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  • richardmitnick 9:29 am on April 29, 2020 Permalink | Reply
    Tags: , , , , , Heliopause, , NASA Voyager 1 and 2 missions   

    From Astronomy Magazine- “Voyager: What’s next for NASA’s interstellar probes?” 

    From Astronomy Magazine

    April 28, 2020
    Eric Betz

    Thousands of years from now, Voyager 1 and Voyager 2 will leave our solar system. But their instruments will stop working long before that happens.

    NASA/Voyager 1

    NASA/Voyager 2

    In 1977, NASA launched the twin Voyager spacecraft to probe the outer reaches of our solar system. The space agency was still in its infancy then. But with the triumph of the Apollo Moon landings just five years behind them, NASA was ready to dive headfirst into another bold idea.
    Thanks to a rare alignment of the solar system’s four outer planets — which happens just once every 175 years — the agency had the chance to redefine astronomy by exploring Jupiter, Saturn, Uranus and Neptune in one fell swoop.

    The scheme was a stunning success.

    At Jupiter, the probes surprised scientists when they spotted volcanoes on the moon Io and discovered Europa is likely an ocean world. Saturn surrendered its atmospheric composition and new rings. And Voyager 2 returned humanity’s only close-up looks at Uranus and Neptune. To this day, scientists are still making new discoveries by exploring Voyager’s decades-old data.

    But these probes haven’t stopped scouting the outer solar system. Voyager 1 and Voyager 2 are still functioning today, making them the longest-running and most-distant space mission in history. Though they are each taking different paths, both spacecraft are still screaming their way out of the solar system. And they still have a long way to go.

    The two Voyager spacecraft took different paths through the solar system, and both have since left the sun’s influence entirely. Credit: NASA/JPL-Caltech

    Where are the Voyager Probes Going?

    Even traveling at 35,000 mph, the Voyager probes will need another 300 years just to reach the inner edge of the Oort Cloud — a large sphere of icy space rocks that begins a couple of thousand times farther from the Sun than Earth. The outer edge of the Oort Cloud may be so distant that it take the Voyager probes 30,000 years or more to completely cross it, according to NASA.

    After that, in about 40,000 years, Voyager 1 could finally approach another star. Voyager 2, however, will need 300,000 years before it comes close to bathing in the light of another star.

    Thankfully, we don’t have to wait that long for new discoveries. Both probes are still making fascinating finds along the way.

    Only the Voyager probes have passed the heliopause, leaving the sun’s influence. New probes may one day study the interstellar medium lying beyond. Credit: NASA-JPL/Caltech

    What is the Voyager Mission Studying?

    Back in 2012, Voyager 1 became the first spacecraft to reach interstellar space. There are no road signs letting NASA know that the craft broke the barrier. Instead, they determined it thanks to measurable changes Voyager 1 detected when it hit a region called the heliopause.

    Our Sun produces an intense stream of particles, dubbed the solar wind, that flows outward in all directions and creates a magnetic field that shields the planets from interstellar particles. The powerful wind carves a huge cavity in the interstellar medium (the region between stars) that encapsulates all the planets. This protective bubble is called the heliosphere, and the heliopause is its outer boundary — where our Sun’s influence is finally overpowered by distant activity like erupting supernovas.

    Scientists were surprised when Voyager 1 measured the magnetic field just inside and just outside of the heliopause, finding no significant changes in its overall direction. Then, when Voyager 2 reached this same boundary of interstellar space in 2018, it found similar results.

    But Voyager 2 offered up another surprise when NASA scientists released its first results from beyond the heliopause. They had originally expected that particles from our sun would not “leak out” of the heliosphere into interstellar space. And Voyager 1 saw no such leakage. But Voyager 2 found the opposite. It recorded a small trickle of solar particles streaming through the heliopause.

    In recent years, the twin probes also have discovered that the solar wind moves more slowly at our solar system’s edge than expected. All said, by studying data from the two probes, astronomers have been able to compare, contrast and confirm results about the boundary that separates our solar system from interstellar space.

