It turns out that sailing through interstellar space isn’t so peaceful.
NASA’s Voyager 1 spacecraft — the only object made by humans to reach interstellar space — might still be caught what scientists have described as a cosmic “tsunami wave,” a shock wave that first hit the probe in February, according to new research. You can hear the eerie interstellar vibrations in a video, courtesy of NASA.
“Most people would have thought the interstellar medium would have been smooth and quiet,” study researcher Don Gurnett, professor of physics at the University of Iowa, and the principal investigator of Voyager 1’s plasma wave instrument, said in a statement from NASA. “But these shock waves seem to be more common than we thought.” [Photo Timeline: Voyager 1 in Interstellar Space]
Such a shock wave was what helped scientists determine that Voyager 1, which launched in 1977 on a “grand tour” of the outer planets, had officially left the solar system.
Last year, researchers keeping tabs on the car-sized spacecraft (12 billion miles away) analyzed measurements the Voyager 1 made in the aftermath of a powerful eruption from the sun known as a coronal mass ejection, or CME. This solar blast occurred in March 2012 and hit Voyager 1 from April to May 2013. The shock wave caused the particles around the spacecraft to vibrate substantially. Based on the frequency of these vibrations, scientists could measure the density of the probe’s surroundings.
The density of the particles around Voyager 1 was 40 times higher than scientists had previously observed when the space probe was still in the outer layers of the heliosphere, the giant bubble of charged particles and magnetic fields that surrounds the sun and the planets in our solar system. Voyager 1 team members concluded that the spacecraft had exited the heliosphere and entered a new cosmic realm. After researchers went back and looked at old data, they concluded that Voyager 1 crossed into interstellar space on August 25, 2012.
Voyager 1 detected its third and most recent interstellar shock wave in February. The vibrations were still going on as of November data, according to NASA. That’s remarkable considering that over the course of this event, the spacecraft has traveled 250 million miles (400 million kilometers).
The researchers say they are not sure how fast the wave is moving or how big a region it covers. And they’re still trying to understand what they can learn from these waves.
“The density of the plasma is higher the farther Voyager goes,” Ed Stone, project scientist for the Voyager mission from the California Institute of Technology, said in a statement from NASA. “Is that because the interstellar medium is denser as Voyager moves away from the heliosphere, or is it from the shock wave itself? We don’t know yet.”
Scientists used radio telescopes like the Atacama Large Millimeter/submillimeter Array — a vast array of receivers in Chile — used to probe galaxies within 40 million to 600 million light-years from Earth. After observing dozens of merging galaxies, astrophysics found that many galactic collisions will create disc galaxies similar to the Milky Way, a surprising finding.
Their observations of carbon monoxide in 37 colliding galaxies showed pancake-shaped zones of molecular gas, similar to the shape that disc galaxies — which include spiral galaxies and lenticular galaxies — would assume.
“This is a large and unexpected step towards understanding the mystery of the birth of disc galaxies,” lead researcher on the study Junko Ueda, a postdoctoral fellow at the Japan Society for the Promotion of Science, said in a European Southern Observatory statement.
Before, astronomers thought that only elliptical galaxies could arise from mergers. Simulations from the 1970s, however, concluded that elliptical galaxies should be the most popular type of galaxy in the universe. Yet these odd-shaped entities comprise less than 30 percent of galaxies. The new study could help explain why scientists see so many spiral galaxies like the Milky Way in the universe, according to ESO.
The astronomers’ work is the biggest molecular gas study so far, but they said they plan more work to follow up on their research. Astronomers emphasized more observations of older galaxies are required to see if mergers behaved similarly in the young universe.
“We have to start focusing on the formation of stars in these gas discs. Furthermore, we need to look farther out in the more distant universe,” Ueda said. “We know that the majority of galaxies in the more distant universe also have discs. We, however do not yet know whether galaxy mergers are also responsible for these, or whether they are formed by cold gas gradually falling into the galaxy. Maybe we have found a general mechanism that applies throughout the history of the universe.”
The research was published in the Astrophysical Journal Supplement.
A new cosmic map is giving scientists an unprecedented look at the boundaries for the giant supercluster that is home to Earth’s own Milky Way galaxy and many others. Scientists even have a name for the colossal galactic group: Laniakea, Hawaiian for “immeasurable heaven.”
The scientists responsible for the new 3D map suggest that the newfound Laniakea supercluster of galaxies may even be part of a still-larger structure they have not fully defined yet.
“We live in something called ‘the cosmic web,’ where galaxies are connected in tendrils separated by giant voids,” said lead study author Brent Tully, an astronomer at the University of Hawaii at Honolulu.
Galactic structures in space
Galaxies are not spread randomly throughout the universe. Instead, they clump in groups, such as the one Earth is in, the Local Group, which contains dozens of galaxies. In turn, these groups are part of massive clusters made up of hundreds of galaxies, all interconnected in a web of filaments in which galaxies are strung like pearls. The colossalstructures known as superclusters form at the intersections of filaments.
The giant structures making up the universe often have unclear boundaries. To better define these structures, astronomers examined Cosmicflows-2, the largest-ever catalog of the motions of galaxies, reasoning that each galaxy belongs to the structure whose gravity is making it flow toward.
“We have a new way of defining large-scale structures from the velocities of galaxies rather than just looking at their distribution in the sky,” Tully said.
Laniakea, our home in the universe
The new 3D map developed by Tully and colleagues shows that the Milky Way galaxy resides in the outskirts of the Laniakea Supercluster, which is about 520 million light-years wide. The supercluster is made up of about 100,000 galaxies with a total mass about 100 million billion times that of the sun.
