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Jul-05-2008The laboratory at the end of the solar system(topic overview)
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Today, in Nature, an analysis of recent data streamed back from the Voyager 2 spacecraft helps build up a picture of how the Sun interacts with the rest of the galaxy. The current mission of both spacecraft is to reach and study the outer limits of the heliosphere - a magnetic 'bubble' around the Solar System created when the particles that stream out from the Sun crash into and hold back the soup of particles in the rest of interstellar space. When the solar wind senses the edge of the bubble, called the heliopause, located at 7-8.5 billion miles from the Sun, it prepares for the impending collision at the "termination shock", where the solar wind slows down to subsonic speed Prof Edward Stone of Caltech and colleagues report that Voyager 2 crossed this boundary closer to the Sun than expected, suggesting that the heliosphere in the south is dented, or pushed in, closer to the Sun by the interstellar magnetic field. Voyager 1 passed the termination shock at about 8.7 billion miles from the Sun, while Voyager 2 reached its more southerly edge, sooner than expected, passing the shock at about 7.8 billion miles. This reveals that the heliosphere is squashed inward in the south compared to the north. [1] Because Voyager 2 crossed the heliosheath boundary, called the solar wind termination shock, about 10 billion miles away from Voyager 1 and almost a billion miles closer to the sun, it confirmed that our solar system is " squashed" or " dented"- that the bubble carved into interstellar space by the solar wind is not perfectly round. Where Voyager 2 made its crossing, the bubble is pushed in closer to the sun by the local interstellar magnetic field. "Voyager 2 continues its journey of discovery, crossing the termination shock multiple times as it entered the outermost layer of the giant heliospheric bubble surrounding the Sun and joined Voyager 1 in the last leg of the race to interstellar space." said Voyager Project Scientist Dr. Edward Stone of the California Institute of Technology, Pasadena, Calif.[2]
Data from Voyager 2, described in a series of papers today in Nature, show that the craft entered the termination shock on August 31, 2007, at a distance from the sun of about eight billion miles (13 billion kilometers) and crossed it the next day. That's 10 percent closer to the sun than when the craft's sister ship, Voyager 1, passed through the same shock wave in late 2004 heading outbound from the solar system in a different direction. That far from the sun, the density of solar wind is, at most, a couple of protons and electrons per gallon, astrophysicist J.R. Jokipii of the University of Arizona Lunar and Planetary Laboratory in Tucson says. "It's almost impossible to measure. You have to give it to these experimenters," he says. Voyager 2 will now follow its twin into the heliosheath, the region of slower-moving wind beyond the termination shock. Besides confirming earlier research that hinted at the lopsided heliosphere, the crossing provides new details, including the energy and speed of the solar wind, that Voyager 1 could not pick up because its plasma detection instrument had stopped functioning.[3]
The signals reveal that at a distance of 83.7 astronomical units (1 AU is the average Earth-sun separation), Voyager 2 had at least five encounters with a turbulent region known as the termination shock, the researchers report in the July 3 Nature. That'''s the place where the solar wind ''' the sun'''s hot supersonic wind of protons and other charged particles, which carves the heliosphere, a bubble in space extending well beyond the orbit of Pluto ''' slams into cold interstellar space and abruptly slows. Analyzing the encounter is critical for understanding how the bubble interacts with surrounding space, and how the bubbles carved by other stars affect their surroundings, notes Voyager lead investigator Ed Stone of the California Institute of Technology in Pasadena, Calif. Researchers had expected that Voyager 2 would have only one encounter with the shock. The multiple crossings indicate that '''the shock is not the steady structure that is predicted by the simplest theory,''' says Len Burlaga of NASA'''s Goddard Space Flight Center in Greenbelt, Md. '''It is like a wave approaching a beach, that grows, breaks, dissipates, and then re-forms closer to shore.''' ON THE EDGE Location of the two Voyager spacecraft at the fringes of the solar system and the STEREO spacecraft.[4] KITCHEN SINK HELIOSPHERE: If the solar wind is like a stream of water spreading out on a flat sink bottom, then the boundary where the flow breaks against onrushing soapy water (interstellar gas) is the termination shock (recently encountered by the spacecraft Voyager 2) and the region of slower-moving water beyond it is the heliosheath. Hurtling through space 31 years after its launch, the Voyager 2 spacecraft has sent back the most detailed view yet of the shock wave that marks the thinning of the solar wind, the charged particles streaming from the sun.[3] Voyager 2 has revealed some amazing information, as it has found that the solar system is actually shaped like an egg. The Voyager 2 continues its journey toward interstellar space, and has found send data back which has revealed to scientists that the solar system is actually shaped like an egg. Both the Voyager 1 and the Voyager 2 have crossed the egd of the solar system, known as the termination shock. At this location, the outbound solar wind hits with the inbound energetic particles from interstellar space.