41-year old NASA probe may be near interstellar space
Once Voyager 2 exits the outermost layer of the heliosphere -- the vast bubble around the Sun and the planets dominated by solar material and magnetic fields -- it will become the second human-made object after Voyager 1 to enter interstellar space NASA said in a statement on Friday.
Voyager 2 is little less than 17.7 billion km away from Earth -- or more than 118 times the distance from Earth to the Sun.
It is the only spacecraft to visit all four giant outer planet -- Jupiter (1979) Saturn (1981) Uranus (198 ) and Neptune (1989).
Voyager scientists have been watching for the spacecraft to reach the outer boundary of the heliosphere known as the heliopause.
"We re seeing a change in the environment around Voyager 2 there s no doubt about that " said Voyager Project Scientist Ed Stone from NASA s Jet Propulsion Laboratory in Pasadena California.
Since late August the "Cosmic Ray Subsystem" instrument on Voyager 2 has measured about a five percent increase in the rate of cosmic rays hitting the spacecraft compared to early August.
The probe s Low-Energy Charged Particle instrument has detected a similar increase in higher-energy cosmic rays.
"We re going to learn a lot in the coming months but we still don t know when we ll reach the heliopause. We re not there yet -- that s one thing I can say with confidence " Stone added.
Three other spacecraft are on interstellar trajectories. New Horizons is closing in on a Kuiper Belt Object more about a billion miles beyond Pluto on January 1 2019.
Pioneer 10 and Pioneer 11 probes are no longer functioning but will eventually travel into interstellar space.
In May 2012 Voyager 1 experienced an increase in the rate of cosmic rays similar to what Voyager 2 is now detecting.
"That was about three months before Voyager 1 crossed the heliopause and entered interstellar space " said NASA.
--IANS na/ksk