The name Laniakea was suggested by Nawa’a Napoleon, who teaches Hawaiian language at Kapiolani Community College in Hawaii. The name is meant to honor Polynesian navigators who used their knowledge of the heavens to make long voyages across the immensity of the Pacific Ocean.
“We live in the Local Group, which is part of the Local Sheet next to the Local Void — we wanted to come up with something a little more exciting than ‘Local,'” Tully told Space.com.
This supercluster also includes the Virgo cluster and Norma-Hydra-Centaurus, otherwise known as the Great Attractor. These new findings help clear up the role of the Great Attractor, which is a problem that has kept astronomers busy for 30 years. Within the Laniakea Supercluster, the motions of galaxies are directed inward, as water flows in descending paths down a valley, and the Great Attractor acts like a large flat-bottomed gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster.
Tully noted Laniakea could be part of an even larger structure.
“We probably need to measure to another factor of three in distance to explain our local motion,” Tully said. “We might find that we have to come up with another name for something larger than we’re a part of — we’re entertaining that as a real possibility.”
The solar system coalesced from a huge cloud of dust and gas that was isolated from the rest of the Milky Way galaxy for up to 30 million years before the sun’s birth nearly 4.6 billion years ago, a new study published online today (Aug. 7) in the journal Science suggests. This cloud spawned perhaps tens of thousands of other stars as well, researchers said.
If further work confirms these findings, “we will have the proof that planetary systems can survive very well early interactions with many stellar siblings,” said lead author Maria Lugaro, of Monash University in Australia.
“In general, becoming more intimate with the stellar nursery where the sun was born can help us [set] the sun within the context of the other billions of stars that are born in our galaxy, and the solar system within the context of the large family of extrasolar planetary systems that are currently being discovered,” Lugaro told Space.com via email.
A star is born
Radiometric dating of meteorites has given scientists a precise age for the solar system — 4.57 billion years, give or take a few hundred thousand years. (The sun formed first, and the planets then coalesced from the disk of leftover material orbiting our star.)
But Lugaro and her colleagues wanted to go back even further in time, to better understand how and when the solar system started taking shape.
This can be done by estimating the isotope abundances of certain radioactive elements known to be present throughout the Milky Way when the solar system was forming, and then comparing those abundances to the ones seen in ancient meteorites. (Isotopes are versions of an element that have different numbers of neutrons in their atomic nuclei.)
Because radioactive materials decay from one isotope to another at precise rates, this information allows researchers to determine when the cloud that formed the solar system segregated out from the greater galaxy — that is, when it ceased absorbing newly produced material from the interstellar medium.
Estimating radioisotope abudances throughout the Milky Way long ago is a tall order and involves complex computer modeling of how stars evolve, generate heavy elements in their interiors and eventually eject these materials into space, Lugaro said.
But she and her team made a key breakthrough, coming up with a better understanding of the nuclear structure of one radioisotope known as hafnium-181. This advance led the researchers to a much improved picture of how hafnium-182 — a different isotope whose abundances in the early solar system are well known — is created inside stars.
“I think our main advantage has been to be a team of experts in different fields: stellar astrophysics, nuclear physics, and meteoritic and planetary science so we have managed to exchange information effectively,” Lugaro said.
A long-lasting stellar nursery
The team’s calculations suggest that the solar system’s raw materials were isolated for a long time before the sun formed — perhaps as long as 30 million years.
“Considering that it took less than 100 million years for the terrestrial planets to form, this incubation time seems astonishingly long,” Martin Bizzarro, of the University of Copenhagen in Denmark, wrote in an accompanying “Perspectives” piece in the same issue of Science.
Bizzarro, like Lugaro, thinks the new results could have application far beyond our neck of the cosmic woods.
“With the anticipated discovery of Earthlike planets in habitable zones, the development of a unified model for the formation and evolution of our solar system is timely,” Bizarro wrote. “The study of Lugaro et al. nicely illustrates that the integration of astrophysics, astronomy and cosmochemistry is the quickest route toward this challenging goal.”
The researchers plan to investigate other heavy radioactive elements to confirm and refine their timing estimates, Lugaro said.
The abstract of the new study can be found here, while this link leads to the abstract of Bizzarro’s companion piece.
A new test could determine once and for all whether NASA’s Voyager 1 probe has indeed entered interstellar space, some researchers say.
While mission team members declared last year that Voyager 1 reached interstellar space in August 2012, not all scientists are sold. Two researchers working with Voyager 1 have drawn up a test to show whether the spacecraft is inside or outside of the heliosphere — the bubble of solar particles and magnetic fields that the sun puffs around itself.
The scientists who came up with the test predict that Voyager 1 will cross the current sheet — a huge surface within the heliosphere — at some point within the next one to two years. When that happens, Voyager team members should see a reversal in the magnetic field surrounding the probe, proving that it is still within the heliosphere. If this change doesn’t occur in the next two years or so, then Voyager is almost certainly already in interstellar space, researchers said.
“The proof is in the pudding,” George Gloeckler of the University of Michigan, lead author of the new study detailing the test, said in a statement. “This controversy will continue until it is resolved by measurements.”
Scientists have recently made measurements that seem to bolster the belief that Voyager is in interstellar space. Researchers measuring data from a solar eruption that shook the particles around Voyager 1 found that the density of the probe’s surroundings was much higher than earlier measurements, when it was thought to be inside the heliosphere.
Because of this difference, some team members have come to the conclusion that Voyager 1 is, in fact, outside of the heliosphere. (While particle densities are higher in the inner solar system than they are in interstellar space, this is not the case at the extreme outer reaches of the heliosphere, scientists said.)