[5] The solar wind blows in all directions, carving a bubble into interstellar space that extends past the orbit of Pluto. This bubble is called the heliosphere, and Voyager 1 was the first spacecraft to explore its outer layer, when it crossed into the heliosheath in December 2004. As Voyager 1 made this historic passage, it encountered the shock wave that surrounds our solar system called the solar wind termination shock, where the solar wind is abruptly slowed by pressure from the gas and magnetic field in interstellar space.[2] The beginning of the transition zone between the heliosphere (the solar wind bubble) and the rest of interstellar space is known as the 'termination shock'. Scientists report that Voyager 2 crossed this boundary closer to the sun than expected, suggesting that the heliosphere in this region is pushed inward, closer to the sun, by an interstellar magnetic field. These findings help build up a picture of how the sun interacts with the surrounding interstellar medium.[6] Originally launched in 1977, Voyager 2 last August reached the edge of the Sun's influence -- known as the heliosphere -- and encountered the region known as the termination shock where the solar wind slams into cold interstellar space.[7] Voyager 2 recently passed what is known as termination shock, when outbound solar wind hits with the inbound energetic particles from interstellar space. It surrounds the entire solar system, holding it in something called a heliosphere.[8] A collection of five papers in tomorrow's issue of the journal Nature analyze the data sent back from Voyager 2 as it reached a turbulent frontier known as the termination shock. The sun is constantly spewing out particles in all directions; as these particles move through the solar system, they are known as the solar wind. This wind pushes back against the interstellar plasma that exists throughout the galaxy.[9] Voyager 2's crossing of the termination shock represented a huge advance in our understanding of the geography of the solar system. Since no data was returned from Voyager 1, this represents the only realistic possibility for humanity to gather in situ data from this region of space for many years. While both probes may be beyond the influence of most of the solar wind, their time remaining in the heliopause will give them the chance to send back even more information that we already have.[10] The results, reported in the July 3 issue of the journal Nature, clear up a discrepancy in the amount of energy dumped into space by the decelerating solar wind that was discovered last year when Voyager 2 crossed the solar system's termination shock and entered the surrounding heliosheath.[11] Two University of Iowa space physicists report that the Voyager 2 spacecraft, which has been traveling outward from the Sun for 31 years, has made the first direct observations of the solar wind termination shock, according to a paper published in the July 3 issue of the journal Nature.[12]
Launched in 1977 on a historic trek of the outer planets, Voyager 2 has now crossed the turbulent boundary, known as the "termination shock," where the heliosphere yields to interstellar space. Its twin probe Voyager 1, crossed the same threshold four years earlier at a different spot some 1.5 billion kilometres (one billion miles) farther from the Sun. This difference proves that the heliosphere is not even close to perfectly round, but is oblong, like an egg, according to the studies, released by the British journal Nature on Wednesday.[13] This boundary is called the termination shock front and the space that it defines is called the heliosphere. Voyager 1 already crossed this boundary in 2004, but some of its sensors had failed before the probe got to the termination shock, so scientist weren't able to get enough information about the physical phenomena that take place in that region. Because of this, Voyager 2 remained the scientists' only hope to gather that kind of information for many years to come.[14]
The probe encountered the termination shock 10 AU closer to the sun than Voyager 1 did (one astronomical unit is the average distance between the Earth and the Sun). Voyager 2 crossed at 83.7 AU, while Voyager 1 crossed at 94.1 AU. When correcting for changes in solar wind pressure due to solar cycles, astronomers conclude that the termination shock has a seven to eight AU asymmetry in its shape.[10] Given the difference in times and locations, it was expected that the two probes would encounter the termination shock at different radial locations. Before Voyager 2 crossed the termination shock, scientists observed interstellar hydrogen and helium flow directions; from these it was thought that the interstellar magnetic field is tilted about 60 o relative to the flow direction. This should result in the southern portion of the termination shock being closer to the sun when compared to the northern portion of the shock. Voyager 2's crossing at about 45 o to the south in heliolongitude terms confirmed this idea.[10] First of all, Voyager 2 crossed the termination shock about 1 billion miles closer to the sun, confirming the theory of some scientists that the heliosphere is egg-shaped, and not round as others considered it should be. One explanation for this is given by the differences in the magnetic field of our galaxy, which are supposedly caused by star explosions.[14] Voyager 1 had already crossed the boundary in December 2004. It is about 10 billion miles away from Voyager 1 and almost a billion miles farther from the sun. Scientists think this indicates that the bubble is pushed in closer to the sun by the local interstellar magnetic field where Voyager 2 made its crossing. This makes it more of a squashed rectangular shape rather than a circle.[15] Voyager 1 had crossed the boundary in December 2004 about 10 billion miles away from Voyager 1 and almost a billion miles farther from the sun. Scientists think this indicates that the bubble carved into interstellar space by the heliosphere, which extends well past the distant orbit of Pluto, is not perfectly round, and the solar system is shaped a bit like an oblong.[16]
