ArticleSeptember 12th, 2013
Voyager Becomes First Spacecraft to Enter Interstellar SpaceScience
NASA has announced that the Voyager 1 spacecraft, which left Earth in 1977, is now the first man-made object to ever reach interstellar space.
The scientists working on the Voyager 1 mission say the spacecraft entered interstellar space on or around August 25, 2012. They estimate that Voyager 1 is 11 billion miles from Earth, which puts it beyond all of the planets and Pluto.
Voyager 2, which was actually launched about two weeks before Voyager 1, is also traveling towards interstellar space, but is 2 billion miles behind its identical twin.
This development will provide an opportunity for a new type of space exploration, in which scientists will be able to better study space outside of the sun’s influence.
What does it mean to go “interstellar”?
Interstellar space refers to the space in the galaxy that is not occupied by stars, their magnetic fields or their planetary systems.
To get to interstellar space, Voyager 1 had to pass through the heliosphere, a vast bullet-shaped bubble surrounding the sun (see above illustration) that is created by the sun’s own magnetic field, according to NASA.
The heliosphere is filled with charged particles from the sun’s solar winds, a medium that scientists refer to as plasma. Before Voyager 1 broke into interstellar space, it and Voyager 2 were both travelling through the narrowest and outermost part of the heliosphere known as the “heliosheath.”
Less than two months ago, NASA scientists expressed doubt that Voyager had reached interstellar space.
“If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space,” Voyager project scientist Ed Stone told “Science” in late July. “But the team feels Voyager 1 has not yet gotten there because we are still within the domain of the sun’s magnetic field.”
The cosmic ray and energetic particle data refers to readings that Voyagers 1 and 2 send back to Earth. The plasma in the heliosphere and in interstellar space have different densities. When solar flares send ripples through the plasma, causing the particles to vibrate, two antennae on Voyager pick up the frequency and transmit it back to Earth as an audible radio transmission. Every six months, scientists listen to the tone, played back to them on a tape.
When the tone in the recording changed, the scientists knew that Voyager was now traveling through plasma of a different density, indicating that it had broken free of the heliosphere and into interstellar space.
The Voyager spacecraft
When Voyager 1 was first launched, its mission was to photograph Jupiter and Saturn. But when it traveled far beyond these planets, its mission shifted to look for interstellar space. On board both Voyager 1 and 2 are gold plated phonograph records that contain various sounds and images chosen to communicate the diversity of life on Earth to any extraterrestrial life that might find the spacecraft. On each record’s gold aluminum casing are symbols explaining the mission’s origin and how to play the record.
Until Voyager left the heliosphere and the frequency of its transmissions changed, scientists did not know exactly where the boundary between the heliosheath and interstellar space was. At one point, scientists believed that the barrier was just beyond Jupiter.
Now that Voyager has entered interstellar space, it will be able to take the first-ever readings of low-energy cosmic rays.
Although both Voyager crafts have already long outlived their expected lifespans, NASA hopes to be able to continue receiving readings from Voyager for another 12 to 13 years.
For more, read NewsHour science reporter Rebecca Jacobson’s story about Voyager’s entrance to interstellar space.
–Compiled by Allison McCartney and Rebecca Jacobson for NewsHour Extra
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