Voyager 1 has measured cosmic rays and other signs indicating that it may have passed into interstellar space, it still hasn’t detected the predicted magnetic field change, Gloeckler pointed out. He expects that the polarity reversal may happen in 2015.
“If that happens, I think if anyone still believes Voyager 1 is in the interstellar medium, they will really have something to explain,” Gloeckler said in the statement. “It is a signature that can’t be missed.”
The developers of the new test think Voyager 1 is moving faster than the solar wind, meaning that it will cross over parts of the current sheet where the magnetic field reversal will happen. This data could prove that the probe is inside the heliosphere, according to a statement from the University of Michigan and the American Geophysical Union.
Other scientists working with Voyager also welcome the test.
“It is the nature of the scientific process that alternative theories are developed in order to account for new observations,” Ed Stone, NASA’s Voyager project scientist, said in a statement. “This paper differs from other models of the solar wind and the heliosphere and is among the new models that the Voyager team will be studying as more data are acquired by Voyager.”
Voyager 1 and its twin Voyager 2 launched to space in 1977 to study the planets of the solar system. Voyager 2 is still in communication with Earth and is expected to continue on, potentially entering into interstellar space a few years from now.
The new test, detailed in a study by Gloeckler and his co-author Len Fisk of the University of Michigan, has been accepted for publication in the journal Geophysical Research Letters.
New data collected by NASA’s Voyager 1 spacecraft have helped scientists confirm that the far-flung probe is indeed cruising through interstellar space, the researchers say.
Voyager 1 made headlines around the world last year when mission scientists announced that the probe had apparently left the heliosphere — the huge bubble of charged particles and magnetic fields surrounding the sun — in August 2012.
They came to this conclusion after analyzing measurements Voyager 1 made in the wake of a powerful solar eruption known as a coronal mass ejection, or CME. The shock wave from this CME caused the particles around Voyager 1 to vibrate substantially, allowing mission scientists to calculate the density of the probe’s surroundings (because denser plasma oscillates faster.) [Photo Timeline: Voyager 1’s Trek to Interstellar Space]
This density was much higher than that observed in the outer layers of the heliosphere, allowing team members to conclude that Voyager 1 had entered a new cosmic realm. (Interstellar space is emptier than areas near Earth, but the solar system thins out dramatically near the heliosphere’s edge.)
The CME in question erupted in March 2012, and its shock wave reached Voyager 1 in April 2013. After these data came in, the team dug up another, much smaller CME-shock event from late 2012 that had initially gone unnoticed. By combining these separate measurements with knowledge of Voyager 1’s cruising speed, the researchers were able to trace the probe’s entry into interstellar space to August 2012.
And now mission scientists have confirmation, in the form of data from a third CME shock, which Voyager 1 observed in March of this year, NASA officials announced Monday (July 7).
“We’re excited to analyze these new data,” Don Gurnett of the University of Iowa, the principal investigator of Voyager 1’s plasma wave instrument, said in a statement. “So far, we can say that it confirms we are in interstellar space.”
Interstellar space begins where the heliosphere ends. But by some measures, Voyager 1 remains inside the solar system, which is surrounded by a shell of comets known as the Oort Cloud.
While it’s unclear exactly how far away from Earth the Oort Cloud lies, Voyager 1 won’t get there for quite a while. NASA scientists have estimated that Voyager 1 will emerge from the Oort Cloud in 14,000 to 28,000 years.
The craft launched in September 1977, about two weeks after its twin, Voyager 2. The probes embarked upon a “grand tour” of the outer solar system, giving the world some its first good looks at Jupiter, Saturn, Uranus, Neptune and the moons of these planets.
Like Voyager 1, Voyager 2 is still active and operational. It took a different route through the solar system and is expected to follow its twin into interstellar space a few years from now.
NASA’s Voyager 1 and Voyager 2 spacecraft are still going strong after nearly 37 years in space.
“Both spacecraft are still operating, still very healthy. I guess as healthy as we are at the table right now,” Suzanne Dodd, the Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL) said, drawing a big laugh from the audience at the SpaceFest VI conference in Pasadena, California, on May 11.
Dodd was fresh out of college in 1985 when JPL recruited her as it geared up for Voyager 2’s upcoming encounter with Uranus. Nearly 30 years later, she is project manager of the Voyager Interstellar Mission under which the two spacecraft continue to explore the vast expanse of space beyond the planets.
Voyagers of the solar system
Dodd was actually the youngster on the Voyager reunion panel. She was joined by Voyager Project Scientist Ed Stone and retired Voyager Mission Design Manager Charley Kohlhase, who were both on the project when it was in the planning stages in the early 1970s.
When the Voyagers were launched in 1977, NASA expected them to last four or five years, long enough to get them through close encounters with Jupiter and Saturn. But, they just kept going and going.
Voyager 2 went on to flybys of Uranus in 1986 and Neptune in 1989. It is now about 105 astronomical units from Earth. (One AU is the average distance between the Earth and sun, about 92 million miles.) Voyager 1, which flew out of the plane of the solar system after its 1980 flyby of Saturn, is in interstellar space at 127 AUs.
Stone and Kohlhase recalled their astonishment when an image showing two exploding volcanoes on Jupiter’s moon Io came into JPL late on a Friday afternoon in March 1979. The plumes went hundreds of miles above the surface, and the fallout covered an area the size of France.
