Sen— Voyager 1 is within sight of the ocean of interstellar space, according to NASA.
After 35 years cruising through our solar system, the probe discovered a new phenemonon: a "magnetic highway". It's thought to be at the extreme edge of the heliosphere, or the magnetic region of space dominated by the Sun.
The size of the highway, and the time it will take to cross it, are both unknowns. It could be months or years, NASA officials said in a televised press briefing Monday.
"This is another exciting step in the Voyager journey of exploration," said Edward Stone, a Voyager project scientist who works at the California Institute of Technology. "This is a new region of the heliosphere that we did not realize was there."
The Voyager spacecraft are in the heliosheath, which is the outer edge in the "bubble" of charged particles surrounding Earth's sun. Credit: NASA/JPL-Caltech
NASA launched twin Voyager spacecraft in 1977 to take advantage of a rare planetary alignment. A spacecraft, properly pointed, could slingshot from one planet to the next using gravity.
The spacecraft sped past the outer planets in the solar system, taking close-up views of Jupiter, Saturn, Neptune, Uranus and their moons. Among other discoveries, the Voyagers found volcanos on the Jupiter moon Io, and discovered that the moon Titan (orbiting Saturn) has a thick, orange atmosphere.
Voyager 1 is now about 18 billion miles from the Earth, the equivalent of 123 Earth-sun distances away. Its twin, Voyager 2, is 15 billion miles from the planet.
The "magnetic highway" Voyager 1 found is a region where charged particles flowing along the Sun's magnetic lines meet magnetic lines that come from interstellar space, outside of the heliosphere.
According to scientists, the connection between these magnetic fields allows particles to flow in and out of the heliosphere.
This region was not anticipated by scientists and came as a surprise to the Voyager team.
"As this discovery demonstrates, there are things that aren’t in our thinking," Stone said.
While Voyager 1 breaches the interstellar barrier, NASA is using other spacecraft - located much closer to Earth - to map better the boundary.
The Interstellar Boundary Explorer (IBEX), launched in 2008, detects neutral atoms coming from this area. It looks over the entire sky from its perch in Earth orbit.
"The one downside with IBEX is it's inexpensive, and not in ideal orbit for making observations," Stone pointed out, but added that further measurements are possible with the Cassini spacecraft currently orbiting Saturn and its moons.
As for Voyager itself, the spacecraft's instruments are still in good health. The hardy spaceship's biggest threat is the decaying power available from its radioactive source.
Power will dwindle through the coming years, at a rate of four watts annually, NASA said. By 2020, certain instruments will need to be turned off. The spacecraft will fall silent around 2025.
It will take another 40,000 years for Voyager 1 to reach another star. Even then, it will pass by a distant 1.6 light years away as it continues wandering the cosmos.