NASA's Voyager 1, launched in 1977, was propelled into deep space with the help of Jupiter's and Saturn's gravity. Now it is about to leave the solar system. But exactly when is unclear.

Voyager 1 is traveling at a speed of about 3.6 Astronomical Units (AU) per year - one 'AU' equals the distance between the Sun and the Earth, or 93 million miles.

The data making the 16-hour-38 minute, 11.1-billion-mile journey from Voyager 1 to antennas of NASA's Deep Space Network on Earth detail the number of charged particles measured by the two High Energy telescopes aboard the spacecraft. These energetic particles were generated when stars in our cosmic neighborhood went supernova and they indicate that it has encountered a region in space where the intensity of charged particles from beyond our solar system has markedly increased. Voyager scientists looking at this rapid rise draw a historic conclusion – that humanity's first emissary to interstellar space is on the edge of our solar system will soon enter a fluid region of space known as the heliosheath, which is past the boundaries of the termination shock. This is a violent zone where interstellar gas and solar wind start to mix. It is possible that before its electrical power is exhausted, Voyager 1 will pass through the heliopause region and into interstellar space.

Where is Voyager 1?
Where is Voyager 1?  Credit: NASA

There's a debate going on between scientists, depending on how they've analyzed Voyager's data, about whether it has passed beyond the termination shock or not. According to Dr. Stamatios Krimigis, Voyager 1 has crossed the termination shock,  while Dr. Frank McDonald of the University of Maryland says that the Voyagers are on the threshold of the termination shock, but have not left the solar wind.

During the next 20 years, as Voyager continues on its travels in the Milky Way, new discoveries will be be made - even if we don't know about them. If alien life forms are out there, Voyager has a 12-inch gold-plated copper disc with recorded sounds and images of Earth, chosen by a committee chaired by Carl Sagan, designed to portray the diversity of life and culture on the planet. Instructions explaining where the spacecraft originated and how to play the disc are engraved onto an accompanying cover. They even included a cartridge and a needle, if you are old enough to remember how phonographs work.


Where Voyager has been so far.  Credit: NASA

The final data set that Voyager scientists believe will reveal a major change is the measurement in the direction of the magnetic field lines surrounding the spacecraft. While Voyager is still within the heliosphere, these field lines run east-west. When it passes into interstellar space, the team expects Voyager will find that the magnetic field lines orient in a more north-south direction. Such analysis will take weeks, and the Voyager team is currently crunching the numbers of its latest data set.

 "When the Voyagers launched in 1977, the space age was all of 20 years old," said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. "Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be -- or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”