“We had what I call a terracentric view, which was based on understanding Earth,” Stone said. “Before Voyager, the only known active volcanoes in the solar system were on Earth. Then we flew by Io, a little moon about the size of our moon, with 10 times the volcanic activity of Earth. And suddenly our terracentric extrapolation just was falling way short, and that was happening time after time after time.
“It was an incredible time where every day there were so many things we were discovering that we just moved on to the next one,” Stone added. “If we didn’t understand what we were seeing right away, we said, all right, let’s wait ’til tomorrow to see what else we get.”
A groundbreaking mission
The Voyager missions also forever changed the way spacecraft were built and operated.
“The key thing about Voyager that was a revolution was it was a totally computer-controlled spacecraft that flies itself and has fault protection on board so that if something goes wrong, it takes action,” he said. “Because now it takes us 17 and a half hours to get a command up there, and it’s 17 and a half hours before we know if anything has happened.” Before the spacecraft were launched, Kohlhase had the job of sorting through some 10,000 trajectories for projected launch windows in 1976 through 1978. He used computers to determine which ones would allow the spacecraft to make the best approaches to Jupiter, Saturn and their moons. Kohlhase and the scientists settled on 110 trajectories and ultimately used two of them.
Dodd says the Voyager mission continues to throw up challenges today. The spacecraft have 20-watt transmitters – the equivalent of a refrigerator light bulb – and signals are only 1 billionth of a billionth of a watt in strength by the time they reach Earth. JPL uses the powerful antennas of the Deep Space Network to communicate with the distant spacecraft.
“The engineering challenges are extremely unique to Voyager,” Dodd said. “You’re operating instruments below temperatures that we can’t even measure. Challenges of finding out if we turn on a component that’s next to a hydrazine line, would that hydrazine line freeze or not. We don’t know.
“Another unique challenge to it is that the engineers who built this are retired, some have passed away, you need to get people like Charley out of retirement to come and talk to us,” Dodd added. “It’s a challenge engineering-wise, it’s a challenge from a knowledge standpoint of what people know. And that’s what makes this project fun.”
The Voyagers still have a lot of life left in them even after nearly four decades on space.
“Looking forward, we expect to get 10 more years of scientific data out of the Voyager spacecraft,” Dodd said. “We basically turned off everything we can turn off to save power. Backup heaters are off, backup systems are off. We’re having some serious discussions about how to move forward, because we’re almost down to the scientific instruments now.”
After that, the spacecraft could continue on for another five to seven years sending engineering signals to Earth. Engineers are already in discussions with the Deep Space Network about what experiments could be conducted with those signals before the spacecraft fall silent.
By analyzing photos taken by the Hubble Space Telescope, scientists at the SETI Institute in Mountain View, Calif., have caught sight of Naiad, the innermost of Neptune’s moons. The 62-mile-wide (100 kilometers) moon has remained unseen since the cameras on NASA’s Voyager 2 spacecraft discovered it in 1989.
Scientists recently tracked Naiad across a series of eight archival images taken by Hubble in December 2004 after using a different technique to help cancel out Neptune’s glare. Neptune is 2 million times brighter than Naiad, so Naiad is difficult to see from Earth, SETI officials said. [See photos of Neptune, the mysterious blue planet]
“Naiad has been an elusive target ever since Voyager left the Neptune system,” SETI scientist Mark Showalter said in a statement. Showalter announced the new findings today (Oct. 8) during a session at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences, held in Denver.
Now that scientists have spotted the small moon again, there are other mysteries to be solved. Naiad seems to have drifted off course: The new observations show that the moon is now ahead of its predicted path in orbit around Neptune, SETI officials said.
Scientists expect that the new trajectory could have something to do with Naiad’s interaction with one of Neptune’s other moons that caused the innermost moon to speed up in its orbit. The exact cause of the moon’s new orbit won’t be known until researchers collect more data.
The images taken in 2004 also reveal something about the ring arcs surrounding Neptune. Voyager observed four arcs during its flyby of the system, but the newly processed images show that the two leading arcs are absent, while the two trailing arcs haven’t changed, SETI officials said. Scientists aren’t sure what is causing this change, but the arcs have been shifting since their discovery.
“It is always exciting to find new results in old data,” Showalter said. “We keep discovering new ways to push the limit of what information can be gleaned from Hubble’s vast collection of planetary images.”
The same images taken by Hubble also helped Showalter and his colleagues find another small moon orbiting Neptune — a discovery they announced in July. The newfound moon, called S/2004 N 1, is much smaller than Naiad, at 12 miles (20 km) across, but it was easier to spot in the images because its orbit takes it farther from Neptune than Naiad’s orbit takes it from the planet, SETI officials said.
S/2004 N 1 evaded Voyager 2’s cameras in 1989 because of its tiny size. During its flyby, Voyager revealed six previously unknown moons circling Neptune. Scientists have now discovered 14 moons in orbit around the blue planet.
NASA’s Voyager 1 probe won’t rest on its laurels after becoming the first manmade object ever to reach interstellar space.
Voyager 1 arrived in interstellar space in August 2012 after 35 years of spaceflight, researchers announced Thursday (Sept. 12). While this milestone is momentous enough in its own right, it also opens up a new science campaign whose potential already has scientists salivating.
“For the first time, we’re actually going to be able to put our hands in the interstellar medium and ask what it does and what characteristics it possesses,” Gary Zank, director of the Center for Space Plasma and Aeronomic Research at the University of Alabama in Huntsville, told reporters Thursday. “It’s a tremendous opportunity.”
Into the unknown
Voyager 1 and its twin, Voyager 2, launched a few weeks apart in 1977 to study Jupiter, Saturn, Uranus and Neptune, as well as the moons of these outer planets.
