Scientists say Voyager I, the spacecraft NASA launched in 1977, is approaching the outer edge of our solar system, and will soon become the first human-made object to reach interstellar space, MSNBC reported.
"It's not that clear because there's no signpost telling you that you're now leaving the solar system, but the evidence is mounting that we're getting really close," Arik Posner, a Voyager program scientist at NASA's headquarters in Washington, DC, told NPR.
Voyager I, now 11 billion miles from Earth, and Voyager II, 2 billion miles behind Voyager I, are still within the heliosphere, the solar plasma and solar magnetic fields that surround the solar system, NPR reported.
However, recent data sent back by Voyager I show that the probe is being bombarded by more galactic cosmic rays than before, suggesting the boundary with interstellar space is approaching, MSNBC reported.
"From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering," Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, said in a statement, according to MSNBC. "More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased 5 percent in a week and 9 percent in a month."
Scientists did not expect the Voyagers to travel this far, Posner told NPR. "But now that they've made it, we are extremely excited to find out what's out there," he said.
It’s estimated that the spacecraft have 10 to 15 years of juice left in their radioactive batteries, NPR reported.
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