Voyager 1's Glow Glimmers in Interstellar Space
One of the most iconic photographs in spaceflight history is that of Earth, seen from a distance of 4 billion miles by the outward bound Voyager 1 spacecraft. The 1990 "Pale Blue Dot" gave the world a profound realization that everybody from all human history that has ever existed lived on that one tiny speck in the distance, as legendary science communicator Carl Sagan remarked at the time.
Now, 23 years later, a photograph of another "pale blue dot" has been released by NASA the faint signal from Voyager 1′s radio transmitter reaching us from interstellar space after traveling 11.5 billion miles from Earth.
Last week, NASA confirmed that Voyager 1 had officially left the solar system's heliosphere, escaping from the heliopause and entered interstellar space, the first man made object to leave the sun's domain. Therefore, this pale blue radio speck is the first man made radio signal ever to be received from interstellar space.
The image, that was captured by the Very Long Baseline Array (VLBA) on Feb. 21, was released to celebrate Voyager 1 entering the interstellar medium.
According to NASA, the signal being generated by Voyager 1 is very weak. The spacecraft's main radio transmitter generates just 22 watts the approximate radiated power of a refrigerator light bulb.
But to a huge radio array like the VLBA, Voyager 1′s signal is easily detectable as a faint radio glimmer in the darkness of the interstellar ocean.
"They were able to see a blue speck," Suzanne Dodd, Voyager's project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif., said during a news conference Thursday. "And this image represents the Voyager radio signal as seen by the world's most sensitive ground-based telescope. It's just a speck in amongst a sea of darkness."
Voyager: Goodbye Solar System, Hello Interstellar Space
After a 35-year, 13-billion mile journey, NASA's Voyager 1 spacecraft has become the first human-made object to reach interstellar space, new evidence from a team of scientists shows.
On Aug. 25, 2012, Voyager, which was launched in 1977 to study the outer planets, detected a sudden drop in the number of particles trapped in the bubble of space under the sun's influence, the so-called heliosphere, and a corresponding spike in the number of galactic cosmic rays from outside the solar system.
That evidence alone, however, was not enough to convince scientists Voyager had finally reached interstellar space. What they really wanted to know was how much plasma -- ionized molecules and atoms -- was around Voyager, but that measurement was not possible since the spacecraft's plasma detector stopped working more than 30 years ago.
Computer models had long predicted that within the heliosphere, which is filed with the sun's hot breath of solar wind, plasma density would be a small fraction of what exists in cold interstellar space.
But there was another way. Under very special circumstances, Voyager's two 10-meter (33-foot) antennas can detect vibrations in the plasma that scientists can then use to calculate density.
But not very common. It happened nine years ago when Voyager 1 crossed a shockwave, a telltale sign that the solar wind was no longer moving at supersonic speeds.
Another hint of Voyager's whereabouts came in October and November 2012 when the spacecraft's antennas registered the effects of a solar flare. The bevy of particles emitted in the so-called coronal mass ejection traveled for about a year before reaching Voyager.
Conclusive proof came this spring when Voyager detected another solar outburst.
"We were able, for the first time, to measure the density of the plasma, the number of particles per cubic meter," Gurnett said. "As soon as we detected those oscillations, we knew that we were in the interstellar medium."
"The definition of the heliopause is based on the plasma density and they just couldn't measure that. And we, by some good fortune having to do with solar events, finally could do that," he said.
Extrapolating back in time, scientists calculate that Voyager 1 likely crossed into interstellar space back in August 2012, the same time it measured changes in the prevalence of cosmic rays and solar particles.
While one step of Voyager's journey is over, a new expedition is beginning.
"We are now in interstellar space. This is a very exciting new phase of the mission," said lead scientist Edward Stone, with NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"As usual, the most important thing we'll find is probably something that we didn't expect. That's what makes this mission so very special," he said.
The research appears in this week's Science.
It is estimated that Voyager 1′s dwindling power supply generated by three radioisotope thermoelectric generators (RTGs) will only allow for the spacecraft's science instruments to be powered up until 2020 and then by 2030, the mission will go silent and Voyager 1′s faint radio glimmer will be extinguished for good.
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