The probes completed this historic “grand tour” in 1989, then embarked on a quest to study the outer reaches of the solar system and beyond.
Voyager 1 finally popped free of the heliosphere — the huge bubble of charged particles and magnetic fields that the sun puffs out around itself — on or around Aug. 25, 2012, becoming humanity’s first envoy to the vast realms between the stars.
“This is truly a remarkable achievement,” Zank said. “We’ve exited the material that’s created by the sun, and we’re in a truly alien environment. The material in which Voyager finds itself is not created by the sun; it’s created, in fact, by our neighboring stars, supernova remnants and so forth.”
Many discoveries to come
This new vantage point should yield big scientific dividends, Zank added. For example, Voyager 1 should now help researchers get a much better look at galactic cosmic rays, charged particles accelerated to incredible speeds by far-off supernova explosions.
Observations of galactic cosmic rays made from within the heliosphere are not ideal, since the solar wind tends to affect these high-energy particles substantially.
“Being outside the heliosphere allows us an opportunity to, in a sense, look at the undiluted galactic cosmic ray spectrum,” Zank said. “That will tell us a great deal more about the interstellar medium at very distant locations. It’ll tell us about how the galactic cosmic rays propagate through this very complicated interstellar medium.”
Voyager 1 should also be able to shed light on the nature of the instellar medium, and how material from other stars flows around the heliosphere, researchers said.
“Now we will be able to understand and measure and observe that interaction, which is a very important part of how the sun interacts with what’s around it,” Voyager chief scientist Ed Stone, a physicist at the California Institute of Technology in Pasadena, told SPACE.com.
In short, reaching interstellar space does not mark the end of the road for Voyager 1, which should be able to continue gathering data for a dozen more years as long as nothing too important breaks down. (The probe’s dwindling power supply will force the mission team to turn off the first instrument in 2020, and all of Voyager 1’s science gear will be shut down by 2025.)
“This mission is not over,” said Voyager project manager Suzanne Dodd, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Many, many more discoveries are out there, yet to come.”
NASA’s Voyager 1 spacecraft has encountered a new environment more than 11 billion miles from Earth, suggesting that the venerable probe is on the cusp of leaving the solar system.
The Voyager 1 probe has entered a region of space with a markedly higher flow of charged particles from beyond our solar system, researchers said. Mission scientists suspect this increased flow indicates that the spacecraft — currently 11.1 billion miles (17.8 billion kilometers) from its home planet — may be poised to cross the boundary into interstellar space.
“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, in a statement.
“The latest data indicate that we are clearly in a new region where things are changing more quickly,” Stone added. “It is very exciting. We are approaching the solar system’s frontier.” [Photos From NASA’s Voyager 1 and 2 Probes]
Voyager 1 and its twin, Voyager 2, launched in 1977, tasked chiefly with studying Saturn, Jupiter and the gas giants’ moons. The two spacecraft made many interesting discoveries about these far-flung bodies, and then they just kept going, checking out Uranus and Neptune on their way toward interstellar space.
They’re not quite out of the solar system yet, however. Both are still within a huge bubble called the heliosphere, which is made of solar plasma and solar magnetic fields. This gigantic structure is about three times wider than the orbit of Pluto, researchers have said.
Specifically, the Voyagers are plying the heliosphere’s outer shell, a turbulent region called the heliosheath. But Voyager 1’s new measurements — of fast-moving galactic cosmic rays hurled our way by star explosions — suggest the probe may be nearing the heliosphere’s edge.
“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” Stone said. “More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in a week and nine percent in a month.”
More measurements needed
While it may be tough to identify the moment when Voyager 1 finally pops free into interstellar space, scientists are keeping an eye on the cosmic ray measurements and a few other possible indicators.
One is the intensity of energetic particles generated inside the heliosphere. Voyager 1 has recorded a gradual decline in these particles as it flies farther and farther away from Earth, but it hasn’t seen the dramatic dropoff that scientists expect would accompany an exit from the solar system.
The Voyager team also thinks the magnetic fields surrounding the spacecraft should change when it crosses the solar boundary. Those field lines run roughly east-west within the heliosphere, and researchers predict they’ll shift to a more north-south orientation in interstellar space. They’re currently looking at Voyager 1 data for any signs of such a transition.
In the meantime, both Voyagers just keep on flying and exploring. Voyager 2 trails its twin a little bit; it’s currently 9.1 billion miles (14.7 billion km) from home.
“When the Voyagers launched in 1977, the space age was all of 20 years old,” Stone said. “Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”
The Voyager 1 probe, which is now about 11 billion miles (17.7 billion kilometers) from Earth, has entered an unexpected “transition zone” at the edge of the solar system, according to the study. This finding, along with observations by NASA’s Cassini spacecraft, hints that Voyager may be about to go where no man-made object ever has — into the space between the stars — a few years earlier than previously thought.
“Perhaps by the end of 2012, we will be out in the galaxy,” said the study’s lead author, Stamatios Krimigis, of Johns Hopkins University’s Applied Physics Laboratory. [Photos From NASA’s Voyager 1 and 2 Probes]
Where the solar wind turns a corner
Our sun’s sphere of influence, composed of solar plasma and solar magnetic fields, is called the heliosphere. This gigantic structure is about three times wider than the orbit of Pluto. On the outskirts of the heliosphere lies the heliosheath, a turbulent region at the outer reaches of the solar system.
At the edge of the heliosheath is the heliopause — the demarcation line between our cosmic neighborhood and interstellar space.