    Alison Mackey/Discover

    When Will Voyager 1 and Voyager 2 Die?

    Since their launch more than 40 years ago, NASA has remained in near-constant contact with the Voyager probes. However, the space agency has temporarily stopped receiving messages from Voyager 2 while they work to repair and update one of the three Deep Space Network antennas used to communicate with the probes, The New York Times reported in March.

    It’s a risky move, and there’s a chance we may not hear from Voyager 2 once the receivers are turned back on. But Earth is still in contact with Voyager 1. And the discoveries haven’t ended quite yet. Mission planners intend to keep communicating with the spacecraft until they fail or lose power.

    Both should be able to keep at least one scientific instrument running until 2025. And even after that, NASA expects to continue receiving engineering data from the probes until 2035, when they exceed the range of the Deep Space Network antennas.

    Sadly, that means the so-called interstellar mission won’t be able to tell us what they see once they reach the stars.

    The Voyager golden record (left) is a 12-inch gold-plated copper disc. It’s covered with aluminum and electroplated with an ultra-pure sample of uranium-238. Credit NASA

    A Golden Record of the Journey

    Of course, NASA knew this day would come long before the missions launched. And this lonesome, one-way ticket out of the solar system was more than some astronomers could resist. Carl Sagan was so drawn to the idea that he helped NASA create an entire cultural component for the mission, lest some future aliens — or spacefaring earthlings — found one of the Voyager probes.

    Each spacecraft carries a golden record that serves as a time capsule from Earth, with their contents chosen by a committee led by Sagan. These messages to the stars contain sights and sounds from Earth, as well as music from dozens of countries and greetings spoken in 55 languages from around the world.

    So, while someday we’ll stop hearing back from the Voyager probes, it might not be the last message conveyed on their journey to the stars.

    “Billions of years from now, our Sun, then a distended red giant star, will have reduced Earth to a charred cinder,” Sagan opined. “But the Voyager record will still be largely intact, in some other remote region of the Milky Way galaxy, preserving a murmur of an ancient civilization that once flourished — perhaps before moving on to greater deeds and other worlds — on the distant planet Earth.”

    See the full article here .


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    Astronomy is a magazine about the science and hobby of astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy and those who want to know about sky events, observing techniques, astrophotography, and amateur astronomy in general.

    Astronomy was founded in 1973 by Stephen A. Walther, a graduate of the University of Wisconsin–Stevens Point and amateur astronomer. The first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained astrophotos and illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at the University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age. Although even in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would ever be able to earn a living. However he graduated in Journalism from the University of Wisconsin Stevens Point, and as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition. He died in 1977.

  • richardmitnick 9:35 am on August 20, 2019 Permalink | Reply
    Tags: "Sampling the Space Between the Stars", , ENAs-energetic neutral atoms, , Heliopause, Heliosheath, , ,   

    From Eos: “Sampling the Space Between the Stars” 

    From AGU
    Eos news bloc

    From Eos

    19 August 2019
    Mark Zastrow

    Data from the Cassini and Voyager spacecraft reveal new information about the Sun’s magnetic bubble.

    NASA/ESA/ASI Cassini-Huygens Spacecraft

    NASA/Voyager 1

    NASA/Voyager 2

    The basic shape and properties of the heliosphere, the protective magnetic bubble created by the solar wind, shown in this schematic are based on measurements of heliosheath proton distributions from Voyager 1 and 2 (illustrated in the diagram) and of energetic neutral atoms by Cassini. The location of the inner edge of the heliosheath, called the termination shock, is roughly 10 astronomical units (AU; 1 AU is equivalent to the mean Sun-Earth distance of about 150 million kilometers) farther from the Sun where Voyager 1 crossed it compared with Voyager 2, but the location of the outer edge, the heliopause, is about the same distance at along both Voyager trajectories. Red arrows represent the interstellar plasma flow deflected around the heliosphere bubble. Credit: K. Dialynas, S. M. Krimigis, D. G. Mitchell, R. B. Decker and E. C. Roelof

    Charged particles that spew into space as part of the solar wind create a protective magnetic bubble tens of billions of kilometers wide around the solar system. This bubble, called the heliosphere, plows through the harsh cosmic radiation of interstellar space.

