Has Voyager left the solar system?
NASA’s intrepid Voyager 1 space probe has reached a strange, uncharted region at the farthest edges of our solar system, according to three research papers published this week in the journal Science. Although there were signs this past summer that Voyager had entered interstellar space, the new research indicates that the spacecraft has entered a mysterious in-between place where solar particles and deep space particles intermingle. According to researchers, the new region may form a section between the solar system and interstellar space.
Launched by NASA in 1977, Voyager 1 is now more than 11 billion miles (18 billion kilometers) from the sun and may soon be the first human artifact to enter interstellar space. Last August, the space probe transmitted data showing a dramatic reduction in solar particles and a simultaneous increase in high-energy cosmic rays emanating from outer space, indicating that Voyager had probably left the solar system. Other measurements, however, were at odds with that conclusion.
First, the probe has not detected a change in the direction of the magnetic field–a sign that it is still within the heliosheath, the bubble of plasma from the sun that surrounds the solar system. Second, the data showed that the cosmic rays encountered by Voyager were not evenly distributed–a finding that puzzled scientists because cosmic rays, which come from supernova explosions all across the galaxy, ought to disperse uniformly in all directions throughout the universe.
Based on the evidence, the scientists believe that Voyager has entered a new kind of solar environment they are calling the “heliosheath depletion region,” where the sun’s influence is diminished and interstellar particles can enter.
“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, in a statement issued today by NASA.
At this point, scientists can only speculate as to when Voyager 1 will escape the sun’s influence and enter interstellar space, NASA officials said. It could take months or even years for the probe to cross that important celestial threshold.
Originally designed to last only five years, Voyager’s power, which comes from the slow decay of radioactive plutonium, will finally begin to run out in the year 2020. By then, project managers will be forced to shut down the probe’s first instrument due to lack of power and, eventually, the second instrument will be turned off, Stone told Discovery News. By 2025, Voyager will run out of power completely.
Voyager 1’s sister spacecraft Voyager 2, also launched in 1977, is about 9 billion miles (15 billion kilometers) from the sun and still within the heliosphere, according to NASA. So far, indications are that Voyager 2 has not yet encountered the anomalies registered by Voyager 1. According to Stone, the readings picked up in the region where Voyager 1 is located–where the heliosheath and interstellar space connect–may indicate a strictly local phenomenon.