Voyager 1, which launched in 1977, is currently plying the heliosheath, as is its twin, Voyager 2. Recently, Voyager 1 stumbled into a part of the heliosheath that scientists didn’t know existed.
In this region, the outward speed of the solar wind — the charged particles streaming from the sun — is essentially zero. Voyager 1’s measurements show it dropping from about 130,000 mph (209,000 kph) in August 2007 down to zero by April 2010. And it hasn’t picked up since.
It’s not that the solar wind has ceased altogether out there; rather, it’s apparently being blown sideways by a powerful interstellar wind, researchers said. This find, first announced at a conference in December, is reported more fully in the new study and backed up with several more months’ worth of data.
The nature and extent of this “transition zone” should come as a surprise to many scientists, who had predicted a relatively sharp boundary between the heliosheath and interstellar space, researchers said.
“It’s at variance with all the theoretical models that anybody has come up with so far,” Krimigis told SPACE.com. “Nobody predicted that we would go through this region of zero velocity, where essentially the solar wind would be sort of sloshing around and not doing anything.”
Leaving the solar system
Krimigis and his colleagues also wanted to figure out just how far Voyager 1 has to go before it reaches interstellar space. So they enlisted the aid of another NASA spacecraft, the Saturn–studying Cassini probe.
The researchers looked at Cassini’s measurements of energetic neutral atoms flowing out of the heliosheath. This information, combined with Voyager 1 observations of charged particles, gave them an idea of how wide the heliosheath is, and by extension where its edge — the heliopause — is located. [Solar System Explained From the Inside Out]
The team calculated that interstellar space likely begins about 11.3 billion miles (18.2 billion km) from Earth. So Voyager 1 appears to be almost there. Since the probe covers about 330 million miles (531 million km) every year, it could pop out of the solar system as early as next year — a surprise, since previous estimates had pegged the probe’s exit at 2015 or so.
That’s not a sure thing, however; the calculation has some uncertainty attached to it. In fact, the heliopause could lie anywhere from about 10 billion to 14 billion miles (16.1 to 22.5 billion km) from Earth, researchers said.
“It could happen any time, but it may be several more years,” said Ed Stone, Voyager project scientist at Caltech in Pasadena, Calif., who was not involved in the new study.
So researchers will doubtless be scrutinizing Voyager 1’s data over the coming months and years, looking for any signs that the probe has officially crossed the heliopause.
“I think we’ll know it when we cross it,” Stone told SPACE.com. “The direction of the [magnetic] field will change when we get out there, and probably its strength as well.”
Another likely sign, Krimigis said, would be a sudden drop in the density of hot particles, which are common in the heliosheath, and higher readings of the colder particles thought to populate interstellar space.
Krimigis and his colleagues report their results tomorrow in the June 16 issue of the journal Nature.
The Voyagers’ instruments are powered by radioisotope thermoelectric generators, which convert the heat emitted by plutonium’s radioactive decay into electricity. The instruments should have enough juice left to keep taking measurements until at least 2020, researchers have said.
Voyagers still truckin’
The main mission of both Voyager 1 and Voyager 2, which is currently about 9 billion miles (14.5 billion km) from Earth, was to study Jupiter, Saturn and their moons.
During the 12 years of their initial planetary mission, the twin probes returned a great deal of data that changed scientists’ understanding of our cosmic backyard, according to Stone.
But when that phase of the mission was over, the Voyagers just kept cruising and contributing. And now, nearly 34 years after their launch, the spacecraft are still delivering key information — this time from the solar system’s edge. Just last week, for example, researchers analyzing Voyager data announced the surprising discovery of huge magnetic bubbles out in the heliosheath.
“Our motto [at first] was ‘Saturn or bust,'” said Krimigis, who has worked on the Voyager mission for four decades. “That was the original objective, to go to Saturn. Everything else was gravy. And now, here we are.”
Courtesy-Space.com by Mike Wall, SPACE.com Senior Writer
The find, made with the help of observations from NASA’s venerable Voyager probes, shakes up prevailing views of the solar system’s outer reaches. And it shows that this region, once thought to be a relatively firm shield against interstellar particles such as galactic cosmic rays, is actually more of a porous membrane.
“We will have to change our view of how the sun interacts with particles, fields and gases from other stars,” Arik Posner, a Voyager program scientist at NASA Headquarters in Washington, D.C., told reporters today (June 9).
Not smooth, but bubbly
Our sun’s sphere of influence, composed of solar plasma and solar magnetic fields, is called the heliosphere. This gigantic structure is about three times wider than the orbit of Pluto. At the edge of the heliosphere lies the heliosheath, a boundary region between the solar system and interstellar space.
For decades, scientists had thought that, in the heliosheath, the sun’s magnetic field curves around in a smooth, consistent arc, forming a relatively uniform structure. [Solar System Explained From the Inside Out]
But that appears not to be the case.
The twin unmanned probes Voyager 1 and Voyager 2, both launched in 1977, are currently plying different parts of the heliosheath, more than 9 billion miles (14.5 billion kilometers) from Earth. And their observations are spurring a rethink of the region. [5 Facts About NASA’s Voyager Spacecraft]
Specifically, the probes measured abrupt changes in the flow of particles, such as electrons, from one patch of space to another.
“What really struck us were the sudden differences between what Voyager 1 was seeing and what Voyager 2 was seeing,” said study co-author James Drake of the University of Maryland. “We had to explain, well, why is that?”
The best explanation, according to subsequent computer models, is that the probes are flying through a frothy field of magnetic bubbles. These bubbles act as particle traps. So particle readings increase while the spacecraft are inside one, then drop when they exit.