Launched in 1977, the Voyager 1 and Voyager 2 unmanned probes are now studying the edges of the heliosphere, the huge magnetic "bubble" around our solar system created by the solar wind as it runs up against the thin gas in interstellar space.[16] Voyager 2's journey toward interstellar space has revealed surprising insights into the energy and magnetic forces at the solar system's outer edge, and confirmed the solar system's squashed shape. Both Voyager 1 and Voyager 2 continue to send data to Earth more than 30 years after they first launched.[17] Nobody expected to take it this far. When NASA launched two probes named Voyager 1 and Voyager 2 in the summer of 1977, scientists hoped the probes would get as far as Saturn during their five-year mission. The nuclear-powered explorers are still sending data home over 30 years after their launch, and are currently pushing through the boundary of our solar system into interstellar space.[9]
PARIS (AFP) — Millions of textbooks depicting our Solar System as spherical have got it all wrong, according to studies of data sent back from deep space by NASA's venerable probe, Voyager 2. The Sun's zone of influence -- called the heliosphere -- turns out to be seriously asymmetrical, not round, they say.[13] New data sent back from NASA's Voyager 2 probe show that our solar system is not round, but dented, meaning millions of textbooks now have to be re-written.[18]
This artist's rendering depicts NASAs Voyager 2 spacecraft as it studies the outer limits of the heliosphere - a magnetic 'bubble' around the solar system that is created by the solar wind. Scientists observed the magnetic bubble is not spherical, but pressed inward in the southern hemisphere, according to recent data published as part of a series of papers in this week's (July 3, 2008) Nature.[6] ScienceDaily (July 3, 2008) - Scientists using data from NASA's Voyager 2 spacecraft have observed the bubble of solar wind surrounding the solar system is not round, but has a squashed shape, according to recent data published as part of a series of papers in this week's (July 3) Nature.[6]
The termination shock surrounds the solar system and encloses a bubble called the heliosphere. "The solar wind is blowing outward trying to inflate this bubble, and the pressure from interstellar wind is coming in," said Edward Stone, physicist and Voyager project scientist at Caltech in Pasadena, Calif. He and other researchers published a series of studies in the journal Nature this week that detail the Voyager findings.[17] Researchers have begun looking into whether the solar wind somehow sheds energy ahead of time. "Somehow the solar wind knows the shock is coming before it gets there, and theory says that shouldn't be," Richardson noted, adding that the solar wind speed drops from its supersonic speed of about 248 miles per second (400 km/s) to 186 miles per second (300 km/s) even before hitting the edge of the solar system. That speed falls more noticeably to about 93 miles per second (150 km/s) after the termination shock. Even as researchers continue parsing the Voyager findings, both spacecraft plow onward toward deep space and beyond all expectations of their original mission.[17] John Richardson of the Massachusetts Institute of Technology and his colleagues found that the temperature of protons ''' a main constituent of the solar wind ''' in the slowed-down region is five to 10 times cooler than expected. Using the STEREO spacecraft, Robert Lin and Linghua Wang of the University of California, Berkeley, and their colleagues trace the missing energy to a large group of '''pickup protons''''''particles that started out as neutral hydrogen atoms from interstellar space and then infiltrated the solar system. The solar wind ionized these atoms, turning them into protons that were then carried back out again by the wind, to the termination shock.[4] Each spacecraft has now crossed the edge of the solar system, known as the termination shock, where the outbound solar wind collides with inbound energetic particles from interstellar space.[17] Just a hair over 30 years later, it reached what is known as the termination shock. The sun is constantly spewing out particles in all directions; as these particles move through the solar system, they are known as the solar wind. This wind pushes back against the interstellar plasma that exists throughout the galaxy.[10] Various instruments searched for the force that is holding the shock front back, and it was found that energized "pickup ions" play a major role in the dynamics of the termination shock. These pickup ions are interstellar neutral atoms that are caught up in the solar wind and have become accelerated and ionized. One paper concluded that these ions account for more of the nonthermal partial pressure holding back the interstellar plasma than either the thermal plasma pressure or the pressure due to the magnetic field. Other papers asked how similar this shock front is to other shock fronts in the solar system.[10]
Gusts in the solar wind may cause the shock to '''come and go, re-forming itself and decaying,''' Stone suggests. Launched in 1977, Voyager 2 follows in the footsteps of its sister craft, Voyager 1, which headed toward the fringes of the solar system in the opposite direction, the northern celestial hemisphere, and passed through a single termination shock in 2004.[4] Voyager 2 generated data that revealed the spectrum produced by the electric field of the plasma in the area near the termination shock. It was found to be qualitatively similar to the observed bow shocks upstream of Jupiter, Saturn, Uranus, and Neptune. One difference between this set of observations and the data gather by Voyager 1 was that Voyager 1 saw anomalous cosmic rays as it neared the shock, and these did not peak when it crossed the shock. Voyager 2, on the other hand, saw no evidence of these anomalous cosmic rays, so their origin remains a mystery for now. Researchers feel that once both craft are clearly through to the heliosheath--the region beyond the termination shock--during the solar minimum, both can begin to measure the relative intensity gradient between the anomalous cosmic rays and more standard galactic cosmic rays.[10]
