Sep 13, 2013 by Sci-News.com
According to a team of scientists reporting online in the journal Science, NASA’s Voyager 1 has indeed left the Solar System and entered interstellar space.
This image shows Voyager 1′s position on the sky when observed by the Very Long Baseline Array on February 21, 2013. The inset shows radio signal from Voyager 1′s transmitter Image credit: Alexandra Angelich / NRAO / AUI / NSF.
Voyager 1 was launched on September 5, 1977. The spacecraft completed flybys of both Jupiter and Saturn and is currently moving outward from the Sun at about 3.5 AU per year.
“On April 9, the Voyager 1 Plasma Wave instrument began detecting locally generated waves, called electron plasma oscillations, at a frequency that corresponds to an electron density about 40 times greater than the density inside the heliosphere – the region of the Sun’s influence,” explained study lead author Dr Don Gurnett of the University of Iowa.
“The increased electron density is very close to the value scientists expected to find in the interstellar medium.
“This is the first solid evidence that Voyager 1 has crossed the heliopause, the boundary between the heliosphere, and interstellar space,” Dr Gurnett said.
NRAO’s Very Long Baseline Array telescope catches a glimpse of the signal from Voyager 1′s transmitter as seen from more than 11 billion miles away. Image credit: NRAO / AUI / NSF.
For several months, the relative position of Voyager 1 has stirred something of a scientific debate because there remains some lingering evidence of the nearby heliosphere beyond the heliopause.
“Even though Voyager 1 has passed into interstellar space, it does not mean that its journey is over,” said second author Dr Bill Kurth, also from the University of Iowa.
“Now that we’re on the outside, we are learning that interstellar space isn’t a bland region. Rather, there are variations in some of Voyager’s measurements that may be due to the nearby presence of the heliosphere. So, our attention is turning from crossing the boundary to understanding what is going on outside.”
At age 36, Voyager 1 is the most distant human-made object at more than 11.6 billion miles from the Sun, or about 125 astronomical units.
NASA’s Voyager 1 spacecraft. Image credit: NASA / JPL-Caltech.
“At that distance it takes more than 17 hours for a radio signal to travel from the spacecraft to one of NASA’s Deep Space Network antennas. The signal strength is so incredibly weak that it takes both a 230-foot and a 110-foot-diameter antenna to receive our highest resolution data,” Dr Gurnett said.
Another team of astronomers using the Very Long Baseline Array and Green Bank Telescope spotted the faint radio glow from Voyager 1.
According to NASA, the team imaged the signal from Voyager 1′s main transmitter after the spacecraft had already passed beyond the edge of the heliosphere, the bubble of charged particles from the Sun that surrounds our Solar System.
Bibliographic information: D. A. Gurnett et al. In Situ Observations of Interstellar Plasma With Voyager 1. Science, published online September 12, 2013; doi: 10.1126/science.1241681
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