    Understanding the physics at the bubble’s edge, called the heliosheath, is not easy. The boundary is in constant flux and pushes out against the broader interstellar magnetic field that permeates our corner of the Milky Way. Only two spacecraft—Voyager 1 and 2, originally launched by NASA in 1977—have ever traversed the frontiers of our local bubble.

    Now Dialynas et al. [Geophysical Research Letters] have combined Voyager data with observations from NASA’s Cassini mission, which orbited Saturn from 2004 to 2017, to gain more insight into this region of space. The researchers recognized that the missions, although launched 20 years apart, had collected complementary data. Voyager 1 and 2 had instruments that measured energetic ions as the craft crossed the heliosheath and exited the solar system. Cassini, meanwhile, was able to remotely observe energetic neutral atoms (ENAs) arriving in all directions from the heliosheath.

    These two phenomena are related: ENAs come from the heliosheath, where fast solar wind protons collide with neutral hydrogen atoms from interstellar space and “steal” an electron from the interlopers. The Voyager probes took in situ measurements of the parent heliosheath proton distributions as they passed through this region. Meanwhile, the protons with newly added electrons become ENAs and zip off in all directions.

    The synergy among the spacecrafts’ observations allowed the researchers to use Voyager data from the heliosheath to ground truth and calibrate ENA data from Cassini, which was more sensitive to lower energetic particles than Voyager was. Together, the spacecraft extended data on the intensity of both ENAs and ions to include a broader range of energies, which gave the team a window into the physics in the heliosheath as the solar wind and interstellar medium press against each other.

    The researchers found that in the energy range considered in their study (>5 kiloelectron volts), lower-energy ions with energies between about 5 and 24 kiloelectron volts played the largest role in maintaining the pressure balance inside the heliosheath. This allowed the team to calculate the strength of the magnetic field and the density of neutral hydrogen atoms in interstellar space—about 0.5 nanotesla and 0.12 per cubic centimeter, respectively.

    On the basis of calculations from Voyager 2 data, the researchers predict that the heliopause, the outer boundary of the heliosheath, is located roughly 18 billion kilometers from the Sun, or 119 times the distance from the Sun to the Earth—right where Voyager 2 found it in November 2018.

    Furthermore, the finding that the lower-energy ions dominate the pressure balance in the heliosheath means that space physicists will have to rethink their assumptions about the energy distribution of such particles in the heliosheath.

    See the full article here .


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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

  • richardmitnick 3:58 pm on February 17, 2019 Permalink | Reply
    Tags: Asgardia, , , , , Heliopause, , , , See the full blog post for images of all of the spacecraft involved and the Heliopause and Heliosphere, Which Spacecraft Will Reach Interstellar Space Next?   

    From Asgardia via Medium: “Which Spacecraft Will Reach Interstellar Space Next?” 

    From Asgardia




    NASA’s Voyager 2spacecraft reached interstellar space in December 2018, following in the footsteps of its sister, Voyager 1. Currently, only five spacecraft have been launched that can make such a grand exit, including the Voyagers. The other three are Pioneers 10 and 11, and New Horizons. Which one will make a great escape next?

    NASA/Voyager 2

    NASA/Voyager 1

    NASA Pioneer 10

    NASA Pioneer 11

    NASA/New Horizons spacecraft

    Reaching interstellar space is a milestone that is thought of as leaving the solar system by a specific definition. In 1990, the New York Times reported that Pioneer left the solar system when it flew past Neptune’s orbit. But that’s not what Voyager 2’s scientists used as their definition. Instead, the more recent measurements said the crossing of the sun’s heliopause, the theoretical boundary to its heliosphere, is the determining factor for entering interstellar space.

