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Voyager at the edge of our solar system


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Kiwithrottlejockey
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« on: June 28, 2013, 05:10:28 pm »


From the Los Angeles Times....

Voyager 1's journey to solar system's edge upends theories

The mysterious region 11 billion miles away proves to be even stranger
than previously thought, according to Voyager's latest readings.


By MONTE MORIN | 6:58PM - Thursday, June 27, 2013

Scientists report on Voyager 1's strange findings at the edge of the solar system. — Picture: Associated Press/NASA.
Scientists report on Voyager 1's strange findings at the edge of the solar system. — Picture: Associated Press/NASA.

AS THE Voyager 1 spacecraft speeds toward interstellar space at a rate of almost a million miles a day, the NASA probe is causing scientists to jettison some long-standing theories on the nature of our solar system and life along its cold, dark edge.

In three studies published Thursday in the journal Science, Voyager researchers provided the most detailed view yet of a mysterious region more than 11 billion miles from Earth, where the sun's ferocious solar winds slow to a whisper and pieces of atoms blasted across the galaxy by ancient supernovae drift into the solar system.

The area, which has been dubbed the "magnetic highway", is a newly discovered area of the heliosphere, the vast bubble of magnetism that surrounds the planets and is inflated by gusting solar winds. Like Earth's magnetosphere, which shields us from radioactive solar winds, the heliosphere shields the solar system from many of the cosmic rays that fill interstellar space.

Scientists had long envisioned its outermost layer, the heliosheath, to be a curved, distinct boundary separating the solar system from the rest of the Milky Way. They theorized that once Voyager 1 crossed that threshold, three things would happen: The sun's solar winds would become still; galactic cosmic rays would bombard Voyager from every angle; and the direction of the dominant magnetic field would change significantly because it would be coming from interstellar space, not the sun.

All of those predictions have been turned on their head by Voyager's latest instrument readings.

Although Voyager 1 is equipped with video cameras, they were shut off more than 20 years ago to save power and memory. Instead the craft observes its environment with a fragile, lattice-work antenna that measures magnetic fields as well as a cosmic ray detector and a plasma detector. (Befitting a space probe launched in 1977, the data are stored on an eight-track tape recorder.)

Toward the end of July 2012, Voyager 1's instruments reported that solar winds had suddenly dropped by half, while the strength of the magnetic field almost doubled, according to the studies. Those values then switched back and forth five times before they became fixed on August 25th. Since then, solar winds have all but disappeared, but the direction of the magnetic field has barely budged.

"The jumps indicate multiple crossings of a boundary unlike anything observed previously," a team of Voyager scientists wrote in one of the studies. They labeled the new area the heliosheath depletion region.

Stranger yet, Voyager 1 detected an increase in galactic cosmic rays — but found that at times they were moving in parallel instead of traveling randomly.

"This was conceptually unthinkable for cosmic rays," said Stamatios Krimigis, a solar physicist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and leader of another one of the studies. "There is no cosmic ray physicist I know who ever expected that they would not all be coming equally from all directions."

The confusion hasn't ended there.

One Voyager project scientist reported in March that the spacecraft had entered interstellar space after more than 35 years of travel. The paper by Bill Webber, a professor emeritus of astronomy at New Mexico State University, triggered a media furor in the process.

Scientists including Krimigis and Edward Stone, a Voyager project scientist at Caltech, contended that the probe had not left the solar system. Voyager 1 remained within the sun's zone of magnetic influence, and therefore within the heliosphere, they said.

"We're not free yet," Krimigis said. "This is a new region that we didn't know existed. We have no road map, and we're waiting to see what's going to happen next."

Theorists are struggling to explain the data. Some say the unexpected increase in magnetic strength is the result of spiraling magnetic fields being compressed against the interstellar medium. Others say this is impossible since there is no solar wind to push them against that boundary, and that there must be another explanation.

Len Fisk, a professor of space science at the University of Michigan, described the studies' findings as "a complete surprise." He said Voyager 1's travels were proving to be both puzzling and exciting.

"It's causing a fundamental reconsideration of how the heliosheath interacts with the local interstellar medium," said Fisk, who was not involved in the new analysis.

One of the possible explanations for Voyager's peculiar magnetic readings is that the sun's magnetic fields have combined with the interstellar magnetic field in places — a process called magnetic reconnection.

Such reconnection has been observed between the magnetic fields of the sun and Earth, said Stone, a former director of the Jet Propulsion Laboratory in La Cañada Flintridge. "Maybe that's what's happening here, but we really don't know," he said.