Up until now, the common perception was that it should stay at all times in the same position in space, but Voyager 2 passed through it several times. Another phenomenon that puzzled researchers was solar wind slowing down for apparently no reason before reaching the zone where it collides with interstellar particles. Both Voyager 1 and Voyager 2 are expected to enter the interstellar region in about 10 years. At this moment they are both travelling through the heliosheath, the region of space where solar wind and interstellar particles both manifest their influences.[14] San Francisco, CA. - NASA's Voyager 2 spacecraft has followed its twin Voyager 1 into the solar system's final frontier, a vast region at the edge of our solar system where the solar wind runs up against the thin gas between the stars. Voyager 2 took a different path, entering this region, called the heliosheath, on August 30, 2007.[2] BERKELEY ' NASA's sun-focused STEREO spacecraft unexpectedly detected particles from the edge of the solar system last year, allowing University of California, Berkeley, scientists to map for the first time the energized particles in the region where the hot solar wind slams into the cold interstellar medium.[11]
In 10 to 20 years after reaching the termination shock, NASA expects the craft to cross the heliopause, the outer edge of the heliosheath. That would mean they have exited the solar system and entered the interstellar medium. NASA engineers estimate that both probes' plutonium power packs have the potential to keep them broadcasting data until 2025. If we're lucky, Jokippi says, they'll let us know what they find.[3] '''Over the past few years, the stream of in situ and remote data from the outer reaches of the heliosphere has revolutionized our view of how the sun interacts with the galaxy,''' comments J.R. Jokipii of the University of Arizona in Tucson. More is to come, he adds, as the two Voyager craft continue their journeys past the termination shock, to the very edge of the solar system during the coming decade.[4]
Voyager 2 reached the southern edge of the solar system 7 billion miles (76 AU, or astronomical units) from the sun, closer than Voyager 1, which had reached the northern edge 7.8 billion miles (84 AU) from the sun. That confirms earlier suspicions about the heliosphere bubble being squashed at its southern region.[17] Voyager 2 reached the egde of the solar system 7 billion miles from the sun. This is nearly 1 billion miles closer than Voyager 1, meaning that the heliosphere is squished at one end.[5] Voyager 2 hit the southern edge of the solar system nearly 1 billion miles closer to the sun than Voyager 1 did to the north.[19]
The solar wind is made up of electrically charged particles blown into space in all directions by the sun. In August 2007 Voyager 2 crossed this boundary 7.8 billion miles from the sun.[15]
According to the new data, the wind downstream of the shock was cooler and faster moving than researchers had anticipated. The interpretation, says Jokippi, who wrote an editorial accompanying the Nature reports, is that the solar wind is imparting energy to neutral atoms from the interstellar gas and causing them to ionize. These "pickup" ions are then accelerated to speeds of hundreds of miles (kilometers) per second, exerting a strong effect on the structure of the shock, he says. The twin Voyager craft set out for deep space in 1977 to study Jupiter and Saturn, but after their primary mission was completed, they kept on going.[3] Voyager 1's plasma detector failed after it passed Saturn, so Voyager 2 provided the first glimpse of what happens to the solar wind's energy as it slams into interstellar space.[17] The Voyager 2 spacecraft has a working Plasma Science instrument that can directly measure the velocity, density and temperature of the solar wind. This instrument is no longer working on Voyager 1 and estimates of the solar wind speed had to be made indirectly.[2]
An artist's rendering of Voyager 2 in the outer limits of the heliosphere, the area of space affected by the Sun's solar wind.[17] The heliosphere is a volume over which the effects of the solar wind extend, stretching from the sun to more than twice the distance of Pluto. Beyond its edge, called the heliopause, lies the relative quiet of interstellar space, at about 100 astronomical units (AU) - 100 times the Earth-sun distance.[11] Researchers say the crossing confirms that the heliosphere--the region swept out by the solar wind --is actually lopsided, perhaps due to a tilted magnetic field in local interstellar space.[3] The magnetic field hits the solar system at a different angle on the south than on the north, probably because of interstellar turbulence from star explosions, said Voyager project scientist Ed Stone. Both spacecraft still have several more years before they completely exit the solar system and continue deeper into the space between stars, said Stone, former director of NASA's Jet Propulsion Lab.[19] Voyager 2 hit the edge at 7.8 billion miles from the sun. "We used to assume that it's all symmetric and simple," said Leonard Burlaga, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It's literally like a hand pushing." That push is from the magnetic field that lies between star systems in the Milky Way.[19]