    The heliosphere is a bubble of charged particles that are created by and flows past the sun. It is used by scientists to mark where interstellar space starts.

    NASA Heliosphere

    However, the heliosphere is tricky, and there are many changes such as the sun’s 22-year solar cycle, the shrinking and growing with the solar wind, and stretching out behind the sun in the star’s direction of travel. It’s not something that can be measured easily from Earth. Thus, NASA’s Interstellar Boundary Explorer (IBEX) mission is trying to define the edges of the bubble remotely.

    Observations from the Voyager probes’ indicate that they’ve pierced this bubble. However, since researchers think the Oort Cloud also surrounds the sun, an area of icy bodies that is estimated to stretch from 1,000 to 100,000 astronomical units — far beyond the heliopause — the Voyager probes cannot be considered entirely outside the solar system. (One astronomical unit, or AU, is the distance between the Earth and the sun — 93 million miles, or 150 million kilometres).

    Oort cloud Image by TypePad, http://goo.gl/NWlQz6

    Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

    When Voyager 1 and 2 crossed the heliopause, their still-working particle instruments unveiled the historical events. The heliosphere functions as a shield, keeping out many of the higher-energy particles created by the cosmic rays generated by other stars.

    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

    By tracking both the low-energy particles found inside the solar system and the high-energy particles from outside of it, the instruments could reveal a sudden surge of cosmic rays alerting scientists that the spacecraft had left the solar system.

    The ever-changing nature of the heliosphere makes it impossible to tell when Pioneer 10 and 11 will enter interstellar space. It’s even possible that one of them may have already.

    As per NASA’s e-book Beyond Earth: A Chronicle of Deep Space Exploration, from Nov. 5, 2017, Pioneer 10 was approximately 118.824 AUs from Earth, farther than any craft besides Voyager 1. H(?), Although Pioneer 11 and the Voyager twins were all heading in the direction of the sun’s apparent travel, Pioneer 10 is headed toward the trailing side. 2017 research showed that the tail of the heliosphere is around 220 AU from the sun. Since Pioneer 10 travels about 2.5 AU/year, it will take Pioneer until roughly 2057–40 years — to reach the changing boundary.

    Pioneer 11 was thought to be approximately 97.6 AUs from Earth as of Nov. 5, 2017, according to the same e-book. Unlike its twin, the spacecraft is travelling in about the same direction as the Voyagers. Voyager 2 crossed into interstellar medium at approximately 120 AUs. Since Pioneer 11 is moving at 2.3 AU/year, it should reach interstellar space in about eight years, around 2027 — assuming the boundary doesn’t change, which it probably will.

    On Jan. 1, 2019, New Horizons made its most recent flyby of a solar system object, and it was launched much later than the other four. During this flyby, New Horizons was 43 AU from the sun. The mission’s principal investigator, Alan Stern, told Space.com that the spacecraft was travelling approximately 3.1 AU each year, or 31 AU in ten years. In another two decades, the spacecraft has a good chance of reaching interstellar space. If New Horizons crossed at Voyager 2’s same border (it won’t, but just consider as a baseline), it would make the trip in just under 24 years, in 2043. But it’s possible the ISM line will move inward, allowing it to cross sooner.

    Although there won’t be a direct confirmation of crossing the heliopause with the Pioneer spacecraft, it’s possible that New Horizons will still be working, and will give us a detailed study of interstellar space. The particle detectors that it holds are much more potent than the ones on Voyager, Stern said. Moreover, New Horizons holds a dust detector that would offer insight into the area beyond the heliosphere.

    However, whether or not they will still be functioning remains to be seen. As per Stern, power is the limiting factor. New Horizons runs off of decaying plutonium dioxide. Presently, the spacecraft has enough power to work until the late 2030s, said Stern, and it is currently in good working order.

    If in the unlikely event that the ever-changing heliosphere remains static Pioneer 11 will be the next to cross the heliopause in 2027, followed by New Horizons in 2043. Pioneer 10, the first of the five spacecraft to launch, will be the last to leave the heliosphere, in 2057. Once again, this assumes the extremely unrealistic chance that the heliopause remaining static for the next four decades.

