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Washington : NASA's Voyager 2 spacecraft, launched in 1977, has detected an increase in cosmic rays coming from outside our solar system, indicating that it is near interstellar space.
Once Voyager 2 has left the outermost layer of the heliosphere – the vast bubble surrounding the Sun and the planets dominated by solar material and magnetic fields – it will become the second human-made object after Voyager 1, to penetrate the interstellar space, NASA said in a statement Friday.
Voyager 2 is a little less than 17.7 billion km from Earth, more than 118 times the distance from Earth to the Sun.
It is the only spacecraft to have visited the four giant outer planets – Jupiter (1979), Saturn (1981), Uranus (198) and Neptune (1989).
Voyager scientists are monitoring the arrival of the probe in the outer limit of the heliosphere, the heliopause.
"We are witnessing a change in the environment around Voyager 2, no doubt," said Ed Stone, Voyager project researcher at NASA's Jet Propulsion Laboratory in Pasadena, California.
Since the end of August, Voyager 2's "Cosmic Ray Subsystem" instrument has measured an increase of about 5% in the cosmic ray rate reaching the spacecraft compared to the beginning of August.
The low energy charged particle instrument of the probe has detected a similar increase in high energy cosmic rays.
"We will learn a lot in the months to come, but we still do not know when we will hit the heliopause, we are not there yet, it is one thing I can say with confidence." "Stone added.
Three other spaceships follow interstellar trajectories. New Horizons approaches an object from the Kuiper Belt to about one billion kilometers from Pluto on January 1, 2019.
The Pioneer 10 and Pioneer 11 probes no longer work, but will eventually travel in interstellar space.
In May 2012, Voyager 1 experienced an increase in the cosmic ray rate similar to that detected by Voyager 2.
"It was about three months before Voyager 1 crossed the heliopause and entered interstellar space," NASA said.
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