The location of the shock detected by Voyager 2 ''' some 1.6 billion kilometers closer to the sun than the Voyager 1 shock ''' suggests that the solar system is lopsided.[4] Four years earlier, Voyager 1 crossed the "terminal shock" boundary in a different spot in the solar system. Combining the data gathered by both 31-year-old probes show our solar system is oblong, like an egg, with a flattened bottom.[18] The two nuclear powered probes continued to speed onwards to the outer Solar System, each flying in slightly different directions, with Voyager 1 becoming the most distant man-made object in space in the 1990s.[1] For decades to come, the two spacecraft -- speeding outward at more than 17 kilometers per second (38,000 miles per hour) -- will be the only source of local observations of the far limits of our Solar System. The probes were originally sent to fly by and observe Jupiter and Saturn, which they did with thrilling results, including the discovery of active volcanoes on Jupiter's moon Io, and unknown intricacies in Saturn's rings. After that their mission was reconfigured to explore space beyond the Solar System's planets. They became the first man-made objects to enter these cold, dark reaches, powered by long-life nuclear batteries in the absence of solar energy. The spacecraft are so distant that commands from Earth, travelling at light speed, take more than a dozen hours to reach them.[13] Information from Earth's first space probes to hit the thick edge of the solar system — called the heliosheath where the solar wind slows abruptly — paint a picture that is not the simple circle that astronomers long thought, according to several studies published Thursday in the journal Nature. Surprised astronomers said they will have to change their models for what the solar system looks like.[19]
At the end of the solar system, the solar wind finally begins to lose out and its speed drops below the speed of sound (relative to the interstellar medium), resulting in a roughly spherical shell known as the termination shock front.[9] The termination shock is the region of the heliosphere where the supersonic solar wind slows to subsonic speed as it merges with the interstellar medium.[11]
At the termination shock the solar wind, which continuously expands outward from the sun at over a million miles per hour, is abruptly slowed to a subsonic speed by the interstellar gas.[12]
According to Lin, the neutral atoms are probably hydrogen, since most of the particles in the local interstellar medium are hydrogen. The charge exchange between hot ions and neutral atoms to generate energetic neutral atoms is well known around the sun and planets, including Earth and Jupiter, and has been used by spacecraft such as IMAGE and Cassini as a means of remotely measuring the energy in ion plasmas, since neutral atoms travel much farther than ions. A new NASA mission, the Interstellar Boundary Explorer (IBEX), is planned for launch later this year to map more thoroughly the lower-energy energetic ions in the heliosheath by means of energetic neutral atoms to discover the structure of the termination shock and how hydrogen ions are accelerated there.[11] Wang'''s team found that the sensors had detected a group of particles from the termination shock region that didn'''t fluctuate in intensity and therefore must be neutral. These particles started out as pick-up protons. The Berkeley-led team concluded that these particles came from the interstellar medium, providing the first map of particles from just beyond the solar system. This new map is especially important because material at the solar system'''s edge is too tenuous and faint to be imaged by a visible-light telescope.[4]
"The important new data describing the termination shock are still being pondered, but it is clear that Voyager has once again surprised us," said Dr. Eric Christian, Voyager Program Scientist at NASA Headquarters, Washington. The two Voyager spacecraft will be the only source of local observations of this distant but highly interesting region for years to come.[2] Almost 30 years to the day after it launched, between August 31st and September 1st of last year, Voyager 2 crossed the termination shock, and captured a great deal of information in the process. This week's edition of Nature contains a series of five papers, plus a News and Views article, on the data sent back by Voyager 2 as it crossed the termination shock.[10] Voyager 2 was launched Aug. 20, 1977. It visited four planets and their moons in the course of its journey into space. Its sister spacecraft Voyager 1, which was launched Sept. 5, 1977, crossed the termination shock in December 2004 - earlier than Voyager 2 because of a faster trajectory.[1] Comparing the Voyager 1 crossing in December 2004 with the Voyager 2 crossing in August 2007 allowed scientists to confirm that the second sibling actually crossed the termination shock and passed into the heliosheath, an outer layer of the heliosphere.[17]
Since Voyager 1 has some issues after it went by Saturn, Voyager 2 is providing the first view into what happens at the termination shock. Share and Enjoy: These icons link to social bookmarking sites where readers can share and discover new web pages.[5] The heliosphere is shaped more like an egg than anything else. This is the first time researchers have been able to see what happens at the termination shock point. Share and Enjoy: These icons link to social bookmarking sites where readers can share and discover new web pages.[8] NASA says the probe encountered the termination shock over August 31 and September 1 of last year, and surprised researchers by crossing the boundary several times. The multiple crossings indicate that '''the shock is not the steady structure that is predicted by the simplest theory,''' says Len Burlaga of NASA'''s Goddard Space Flight Center in Greenbelt, Md. '''It is like a wave approaching a beach, that grows, breaks, dissipates, and then re-forms closer to shore".[9] The Voyager II space probe has been the little engine that could, faithfully beaming back information on a weekly basis for the last 30 years, and it is approaching what is known as termination shock.[20]