Adding still more mystery is the fact that Voyager 2 has yet to experience anything like its twin. Both spacecraft are headed toward the forward edge of the heliosphere, but are more than 9 billion miles apart.

Although Voyager 1 was launched 16 days after Voyager 2, it followed a more direct route toward the edge of the solar system. Since 1998, when it overtook Pioneer 10, it has been the farthest man-made object from Earth.

Voyager scientists say they're in no position to predict when the probe may finally exit the solar system. It could be months, or it could be years.

"I wouldn't dare to make an estimate," Krimigis said. "Voyager will probably prove us wrong, again."


Related news stories & links:

 • Interactive Graphic: Voyagers are traveling near the edge of the solar system

 • Graphic: The travels of the two Voyager spacecraft

 • Scientists debate whether Voyager 1 has left the solar system

 • Voyager 1 and a poignant farewell to a scientist


http://www.latimes.com/news/science/la-sci-voyager-heliosphere-20130628,0,6860711.story
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Kiwithrottlejockey
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« Reply #1 on: September 14, 2013, 03:08:37 pm »


From the Los Angeles Times....

NASA confirms Voyager 1's historic frontier crossing

After a months-long scientific debate, NASA scientists have concluded
that Voyager 1 last year became the first spacecraft to leave the
solar system's heliosphere and enter interstellar space.


By MONTE MORIN | 6:50PM - Thursday, September 12, 2013

NASA said Thursday that the Voyager 1 probe has become the first human-made object to leave our solar system and enter interstellar space. — Picture: AFP/Getty Images.
NASA said Thursday that the Voyager 1 probe has become the first human-made object to leave our solar system
and enter interstellar space. — Picture: AFP/Getty Images.


AND WE never even got a chance to say goodbye.

After 36 years of space exploration and months of heated argument among scientists, NASA officials confirmed Thursday that Voyager 1 had indeed crossed into interstellar space more than a year ago.

The final piece of evidence that led scientists to conclude the spacecraft had crossed the historic threshold arrived in the form of an other-worldly radio transmission recorded on Voyager's vintage eight-track tape recorder this spring.

"It's the first spacecraft to reach interstellar space," said Ed Stone, a Voyager project scientist at Caltech and former chief of the Jet Propulsion Laboratory in La Cañada Flintridge, where the craft was built. "Think of that. It's really something that's mind-boggling."


Edward C. Stone with a Voyager model in 1972. — Photo: NASA.
Edward C. Stone with a Voyager model in 1972. — Photo: NASA.

Proof of the feat was published Thursday in the journal Science, and focused on two very distinct vibrations that were picked up by Voyager's 30-foot whip antennas.

In what scientists described as a double-stroke of good luck, the antennas were able to convert the density of surrounding space plasma into audio signals — along with the help of two immense and well-timed solar flares.

"We literally jumped out of our seats when we saw the data," said lead study author Don Gurnett, a University of Iowa space physicist and Voyager project scientist. "It was clear that we were in the interstellar medium."

Gurnett and his colleagues concluded that Voyager left the heliosphere — the bubble-shaped region of space dominated by the sun's gusting solar winds — on or around August 25th, 2012. It is now 11.6 billion miles from Earth.

Some scientists have referred to the edge of the heliosphere as the boundary of the solar system. But technically speaking, NASA scientists said the solar system extends out to the Oort Cloud, a distant spherical shell that is believed to be the birthplace of many comets.

Voyager 1, which launched in 1977, will not reach the inner edge of the Oort Cloud for another 300 years, and it could take as long as 30,000 years to exit it, according to NASA.

Scientists have been vigorously debating Voyager's whereabouts since March, when it became clear the probe was being bombarded by an increasing number of galactic cosmic rays while the number of high-energy particles emanating from the sun had plummeted.

Stone and other NASA scientists, however, said they could not be certain Voyager had entered interstellar space until the magnetic fields surrounding the craft had changed direction.

After waiting for that change for more than a year, Stone conceded this week that Voyager had yet again proved scientists wrong.

"It's a big surprise, and it's another mystery," Stone said. "This is not what our models were telling us."




Confusion over Voyager's whereabouts has a lot to do with the failure of a specific piece of equipment known as the plasma science experiment, or PLS. The device, which was developed at the Massachusetts Institute of Technology, measures the electron density of space plasma — ionized gas that is ejected from the sun, as well as from other stars.

Cool plasma, the product of stars that exploded millions of years ago, populates interstellar space. It has a high density of about 100,000 electrons per cubic meter of space, Gurnett said.

