Voyager 1's Glow Glimmers in Interstellar Space

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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Voyager 1 and 2: Spacecraft Twins

 

NASA

In 1977, NASA sent the Voyager spacecraft to visit the gas giants Jupiter and Saturn. And though they're twins, the two spacecraft followed very different trajectories: Voyager 1 left the plane of the solar system after flying by Saturn on a path towards the edge of the heliosphere while Voyager 2 stayed in line with the planets to visit the outer ice giants Uranus and Neptune.

More than 30 years later, it's Voyager 1 that's in the news all the time since it is well on its way to becoming our first true interstellar spacecraft. But today, on the 32nd anniversary of Voyager 2's launch (Aug. 20, 1977), it's time to look back at some of the amazing sights it saw during its planetary flybys.

We might not think about it much, but as the only spacecraft to see the two furthest planets up close, the breathtaking images we have of Uranus and Neptune are all thanks to Voyager 2.

NASA

Though the second of the pair by numerical designation, Voyager 2 was actually the first spacecraft to launch. It left Cape Canaveral on a Titan IIIE rocket on Aug. 20, 1977; Voyager 1 launched on Sept. 5, 1977. It was the first to launch, but Voyager 2 followed a slower trajectory that would see it encounter Jupiter months after Voyager 1.

NASA

Voyager 1 started imaging Jupiter in the January of 1979, and after taking some 19,000 pictures in four months, it passed the baton to Voyager 2 in April. The second interplanetary spacecraft added another 14,000 images to the Jupiter image file, making its closest approach to the planet on July 9.

 

NASA

Jupiter wasn't an unknown entity when the Voyager spacecraft arrived; astronomers had been studying it from the Earth for centuries. But what the two spacecraft found surprised scientists -- the physical, geologic, and atmospheric processes that have shaped the planet and its system of satellites. Most notably, the active volcanoes on the Galilean moon Io. It was totally unexpected to find volcanic activity on a moon, and the more scientists studied of Io's volcanism the more interesting it became. The moon's volcanic eruptions seem to be the primary source of material in Jupiter's magnetosphere.

NASA

Before leaving the Jovian system, Voyager 2 took a series of pictures of the Galilean moon Ganymede, which mission scientists have stitched into this mosaic. Ganymede is the largest satellite in our solar system, larger even than Mercury, meaning if it were to orbit the sun and not Jupiter it would easily be classified as a planet. And it would be an ice world. On top of the moon's metallic iron core (that generated a magnetic field) and the layer of rock is a thick shell of ice that might contain some amount of rocky material. In 1996, astronomers found evidence of a thin oxygen atmosphere on Ganymede using the Hubble Space Telescope.

 

NASA

Voyager 2 reached Saturn two years after its close encounter with Jupiter, and it imaged the ringed planet with more sensitive cameras than Voyager 1. It saw elongated ovals in Saturn's atmosphere, tilted features in the east-west shear zones, and other features that were on the whole similar to those seen on Jupiter but smaller and more subdued. Some of Saturn's atmospheric variations can be seen in this image that combines the view through ultraviolet, violet, and green filters.

NASA

As it approached the ringed planet, Voyager 2 saw Saturn and its moons Tethys, Dione, and Rhea together (though this picture was stitched together from individual frames). The spacecraft, at this point, was 13 million miles from Saturn, and the black dot in planet's southern hemisphere is the shadow cast by Tethys.

 

NASA

Voyager 2 also caught this view of Saturn's moon Titan. It might not look like much, but the white glow is Titan's thick atmosphere. It's clearly visible around the whole of the moon, particularly in the upper left. At the time, the spacecraft was a little over 620,000 miles away on Aug. 25, 1981.

NASA

On Jan. 24, 1986, Voyager 2 became the first spacecraft in history to visit Uranus. At its closest pass, the spacecraft came within 50,600 miles of the planet's cloudy upper layer. While flying by the planet, Voyager 2 managed to image ten previously unseen moons and Uranus' ring system in fine detail. Data gathered during the flyby revealed the planet's rate of rotation is about 17 hours and 14 minutes, that it has a significant magnetic field, and that the global temperature is generally fairly consistent even though Uranus' equatorial region gets less sunlight than its poles.

 

NASA

In studying Uranus' moons, Voyager 2 found complex surfaces indicative of a varied geologic past. This detailed view of the Miranda shows at least three types of terrain of different ages and geologic styles. To the left is an ancient hilly region that has been cratered over time. Towards the center of the image is a deeply grooved terrain with linear valleys and ridges. On the right along the terminator is a complex terrain with irregular ridges and few craters.

NASA

As Voyager 2 left Uranus, it caught this stunning shot of the planet as a slim crescent against the black backdrop of space.

 

NASA

Perhaps the most recognizable picture of Neptune, this picture of the planet's full disk was stitched together from images taken on Aug. 16 and 17, 1989. Within two weeks, the spacecraft would make its closest flyby not only of Neptune but of any planet it visited. Voyager 2 passed within 3,000 miles of Neptune's north pole on Aug. 25, 1989 before beginning its journey to the edge of our solar system.

NASA

Voyager 2 caught this stunning view of Neptune and its moon Triton three and a half days after making its close flyby of the planet. Triton is Neptune's largest moon and the only moon in our solar system that orbits in the opposite direction that its host planet rotates. This uncommon orbit combined with its icy composition has led some scientists to suspect that Triton was an independent body that was captured by Neptune's much stronger gravity. When it took this picture, Voyager 2 was about 3 million miles from Neptune.

NASA

Three hours before its closest approach, Voyager 2 caught this close view of linear clouds near Neptune's eastern terminator. The light and shadow shows that these clouds are raised above Neptune's already thick cloudy surface. Voyager 2 took this picture from about 98,000 miles away. Scientists figured that the cloud streaks are 31 to 124 miles long, 18 to 31 miles wide, and as tall as 31 miles.

 

 

 

 

 

 

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