These bubbles form as a result of the interaction between the sun’s rotation and its magnetic field. As the sun spins, its magnetic field churns and twists out in the heliosheath. The folded field bunches up on itself, causing lines of magnetic force to crisscross and reconnect, forming the sea of bubbles.
Huge, sausage-shaped bubbles
The sausage-shaped bubbles are gigantic, measuring about 100 million miles (161 million km) across. And there are a lot of them. [Amazing New Sun Photos from Space]
“This entire thing is bubbly, just like the most bubbly parts of your Jacuzzi,” Drake said. He added that an observer flying aboard one of the Voyagers would not be able to see the bubbles, because the gas in the area is too diffuse.
Researchers are confident that this interpretation best fits the Voyager data, though they’d love some more information from newer, more advanced spacecraft as well. So the team is pushing for new missions to further explore this enigmatic region.
“We are pretty confident of this scenario,” said study lead author Merav Opher of Boston University. But, she added, “we need more sensitive instruments with a better suite to really uncover what’s happening. We are just scraping the surface.”
The researchers report their findings in the June 9 issue of the Astrophysical Journal.
A porous shield
Astronomers had imagined that a smooth, laminar heliosheath acted as a pretty stout shield around the solar system, keeping out many fast-moving particles known as galactic cosmic rays.
Cosmic rays are a threat to astronauts, as they can slam into spaceflyers’ cells and damage their DNA. Earth’s atmosphere attenuates cosmic rays, shielding folks on the ground from their worst effects.
However, the sea of bubbles likely acts more like a membrane than a shield, researchers said, potentially letting some of these particles zip through into the inner solar system. But scientists don’t fully understand how the membrane works and just what is able to pass through it.
The bubbles may trap cosmic rays for a while, forcing them to bounce around like pinballs before they finally escape. Figuring out which one of these scenarios is accurate could have a huge bearing on our understanding of the interstellar space environment. If the bubbles are leaky like a sieve, for example, it implies that there may not be as many galactic cosmic rays out there as researchers had thought.
This is just one question of many that astronomers will be tackling now, thanks to the new results.
“We are still trying to wrap our minds around the implications of these findings,” Drake said.
Voyager 1 is now about 11 billion miles (17.7 billion kilometers) from Earth, while Voyager 2 is about 9 billion miles (14.5 billion km) away. Voyager 1 is the most far-flung human-made object in the universe.
Courtesy-Space.com by by Mike Wall, Senior Writer
Scientists made the discovery by using a new computer model, which is based on data from NASA’s twin Voyager probes. The unmanned Voyager 1 and Voyager 2, which launched in 1977, are plying the outer reaches of our solar system, a region known as the heliosheath.
The new discovery suggests that researchers will need to revise their views about the solar system’s edge, NASA officials said. A more detailed picture of this region is key to our understanding of how fast-moving particles known as cosmic rays are spawned, and how they reach near-Earth space.
Cosmic rays are a threat to astronauts, as they can slam into spaceflyers’ cells and damage their DNA. Earth’s atmosphere attenuates cosmic rays, shielding folks on the ground from their worst effects.
NASA hasn’t revealed many details about the new find. The space agency will hold a media teleconference at 1 p.m. EDT on Thursday (June 9) to discuss it in more depth.
Participating in the teleconference are:
— Arik Posner, Voyager program scientist, Heliophysics Division, Science Mission Directorate, NASA Headquarters, Washington, D.C.
— Merav Opher, assistant professor of astronomy, Boston University
— James F. Drake, professor of physics, University of Maryland
— Edward C. Stone, Voyager project scientist, professor of physics, Caltech
— Eugene Parker, professor emeritus of physics, University of Chicago
Voyager 1 is now about 11 billion miles (17.7 billion kilometers) from Earth, while Voyager 2 is about 9 billion miles (14.5 billion km) away. Voyager 1 is the most far-flung human-made object in the universe.
Since this distant light took eons to reach Earth, the map is essentially a window back in time, providing an unprecedented view of what the universe looked like 11 billion years ago. [Top 10 Strangest Things in Space]
Normally, researchers make maps of the universe by looking at galaxies.
“Here, we are looking at intergalactic hydrogen gas, which blocks light,” said researcher Anže Slosar, a physicist at the U.S. Department of Energy’s Brookhaven National Laboratory. “It’s like looking at the moon through clouds — you can see the shapes of the clouds by the moonlight that they block.”
Mapping the universe
Scientists from the Sloan Digital Sky Survey relied on the light of the brightest objects in the cosmos, quasars — brilliantly luminous beacons powered by giant black holes. As light from a quasar voyages to Earth, it illuminates clouds of intergalactic hydrogen gas that absorb light at specific wavelengths depending on the distances between each quasar and these clouds. This leads to an irregular pattern of quasar light known as the “Lyman-alpha forest.”
To make a full three-dimensional map of the universe, the researchers relied on 14,000 quasars. The map reveals a time 11 billion years ago, when the first galaxies were just beginning to come together under the force of gravity to form the first large clusters.
“The most exciting thing for me personally is proving wrong everyone who was telling us that it is never going to work,” Slosar told SPACE.com. The use of the Lyman-alpha forest in creating a 3-D map was unproven, “a large investment of time, 20 percent of a big international project, and it sort of had to work. But we were the first to show that it actually works. So, while we haven’t yet discovered anything amazing about the universe itself using this technique, we demonstrated that it does work and that we will very likely discover new things.”
