NASA's Voyager 1 space probe has reached the boundary of the solar system, an uncharted region before interstellar space.
The strange zone that is just within the sun's "bubble" is said to be where solar particles and deep space particles intermingle (see image). It is about 11 billion miles from Earth - further away than Pluto.
“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” said Ed Stone, of the California Institute of Technology in Pasadena, in a NASA statement.
News of the probe's journey was published in three papers in the journal Science on Thursday.
Astronomers report that the probe has reached the ‘heliosheath depletion region.' Outside this region is the wider galaxy, where the sun has no influence.
The goal is to push the Voyager outside our solar system for more data about regions unknown to astronomers.
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To know when the probe has crossed into interstellar space, astronomers are looking at measures such as cosmic rays, a decrease in stellar particles and a change in the magnetic field.
Though the first two have changed, the last has yet to change, implying that the probe has not broken through the heliosheath.
The Voyager 1 and 2 were launched in 1977 and have been flying through space ever since. Though initially tasked with exploring Jupiter and Saturn, they were then sent even further.
They are said to have discovered Jupiter's volcanoes and more details about Saturn's rings.
Voyager 2 is the only probe to have ever reached Uranus and Neptune. Now the Voyager 1 may become the only human-made object to ever break into interstellar space.