    See the full article here .


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    About Medium

    Medium is an online publishing platform developed by Evan Williams, and launched in August 2012. It is owned by A Medium Corporation. The platform is an example of social journalism, having a hybrid collection of amateur and professional people and publications, or exclusive blogs or publishers on Medium, and is regularly regarded as a blog host.

    Williams developed Medium as a way to publish writings and documents longer than Twitter’s 140-character (now 280-character) maximum.

  • richardmitnick 9:37 am on December 10, 2018 Permalink | Reply
    Tags: , , , , , Heliopause, , , , , ,   

    From JPL-Caltech: “NASA’s Voyager 2 Probe Enters Interstellar Space” 

    NASA JPL Banner

    From JPL-Caltech

    Dec. 10, 2018

    Dwayne Brown
    Headquarters, Washington
    202-358-1726 / 301-286-6284

    Karen Fox
    Headquarters, Washington

    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.

    This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto.

    For the second time in history, a human-made object has reached the space between the stars. NASA’s Voyager 2 probe now has exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun.

    NASA/Voyager 2

    Members of NASA’s Voyager team will discuss the findings at a news conference at 11 a.m. EST (8 a.m. PST) today at the meeting of the American Geophysical Union (AGU) in Washington. The news conference will stream live on the agency’s website.

    Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.

    NASA/Voyager 1

    Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information – moving at the speed of light – takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.

    Artist’s concept of Voyager 2 with 9 facts listed around it. Image Credit: NASA

    The most compelling evidence of Voyager 2’s exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble – the heliosphere – that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.

    Animated gif showing the plasma data. Image Credit: NASA/JPL-Caltech

    “Working on Voyager makes me feel like an explorer, because everything we’re seeing is new,” said John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge. “Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we’re still seeing things that no one has seen before.”

    In addition to the plasma data, Voyager’s science team members have seen evidence from three other onboard instruments – the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer – that is consistent with the conclusion that Voyager 2 has crossed the heliopause. Voyager’s team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling.

    “There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.

    Together, the two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. Their observations complement data from NASA’s Interstellar Boundary Explorer (IBEX), a mission that is remotely sensing that boundary. NASA also is preparing an additional mission – the upcoming Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024 – to capitalize on the Voyagers’ observations.

    “Voyager has a very special place for us in our heliophysics fleet,” said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. “Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”

    While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won’t be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun’s gravity.

    Oort Cloud NASA

    The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.

    The Voyager probes are powered using heat from the decay of radioactive material, contained in a device called a radioisotope thermal generator (RTG). The power output of the RTGs diminishes by about four watts per year, which means that various parts of the Voyagers, including the cameras on both spacecraft, have been turned off over time to manage power.

    “I think we’re all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone,” said Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “This is what we’ve all been waiting for. Now we’re looking forward to what we’ll be able to learn from having both probes outside the heliopause.”

    Voyager 2 launched in 1977, 16 days before Voyager 1, and both have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. However, as the mission continued, additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 41 years, making Voyager 2 NASA’s longest running mission.

    The Voyager story has impacted not only generations of current and future scientists and engineers, but also Earth’s culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages.

    NASA Voyager Golden Record

    Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.

    Voyager’s mission controllers communicate with the probes using NASA’s Deep Space Network (DSN), a global system for communicating with interplanetary spacecraft. The DSN consists of three clusters of antennas in Goldstone, California; Madrid, Spain; and Canberra, Australia.

    NASA Deep Space Network dish, Goldstone, CA, USA

    NASA Canberra, AU, Deep Space Network

    NASA Deep Space Network Madrid Spain

    The Voyager Interstellar Mission is a part of NASA’s Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA’s Science Mission Directorate in Washington. JPL built and operates the twin Voyager spacecraft. NASA’s DSN, managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. The Commonwealth Scientific and Industrial Research Organisation, Australia’s national science agency, operates both the Canberra Deep Space Communication Complex, part of the DSN, and the Parkes Observatory, which NASA has been using to downlink data from Voyager 2 since Nov. 8.