Super-heated plasma, like the solar wind that flows from our sun, fills the heliosphere. It is much less dense, with only about 1,000 electrons per cubic meter.

A functioning PLS would have been able to sense the density change as Voyager exited the heliosphere.

"The instrument failed in 1980, so the spacecraft is sort of instrument-challenged," Gurnett said. "That's one of the major failures we've had. There really aren't that many."

Voyager does have two functional plasma wave antennas that stretch from its base and form a wide "V". The antennas detect the vibration of excited plasma particles and convert that motion into an audible ringing that is stored on the eight-track tape.

The frequency of the ring is associated with a specific density of plasma. The higher the frequency, the denser the plasma.

The only trouble is, something has to excite the plasma to get it to "ring" — something like a large solar flare or coronal mass ejection. Waiting for such a solar event can take years. And when it does occur, it can take as long as a year for the shock wave to reach Voyager.

Fortunately for Voyager scientists, the antennas picked up two long-lasting oscillations in the last year — one in October and November 2012 and another in April and May 2013. In both cases, the frequency suggested that the plasma was cold and dense. Voyager was in interstellar space.

"It was key evidence," Stone said. "We really needed to measure plasma to know if we were inside or outside the heliosphere. Everything else is more of a proxy."

Gurnett and his colleagues arrived at the crossing date of August 25th by extrapolation.

Plasma density was increasing in a linear fashion as Voyager moved farther into interstellar space. The frequency measured in the fall of 2012 was 2.2 kilohertz, and by the spring of 2013 it had risen to 2.6 kilohertz.

Previous research told Gurnett that the frequency at the crossing point should be 2 kilohertz. By plotting each point on a line, he was able to arrive at a date.

It's no small coincidence that it was the exact date given in March by Bill Webber, a professor emeritus of astronomy at New Mexico State University. Webber, another Voyager project scientist, was the first to break from the official line and publish a paper suggesting the probe had left the heliosphere. A media frenzy ensued.

Marc Swisdak, a space plasma physicist at the University of Maryland, also argued that Voyager had entered interstellar space more than a year ago. In a study published last month in Astrophysical Journal Letters, he presented a theory to explain why the craft hadn't noticed a change in magnetic fields.

Swisdak, who was not involved in the most recent study, said the new evidence looked "fairly conclusive."

"Density measurement is not quite a smoking gun, but it's pretty close to it," he said. "It's pretty clear that we've crossed some sort of boundary."

Scientists are hoping that many gaps in their understanding will be filled in by Voyager 2. The sister spacecraft, which also launched in 1977, is nearing the edge of the heliosphere via a different path and is expected to encounter interstellar space within the next several years.

Unlike Voyager 1, however, Voyager 2 has a fully functioning plasma science instrument and has been sending back density readings throughout its journey.

"I think it's going to teach us even more," Stone said. "We've entered a new era of exploration."


http://www.latimes.com/science/la-sci-voyager-20130913,0,788709,full.story
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« Reply #2 on: September 14, 2013, 03:08:59 pm »


From the Los Angeles Times....

A postcard from Voyager 1 as it heads for solar system exit

By GEOFFREY MOHAN | 1:58PM - Friday, September 13, 2013

An artist's rendering of Voyager 1's sky position based on signals picked up by radio telescopes. — Image: Alexandra Angelich/NRAO/AUI/NSF.
An artist's rendering of Voyager 1's sky position based on signals picked up by radio telescopes. — Image: Alexandra Angelich/NRAO/AUI/NSF.

YOU CAN'T spot Voyager 1 as it leaves the solar system’s heliosphere, but the National Radio Astronomy Observatory can, and did it just for kicks.

Well maybe not for kicks, but scientists were interested in how well their array of 10 radio telescopes, stretching from Hawaii to St. Croix, Virgin Islands, could plot the spacecraft, which is more than 11 billion miles from Earth. Usually, those instruments home in on the faint radio signals from quasars, black holes and the like. They also routinely track NASA's Cassini spacecraft, out around Saturn.

But in February and again in June, scientists trained the instruments on Voyager 1. At the time, scientists were hotly debating whether the craft, launched in 1977, had burst through the solar winds enveloping our planets and sun.

"It was mainly done to see what the instruments can do," said Walter Brisken, a scientist at the radio observatory based in New Mexico.