Houston, TX-When it was launched August 20th, 1977 the Voyager II probe was expected to report back for several years about the different planets and space features it encountered.[20]
Voyager 1 passed through the shock in a different region several years ago but vexed scientists by failing to send back data during that crucial transition. That made Voyager 2's observations all the more critical.[9] Message from a craft at the solar system's final frontier holds surprises. The craft recently sent back surprising data as it approached this edge. There are no signs to announce the edge of the solar system, but when the venerable Voyager 2 spacecraft approached this final frontier last Aug. 31 it was in for quite a shock.[4] The Voyager 2 has been sending back data for 30-years as it heads towards interstellar space, and has revealed that our solar system is shaped like a big egg.[8] Seasoned space traveller Voyager 2 has surprised scientists as it approaches the edge of the solar system with data that shows the solar system to be oblong shaped, not spherical as previously thought.[7] WASHINGTON (Reuters) - The solar system may not be a nice round shape, but rather a bit squashed and oblong, according to data from the Voyager 2 spacecraft exploring the solar system's outer limits, scientists said on Wednesday.[16]
Boston (ChattahBox) - According to new data sent back from Voyager 2, our solar system appears to be nothing but a giant egg.[8] New data form the Voyager 2 craft and STEREO are providing fresh insight about the structure of the edge of the solar system.[4]
The Solar System is not round, but an egg shape with its bottom edge squashed inward, according to data beamed back from a three decade old space probe.[1] In 1977, NASA launched two space probes on missions beyond the solar system.[19] WASHINGTON (AP) — When viewed from the rest of the galaxy, the edge of our solar system appears slightly dented as if a giant hand is pushing one edge of it inward, far-traveling NASA probes reveal.[19]
Prior to the actual event, researchers had expected a fairly simple crossing, with the probe moving from a region where the solar wind was supersonic to one where it was subsonic. What they found instead was a "complex, rippled, quasi-perpendicular supercritical magnetohydrodynamic shock of moderate strength undergoing reformation on a scale of a few hours."[10] At the termination shock, the solar wind slows and dumps a large amount of energy into space. This energy must then exist in some form, such as heat.[4] Richardson et al. Cool heliosheath plasma and deceleration of the upstream solar wind at the termination shock.[6] Gurnett et al. Intense plasma waves at and near the solar wind termination shock.[6]
An added mystery remains as to why the solar wind slows down early, as though anticipating running headlong into the termination shock.[17] Decker et al. Mediation of the solar wind termination shock by non-thermal ions.[6]
The shock wave, or heliospheric termination shock, occurs when the supersonic wind thins to the point that it can no longer rebuff the denser haze of charged particles flowing through interstellar space.[3] Voyager 2 has now crossed the so-called "terminal shock" boundary. It is here that the heliosphere from the sun succumbs to interstellar space.[18] Voyager 2 also crossed the "termination shock" several times within the space of a single day, showing that the boundary is in perpetual flux, like the ebb-and-flow of a tide. University of Arizona astronomer Randy Jokipii paid tribute to the two Voyagers, which have been operating faithfully since their launch in 1977.[13]
Instead of moving through the shock front once, Voyager 2 underwent five distinct crossings over a two day period. This was due to the dynamic nature of termination shock fluctuations; in fact, the time between crossings is on the order of magnitude expected for ripples propagating through the shock.[10] The newly discovered population of ions in the heliosheath contains about 70 percent of the energy dissipated in the termination shock, exactly the amount unaccounted for by Voyager 2's instruments, the UC Berkeley physicists concluded.[11] Gurnett said, "There is no way for us to make direct measure of a super nova shock, so the Voyager 2 measurements at the termination shock provide us the best opportunity in the foreseeable future to understand how cosmic rays are produced by supernova cosmic shocks."[12] Voyager 2 also carries more working instruments that show the termination shock in full detail.[17]
Kurth noted that while some aspects of the termination shock matched scientists' expectations, a number of the observations made by Voyager were surprising and will cause a number of theories to be revised.[12]
Don Gurnett, professor of physics in the College of Liberal Arts and Sciences and principal investigator for the plasma wave instrument on Voyager 2, and Bill Kurth, UI research scientist and Voyager co-investigator, said that the shock crossing was marked by an intense burst of plasma wave turbulence detected by the UI instrument, as well as by various effects detected by other instruments on the spacecraft.[12] At the time of the shock crossing, August 31, 2007, Voyager 2 was at a distance of 83.7 astronomical units (AU), roughly twice the distance between the Sun and Pluto. At this great distance, it took 11.2 hours for the radio signal from the spacecraft to reach Earth.[12] Results on the Voyager 2 shock crossing from the entire Voyager science team are being presented at the Fall 2007 meeting of the American Geophysical Union in San Francisco. The Voyagers were built by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., which continues to operate both spacecraft.[2]
