outside spike, and the ones from inside fall and stay that way, that means Voyager 1 is reaching the beginning of interstellar space.

So far, the gauge for Voyager 1 shows that cosmic rays from outside have exceeded those from inside, but not completely tipped in the balance of the outside cosmic rays. Even in that case, scientists still need another indicator — a definitive change in the magnetic field of the local region of space — to call Voyager's departure for certain. Still, the tracker should help people keep a closer watch on Voyager's journey into the unknown.