NASA scientists announced Thursday (September 12) that the Voyager 1 spacecraft officially is the first human-made object to venture into interstellar space.
The 36-year-old probe is about 12 billion miles from our sun.
New and unexpected data indicate Voyager 1 has been traveling for about one year through plasma, or ionized gas, present in the space between stars. Voyager is in a transitional region immediately outside the solar bubble, where some effects from our sun are still evident.
Voyager 1 first detected the increased pressure of interstellar space on the heliosphere, the bubble of charged particles surrounding the sun that reaches far beyond the outer planets, in 2004.
Scientists then ramped up their search for evidence of the spacecraft's interstellar arrival, knowing the data analysis and interpretation could take months or years.
Voyager 1 does not have a working plasma sensor, so scientists needed a different way to measure the spacecraft's plasma environment to make a definitive determination of its location.
A coronal mass ejection, or a massive burst of solar wind and magnetic fields, that erupted from the sun in March 2012 provided scientists the data they needed.
"The sun basically had an eruption in March of 2012 which was fortunately headed in the way of the Voyager and in about 400 days like a tsunami it finally got to where Voyager is, it caused the plasma to react in a way that it could be sensed and we know for the first time we were in the dense plasma of interstellar space, not in the rarer plasma of the outer part of the solar envoy," said Ed Stone, Voyager project scientist.
When this unexpected gift from the sun eventually arrived at Voyager 1's location 13 months later, in April 2013, the plasma around the spacecraft began to vibrate like a violin string.
"It turns out this oscillation frequency is directly related to the plasma density, say the number of particle per cubic meter, and that's a very important quantity to try to distinguish between the interstellar plasma and the solar plasma," said Voyager Plasma Investigation P.I. Don Gurnett, "The interstellar plasma is actually considerably, has considerably higher density than solar plasma so we can detect these waves when an oscillation occurs kind of a like a vibration in the plasma."
Voyager 1 and its twin, Voyager 2, were launched 16 days apart in 1977. Both spacecraft flew by Jupiter and Saturn. Voyager 2 also flew by Uranus and Neptune. Voyager 2, launched before Voyager 1, is the longest continuously operated spacecraft. It is about 9.5 billion miles away from our sun.
Scientists do not know when Voyager 1 will reach the undisturbed part of interstellar space where there is no influence from our sun. They also are not certain when Voyager 2 is expected to cross into interstellar space, but they believe it is not very far behind.
Presented by Adam Justice