Voyager 1 may have had only a single shock crossing and it happened during a data gap. Voyager 2 had at least five shock crossings over a couple of days (the shock " sloshes" back and forth like surf on a beach, allowing multiple crossings) and three of them are clearly in the data. They show us an unusual shock.[2]
The current mission of Voyager 2, and its sister Voyager 1, is to reach the edge of interstellar space.[6] "The Holy Grail for me will be when the spacecraft begin traveling in pure interstellar space," Jokipii said. "That's maybe 10 years away. Scientists now can start thinking about what they want to look for when the Voyagers break through the last barriers to true interstellar space."[7] The "bottom" of the egg is flattened by a permanent clash of particles, as the outbound solar wind smashes into atomic debris hurtling in from interstellar space, the scientists theorise.[13] The heliosphere comprises space dominated by the solar winds, or particles blasted out by the Sun. It goes way beyond the orbit of Pluto, which circles the Sun at a distance of nearly six billion kilometers (four billion miles).[13] The solar wind is a thin gas of electrically charged particles (plasma) blown into space by the sun.[2] About 80 percent of the energy released when the solar wind slows goes into accelerating the pickup protons, the researchers report. The STEREO findings were a surprise because detectors on the twin craft are designed to detect energetic charged particles coming from the sun, which fluctuate in intensity due to variations in the solar magnetic field that pushes them around.[4] Solar wind is swept along by the sun's magnetic field, which means it cascades like a fluid instead of crashing like billiard balls.[3]
The heliosphere, or the zone in which our sun has influence through solar winds, is asymmetrical, according to the Voyager data.[18] In their early years they produced some of the first close up images of the large outer. It is entering a vast, turbulent expanse, where the sun's influence ends and the solar wind crashes into the thin gas.[6] The solar wind travels outwards from the sun at supersonic speeds and at temperatures near 17,540 degrees Fahrenheit (10,000 degrees Kelvin).[17]
Dr John Richardson of the Massachusetts Institute of Technology, Cambridge, who discusses what happens to the energy of the solar wind in another Nature paper, added that the little probes will begin true interstellar travel in another decade.[1] The solar wind's missing energy ended up hitching a ride with interstellar intruders, Richardson said.[17]
Neutral atoms that flowed in from outside the solar system became energized upon entering the heliosheath layer, and then ended up stealing 80 percent of the energy from the solar wind. Researchers have yet to puzzle out the significance of this.[17]
The Voyager spacecraft were launched with a mission to fly by and observe the giant planets Jupiter and Saturn. The two spacecraft then continued their mission into the outer solar system. They are flying through remote, cold and dark conditions, powered by long-life nuclear batteries in the absence of solar energy.[15] The outer limits of the system of planets around our own Sun, where the influence of our local star ends, are being probed by the Voyager spacecraft, which were launched in 1977 on a five year mission to study Jupiter and Saturn.[1]
Gurnett noted that Voyager 2, launched in 1977, is moving at a speed of 38,000 miles an hour. Even at this considerable speed, the spacecraft will still take 30,000 years to reach a distance equal to that of the nearest star.[12]
Voyager 2 found a much lower temperature beyond the shock than was predicted. This probably indicates that the energy is being transferred to cosmic ray particles that were accelerated to high speeds at the shock.[2] A report in the British journal Nature has said because Voyager 2 had a number of encounters with the shock, the original theory of the heliosphere being round is incorrect, with the discovery that it is much more oblong.[7]
The termination shock is around the entire solar system, holding it in something called a heliosphere.[5] The reason for that asymmetrical shape rests with an interstellar magnetic field that puts more pressure on the southern region of the solar system something that may change over 100,000 years as that magnetic field experiences turbulence, Stone said.[17] The dent may be due to extra pressure exerted by the Milky Way galaxy'''s magnetic field. The field is generally uniform but could have become '''tilted in such a way that it'''s pushing more on the south than the north,''' says Stone. A series of supernova explosions in the solar neighborhood about 10 million to 20 million years ago could have tilted the field, he notes.[4]
The twin STEREO spacecraft were launched in 2006 into Earth's orbit about the sun to obtain stereo pictures of the sun's surface and to measure magnetic fields and ion fluxes associated with solar explosions.[11] ENAs are formed when energetic electrically-charged particles " steal" an electron from another particle. Once neutral, they travel straight, unaffected by the solar magnetic field.[2] "The suprathermal electron sensors were designed to detect charged electrons, which fluctuate in intensity depending on the magnetic field" said lead author Linghua Wang, a graduate student in UC Berkeley's Department of Physics. "This is the first mapping of energetic neutral particles from beyond the heliosphere" Lin said. "These neutral atoms tell us about the hot ions in the heliosheath.[11]