    For more information about the Voyager mission, visit:


    More information about NASA’s Heliophysics missions is available online at:


    See the full article here .


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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge, on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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    NASA image

  • richardmitnick 11:38 am on March 14, 2018 Permalink | Reply
    Tags: , , , , , Heliopause, Modeling the Variable Heliopause Location   

    From AAS NOVA: “Modeling the Variable Heliopause Location” 



    14 March 2018
    Kerry Hensley

    Artist’s illustration demonstrating the distance traveled by Voyager 1. [NASA/JPL.]

    In 2012, Voyager 1 zipped across the heliopause. Five and a half years later, Voyager 2 still hasn’t followed its twin into interstellar space. Can models of the heliopause location help determine why?

    NASA/Voyager 1

    NASA/Voyager 2

    Artist’s conception of the heliosphere with the important structures and boundaries labeled. [NASA/Goddard/Walt Feimer.]

    How Far to the Heliopause?

    As our solar system travels through the galaxy, the solar outflow pushes against the surrounding interstellar medium, forming a bubble called the heliosphere. The edge of this bubble, the heliopause, is the outermost boundary of our solar system, where the solar wind and the interstellar medium meet. Since the solar outflow is highly variable, the heliopause is constantly moving — with the motion driven by changes in the Sun.

    NASA’s twin Voyager spacecraft were poised to cross the heliopause after completing their tour of the outer planets in the 1980s. In 2012, Voyager 1 registered a sharp increase in the density of interstellar particles, indicating that the spacecraft had passed out of the heliosphere and into the interstellar medium. The slower-moving Voyager 2 was set to pierce the heliopause along a different trajectory, but so far no measurements have shown that the spacecraft has bid farewell to our solar system.

    In a recent study, a team of scientists led by Haruichi Washimi (Kyushu University, Japan and CSPAR, University of Alabama-Huntsville) argues that models of the heliosphere can help explain this behavior. Because the heliopause location is controlled by factors that vary on many spatial and temporal scales, Washimi and collaborators turn to three-dimensional, time-dependent magnetohydrodynamics simulations of the heliosphere. In particular, they investigate how the position of the heliopause along the trajectories of Voyager 1 and Voyager 2 changes over time.

    Modeled location of the heliopause along the paths of Voyagers 1 (blue) and 2 (orange). Click for a closer look. The red star indicates the location at which Voyager 1 crossed the heliopause. The current location of Voyager 2 is marked with a red circle. [Washimi et al. 2017]

    A Time-Varying Barrier

    The authors consider the impact that solar flares, coronal mass ejections, and other disturbances in the solar outflow have on the heliopause distance. These solar disturbances intermingle as they travel outward to form what the authors call global merged interaction regions.

    Using their hydrodynamical simulations, Washimi and collaborators capture the complex behavior of the global merged interaction regions as they propagate through the termination shock and collide with the heliopause. Part of the shock is transmitted into the local interstellar medium, while part of it is reflected back toward and collides with the termination shock, which is pushed toward the Sun. This complex interplay of transmitted and reflected shocks — combined with the nonuniformity of the local interstellar medium — causes the heliopause location to vary dramatically in time as well as space.

    What Does this Mean for Voyager 2?

    Washimi and collaborators find that the location of the heliopause along the trajectories of Voyagers 1 and 2 has changed considerably over the past decade. In particular, they find that the heliopause has been pushed outward over the past few years due to an increase in the solar wind ram pressure. According to their simulations, Voyager 2 is currently traveling outward faster than the heliopause is advancing, which means that the spacecraft should soon cross the boundary — perhaps even this year — to become Earth’s second interstellar messenger.


    Haruichi Washimi et al 2017 ApJL 846 L9 http://iopscience.iop.org/article/10.3847/2041-8213/aa8556/meta

    Related journal articles
    See the full article for further references with links.

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

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