Voyager 1 is about to cross over into interstellar space having travelled almost 18 billion km since its launch from Earth in 1977.
The spacecraft has encountered a region of space where the intensity of high-energy particles hitting it from distant exploding stars has markedly increased. NASA scientists conclude that Voyager will soon reach its historic goal – crossing into interstellar space.
“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be,” said Ed Stone, Voyager project scientist at the California Institute of Technology.
“The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the solar system’s frontier.”
Between January 2009 and January 2012, there had been a gradual increase of about 25% in the amount of cosmic rays Voyager was encountering, said Stone. Since 7th May, cosmic ray hits have increased 5% in a week, and 9% in a month.
This increase is one of a three data sets which need to change significantly to indicate that Voyager is entering new territory. The second is a change in the intensity of energetic particles generated inside the heliosphere – the bubble of charged particles around the Sun. When Voyager breaks through the solar boundary, scientists expect this to decline precipitously.
The final clue will reveal a major change in the direction of magnetic lines surrounding the spacecraft. When in the heliosphere, these field lines run east-west, but when Voyager breaks into interstellar space, they are expected to run north-south.
“When the Voyagers launched in 1977, the space age was all of 20 years old,” said Stone. Many of us on the team dreamed of reaching interstellar space but we really had no way of knowing how long a journey would be – or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”
Voyager 1 and its sister spacecraft, Voyager 2, were launched to explore the outer planets – a task completed in 1989. Voyager 1 is on course to approach a star called AC +793888, aiming to come within two light-years of it while Voyager 2 is heading to a star named Ross 248.