At about 22 watts, Voyager 1's main transmitter signal pulses like a police radio, or a refrigerator lightbulb if it were in the visible light spectrum. But that's quite brilliant to the Very Long Baseline Array, and to the steerable, single-dish Green Bank Telescope in West Virginia.

"The signal is extremely strong," Brisken said. "You can detect it in fractions of a second."

Scientists used data from both instruments to plot Voyager on a celestial grid system that's "almost like establishing mile markers on a highway," Brisken explained. It's not the kind of data that would resolve whether the craft left the heliosphere, but it did nail Voyager's position to within fractions of an arc-second of where it had been predicted to be as it soared through space at some 38,000 miles per hour. (An arc-second is roughly the size of a penny viewed from about 2.5 miles away.)

Scientists analyzing a plasma signal from the craft announced Thursday that they believed Voyager 1 had entered interstellar space on August 25th, 2012. For the better part of this year, there had been substantial debate about whether the craft had passed that milestone. NASA now acknowledges that Voyager 1 exited the heliosphere.

But if you are picky about your definition of leaving the solar system — and astronomers tend to be — you could say Voyager 1 has as much as 30,000 years of flight ahead of it before it will pass the Oort Cloud, a distant shell that is believed to be the birthplace of many comets.

Either way, Voyager 1 has at least entered the record books, and sent back a belated postcard to boot.


http://www.latimes.com/science/sciencenow/la-sci-sn-voyager-postcard-20130913,0,2600886.story
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« Reply #3 on: September 14, 2013, 03:09:12 pm »


From the Los Angeles Times....

NASA scientists at JPL, elsewhere reflect on Voyager's journey

By JOSEPH SERNA | 2:50PM - Friday, September 13, 2013

Voyager 1 was built at the Jet Propulsion Laboratory. Today it is in interstellar space, 11.6 billion miles from Earth. — Image: NASA.
Voyager 1 was built at the Jet Propulsion Laboratory. Today it is in interstellar space, 11.6 billion miles from Earth. — Image: NASA.

NOW THAT Voyager 1 has safely reached interstellar space, scientists who have spent decades working on the mission at NASA’s Jet Propulsion Laboratory can finally breathe a sigh of relief.

"We've had 30 years of fear that something could go wrong," said Torrence Johnson, a senior research scientist at JPL who worked on Voyager camera equipment. "There were white-knuckle moments."

Those fears are gone now.

The Voyager 1 probe, first conceived in 1972 and launched in 1977, has exited the sun's heliosphere, considered by many to be the informal boundary of the solar system. It’s the first man-made object to do it.

"We got there," said Ed Stone, a Voyager project scientist at Caltech and former JPL chief. "This is something we hoped for when we started this 40 years ago."

Scientists declared that Voyager had crossed the boundary after tracking the density of plasma surrounding the spacecraft. They got readings that were only possible once Voyager had left the heliosphere, the bubble-shaped region of space dominated by the sun’s gusting solar winds.

"We’re in a truly alien environment," Stone said.

Even as they cheered the accomplishment, the NASA scientists were quick to turn their focus toward the future.

"There is a sense that this is only the beginning," said Gary Zank, director of the Center for Space Plasma and Aeronomic Research at the University of Alabama in Huntsville. Though "we’re out of our solar environment," he said, "we've stepped into the galaxy."

Johnson, 68, was just a twenty-something doing post-doctoral research at MIT when he moved to California in 1968 to work for JPL.

The Caltech grad and Altadena resident said scientists assigned to the mission in its early days were ambitious about what Voyager could accomplish. However, they weren’t always completely upfront about their grand designs when they sold the project to the lawmakers in Washington who controlled NASA’s purse strings.

Voyager would go to Jupiter and maybe Saturn, they said at the time. A mission to those planets was cheaper than one bound for Neptune and beyond. But hey, if the planets happened to align at the right time (they would) and Washington approved additional funds after the mission was underway (they did), Voyager could provide mounds more data about the solar system as the planets' gravity flung it deeper into space.

Though it has crossed a historic threshold, Voyager’s mission is far from over. Its camera was turned off in 1990 and another important tool failed a decade earlier, but there's plenty "the little space craft that could" can still accomplish, said Voyager project manager Suzanne Dodd.

Voyager 1 will continue to operate as-is until 2020. Then, over the next five years, scientists will shut down its instruments one at a time until it’s almost completely dead.

Voyager can continue sending basic engineering data to Earth until 2035, Dodd said.


Listen to the sounds of interstellar space

http://www.latimes.com/science/sciencenow/la-sci-voayger-interstellar-space-jpl-20130912,0,7518205.story
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