NASA has confirmed that the Voyager 1 spacecraft has reached interstellar space. The discussion went on for almost a year because it’s uncharted territory which, as it typically happens in these cases, offers a few surprises. The scientists who carried out the analyzes of the data received from the Voyager 1 have concluded that the spacecraft has reached interstellar space in August 2012.

In the press conference held yesterday by NASA, it was with understandable emotion that Dr. Ed Stone, who’s been part of the Voyager missions since 1972, announced that the Voyager 1 spacecraft is in the interstellar space. This conclusion was made ​​difficult by the unexpected characteristics of the border region of the solar system, which has forced scientists to rethink some of their theories.

About three years ago, the Voyager 1 spacecraft reached the area called “termination shock” at the edge of the solar system. At that point, scientists expected that sooner or later the direction of the magnetic field changed because the influence of the Sun was no longer enough from the electromagnetic point of view. This hasn’t happened so scientists have focused on the characteristics of the plasma.

Outside the heliosphere, which is the space area in which the solar wind makes its influence felt, the ionized gases are no longer those from the Sun but plasma coming from other stars after a journey lasting even millions of years. Despite the distances covered, the interstellar plasma is denser than the Sun’s.

Measuring the characteristics of the plasma was complicated because now only a few instruments of the Voyager 1 spacecraft still work. The scientists had to use an instrument that was originally secondary for the detection of electromagnetic waves in plasma, on the 10-meter long antennas. A stroke of luck came from a coronal mass ejection that came from the Sun.

The Voyager 1 spacecraft is now about 19 billion kilometers (about 12 billion miles) from the Sun so the coronal mass ejection occurred in march 2012 reached the Voyager 1 only in April 2013. At that point, the plasma surrounding the probe started vibrating like the string of a violin. The oscillation pitch allowed the scientists to determine the density of the plasma, which was found to be more than forty times denses than those found in the outer layers of the heliosphere. It was the density level that was expected in interstellar space.

Now the Voyager 1 space probe is officially in interstellar space but at the same time is still in the solar system. In fact, the Oort cloud, much farther from the Sun than Voyager 1, is considered part of the solar system. In the end it’s a matter of definitions.

The press conference held yesterday by NASA was in Star Trek style. This is appropriate because the mission of the Voyager 1 space probe, like its twin Voyager 2 and many other probes, follows the same spirit of the famous sci-fi saga. But this is science, not science fiction, and Voyager 1 has really gone where no one has gone before.

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