In the late ’70s and early ’80s, the two NASA’s Voyager spacecrafts had been in the spotlight for the extraordinary photos they took of Jupiter, Saturn and a number of their satellites. In later years, they had gradually fallen into oblivion but despite their progressive problems with power supply they kept on sending data and a couple of years ago scientists started to taking an interest in particular to Voyager 1 because it was approaching the edge of the solar system.

NASA’s scientists tried to figure out where was the boundary of the heliosphere, the region of space where the density of the solar wind is greater than that of interstellar matter, and expected the Voyager 1 to need about four more years to get there.

On 28 July 2012, the Voyager 1 detected that the levels of high-energy cosmic rays originated outside the solar system had suddenly increased by 5% and within a few hours the levels of low-energy particles coming from the inner solar system were halved. After three days, however, the levels went back to values close to the previous ones.

Both Voyager space probes had already detected anomalies in the magnetic fields at the edge of the solar system and scientists now speculate that in that area there’s a sort of foam of magnetic bubbles that twist in various ways. The data the Voyager spacecrafts keep on sending are unique and interesting to understand how cosmic rays are trapped in those bubbles.

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Beyond the individual events, the Voyager 1 found that on average the particles from the Sun are less and less while cosmic rays increase. Those are two criteria that suggest that the spacecraft has reached interstellar space a few weeks ago.

A third criterion is the direction of the magnetic field. Scientists are analyzing the data to see if it has changed direction and the announcement of the results is expected to determine whether the Voyager 1 spacecraft really got out of the solar system.

Meanwhile, last month there were celebrations for the thirty-fifth anniversary of the Voyager 1 launch and last week representatives of the Voyager mission received the Breakthrough Award from the magazine “Popular Mechanics”, given to projects that lead to major advances in technological disciplines, space exploration and other fields. Perhaps the Voyager 1 has left the solar system or it might take a little more for it to reach interstellar space but certainly together with its twin Voyager 2 it represents a milestone of space missions.