Between June and October 2007, however, the suprathermal electron sensor in the IMPACT (In-situ Measurements of Particles and CME Transients) suite of instruments on board each STEREO spacecraft detected neutral atoms originating from the same spot in the sky: the shock front and the heliosheath beyond, where the sun plunges through the interstellar medium.[11] The heliosheath is the region of roiled plasma between the shock front and the interstellar medium.[11]
"We're actually seeing the shock for the first time," said John Richardson, principal scientist for Voyager's Plasma Physics instrument at MIT in Cambridge, Mass.[17] "We hope the Voyagers will cross the heliopause boundary in about 10 years and be the first spacecraft to measure what is outside of the Sun's heliosphere."[1] The Voyager spacecraft are the most distant human-made objects in space -- with Voyager 1 more distant than Voyager 2.[6] Voyager 1 went north and Voyager 2 went south. What startled astronomers is that when the two of them hit the heliosheath they did so at different distances from the sun.[19] Its twin, Voyager 1, crossed the same threshold some four years earlier at a different juncture.[7]
Voyager 1's flight path at Saturn bent it up and away from the ecliptic, the plane in which most planets orbit the sun.[6]
"The stream of in situ and remote data from the outer reaches of the heliosphere has revolutionized our view of how the Sun interacts with the Galaxy." Looking to the future he said the real test will come when the craft begin exploring interstellar space. [7] IBEX will detect some of the particles that happen to be headed towards the Earth, and the number and energy of the particles coming from all different directions will tell us much more about the overall structure of the interaction between the heliosphere and interstellar space.[2] The Interstellar Boundary Explorer (IBEX), led by Dr. David McComas of the Southwest Research Institute in San Antonio, Texas, will use energetic neutral atoms (ENAs) to create all-sky maps at various energies of the interaction of the heliosphere with interstellar space.[2]
Scientists had predicted that the solar wind would simultaneously slow down and heat up to a temperature near 1.8 million degrees F (1 million degrees Kelvin), but instead found that it reached just 180,000 degrees F (100,000 degrees Kelvin) at the solar-system boundary. [17] 'Imagine a balloon is being blown up by the solar wind,' Edward Stone from the California Institute of Technology told the journal Nature.[15]
Scientists with the Texas A&M's Fruit and Vegetable Improvement Center have found that an organic compound found in watermelon acts somewhat similar to sildenafil citrate, better known under its. The innermost planet of the solar system, Mercury, revealed its mysteries 33 years after the first flyby performed by Mariner 10 in 1974-1975. [14] Researchers studying the flow of energy at the solar system'''s edge found another surprise.[4]
Even though Voyager 2 is the second spacecraft to cross the shock, it is scientifically exciting for a couple of reasons. [2] Voyager 2's trajectory continued in the ecliptic, allowing the spacecraft two more planetary encounters, the distant planets Uranus and then Neptune.[6]
The sounds of Voyager's encounter with shock waves at various planets and other sounds of space can be heard by visiting the space audio Web site at: http://www-pw.physics.uiowa.edu/space-audio/. [12] JPL manages the Voyager mission for NASA's Office of Space Science, Washington, D.C. Share and Enjoy: These icons link to social bookmarking sites where readers can share and discover new web pages.[12]
In the summer of 2008, NASA will be launching a mission specifically designed to globally image the termination shock and heliosheath remotely from Earth orbit.[2] The termination shock is believed to be responsible for the origin of less energetic cosmic rays called "anomalous cosmic rays." The recent observations at the termination shock are expected to help physicists understand how cosmic rays are produced by the turbulent fields that exist in such shocks.[12] The discovery that shattered what scientists thought about the termination shock is that it seems to fluctuate.[14] Explaining the termination shock, University of Arizona Professor J. Randy Jokipii said in a UA statement last year: "Termination shocks are not unique to the heliosphere.You can see one in water running in your kitchen sink.[7]
Each Voyager logs approximately 1.6 million kilometres (one million miles) per day. Should they ever encounter extraterrestrial intelligence, the two probes each carry a time capsule, a "golden record" of sounds and images about life on Earth in the mid-1970s. [13]
SOURCES
1. Voyager pictures reveal Solar System is egg-shaped - Telegraph
2. Voyager Alters Our View of the Solar System - Space - redOrbit
3. Voyager 2 Finds Lopsided Solar System: Scientific American
4. Science News / Postcards From The Edge
5. Voyager 2 Reveals That The Solar System Is Shaped Like An Egg : dBTechno
6. Voyager Squashes View Of Solar System
7. Voyager 2 finds egg-shaped solar system - Science
8. According To Voyager 2, Our Solar System Is A Giant Egg : ChattahBox
9. Voyager 2 | 80beats | Discover Magazine
10. The laboratory at the end of the solar system
11. First images of solar system's invisible frontier
12. UI researchers make first measurements of the solar wind termination shock | SpaceRef - Your Space Reference
13. AFP: Solar System is egg-shaped, scientists find
14. Voyager 2 Sends Data from the Edge of the Solar System
15. Our solar system is egg-shaped, according to distant space probe | Mail Online
16. Solar system a bit squashed, not nicely round | Science | Reuters
17. FOXNews.com - Space Probes Find Dent in Solar System - Science News | Science & Technology | Technology News
18. Voyager Data Changes Shape of Solar System
19. The Associated Press: Space probes show solar system dented, not round
20. Voyager II Reports Back From Deep Space - EON
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