These observations came from the Baryon Oscillation Spectroscopic Survey (BOSS), the largest of the four projects making up the latest phase of the Sloan Digital Sky Survey. When BOSS completes its observations of about 140,000 more quasars by 2014, astronomers can make a map 10 times larger than the one being released today.
“With that much data, we’re bound to find things that we never expected,” said researcher Patrick Petitjean, a quasar expert at the Institute of Astrophysics of Paris.
Uncovering the mysteries
For instance, the ultimate goal of such maps is to study how the expansion of the universe has changed during its history, which could shed light on the mysterious dark energy that seems to drive the accelerating expansion of the universe.
“Dark energy is one of the most surprising discoveries in physics in the last 20 years,” Slosar noted. “Nobody has a foggiest idea of what it could be. So we study it by studying the expansion history and growth of structure in the universe. To study these we make maps of the universe at different epochs.”
By the time BOSS ends, “we will be able to measure how fast the universe was expanding 11 billion years ago with an accuracy of a couple of percent,” said researcher Patrick McDonald of Lawrence Berkeley and Brookhaven National Laboratories, who pioneered techniques for measuring the universe with the Lyman-alpha forest and helped design the BOSS quasar survey. “Considering that no one has ever measured the cosmic expansion rate so far back in time, that’s a pretty astonishing prospect.”
The scientists could, for example, “discover that dark energy actually kicked in 11 billion years ago rather than 7 billion as predicted by simplest model and that would be just mind-blowing,” Slosar said. “The potential for discovering anomalies is great.”
The scientists detailed their findings May 1 at a meeting of the American Physical Society in Anaheim, Calif.
Courtesy-Space.com by Charles Q. Choi, SPACE.com Contributor
NASA’s twin unmanned Voyager spacecraft, which were launched in 1977, are streaking toward the edge of the solar system at around 37,000 mph (60,000 kph). At that rate, they’ll probably pop out of our sun’s sphere of influence and into interstellar space by 2016 or so, according to mission scientists.
“They are about to break free of the solar system,” Ed Stone, Voyager project scientist at Caltech in Pasadena, Calif., said during a media teleconference yesterday (April 28). “We are trying to get outside of our bubble, into interstellar space, to directly measure what is there.”
A long history of exploration
Voyager 2 was launched on Aug. 20, 1977, and its twin Voyager 1 blasted off a few weeks later, on Sept 5. Both spacecraft were tasked mainly with studying Jupiter, Saturn and their moons. [5 Facts About NASA’s Voyager Spacecraft]
The spacecraft are also carrying so-called “golden records” containing the distilled essences of humanity, such as various musical offerings and greetings to the universe in 55 different languages. The goal is to teach alien civilizations a little about us, should they ever pluck the Voyagers out of the void.
In their early years, the Voyagers made a series of important discoveries about the giant planets. For example, the mission detected active volcanoes on Jupiter’s moon Io – the first time such features were found beyond Earth. The spacecraft also found evidence of a liquid-water ocean beneath the icy surface of Jupiter’s moon Europa.
“Each of these discoveries changed the way we thought of other worlds,” Stone said in a statement.
The Voyagers made it past Saturn, with the spacecraft examining Neptune and Uranus as well. And then they just kept on going, zooming toward the edge of the solar system in different directions and different planes.
Voyager 1 is now about 11 billion miles (17.7 billion kilometers) from Earth, while Voyager 2 is about 9 billion miles (14.5 billion km) away, Stone said. Voyager 1 is the most far-flung human-made object in the universe. [NASA’s 10 Greatest Science Missions]
Probing the heliosheath
While the Voyagers have left the planets well behind, they’re not beyond the solar system yet. They’re still within a huge bubble called the heliosphere, which is made of solar plasma and solar magnetic fields. This gigantic structure is about three times wider than the orbit of Pluto, researchers said.
Specifically, the Voyagers are plying the heliosphere’s outer shell, a turbulent region called the heliosheath.
“We’re smelling, we’re touching the ionized matter in the heliosheath,” said Merav Opher of Boston University, a Voyager guest investigator.
The Voyagers are helping scientists better understand the mysterious heliosphere. For example, measurements from the spacecraft revealed that the structure is distorted and asymmetric, yanked out of shape by the interstellar magnetic field, researchers said.
And in June 2010, Voyager 1 measured the outward velocity of the solar wind — the million-mile-per-hour stream of charged particles coming from the sun — to be zero in its location in the heliosheath. That surprising reading hasn’t changed since.
Researchers don’t think the solar wind has stopped out there; they believe it may have just turned a corner. So they’ve recently started ordering Voyager 1 to do a series of acrobatic maneuvers, to point its instruments in different directions so the craft can pick up and track the puzzling solar breeze.
The heliosheath looks to be about 3 to 4 billion miles (4.8 to 6.4 billion km) thick, and the spacecraft are already well into it. Based on their speed, they should be out in about five years, Stone said.
That time frame is manageable. The Voyagers’ radioisotope thermoelectric generators — which convert the heat emitted by plutonium’s radioactive decay into electricity — can power their instruments until at least 2020. And the spacecraft have enough hydrazine fuel left to perform maneuvers for another 60 years, researchers said.
Of course, there are no signposts marking the start of interstellar space, where the Voyagers will escape the sun’s wind and magnetic field only to be buffeted by those of other, far-flung stars. So astronomers will probably have a hard time knowing when the historic moment occurs.
“We are starting to talk about what we expect to see,” Stone said. “I suspect, like in the past, we will be surprised, and we may in fact have a debate for a year or two before we finally decide, ‘We have crossed the boundary.'”
Courtesy-Space.com by Mike Wall, SPACE.com Senior Writer