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  • richardmitnick 9:35 am on August 20, 2019 Permalink | Reply
    Tags: "Sampling the Space Between the Stars", , ENAs-energetic neutral atoms, , , Heliosheath, , NASA Voyager 1 and 2,   

    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

    1
    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 8:29 am on August 14, 2019 Permalink | Reply
    Tags: "A brief astronomical history of Saturn’s amazing rings", , , , , In the four centuries since the invention of the telescope rings have also been discovered around Jupiter Uranus and Neptune., NASA Voyager 1 and 2, Pioneer 11, , , The magnificent ring system of Saturn is between 10 meters and one kilometer thick., The shepherd moons Pan; Daphnis; Atlas; Pandora and Prometheus measuring between eight and 130 kilometers across quite literally shepherd the ring particles keeping them in their present orbits.   

    From The Conversation: “A brief astronomical history of Saturn’s amazing rings” 

    Conversation
    From The Conversation

    August 14, 2019
    Vahe Peroomian, University of Southern California

    1
    With giant Saturn hanging in the blackness and sheltering Cassini from the Sun’s blinding glare, the spacecraft viewed the rings as never before.

    Many dream of what they would do had they a time machine. Some would travel 100 million years back in time, when dinosaurs roamed the Earth. Not many, though, would think of taking a telescope with them, and if, having done so, observe Saturn and its rings.

    Whether our time-traveling astronomer would be able to observe Saturn’s rings is debatable. Have the rings, in some shape or form, existed since the beginnings of the solar system, 4.6 billion years ago, or are they a more recent addition? Had the rings even formed when the Chicxulub asteroid wiped out the dinosaurs?

    I am a space scientist with a passion for teaching physics and astronomy, and Saturn’s rings have always fascinated me as they tell the story of how the eyes of humanity were opened to the wonders of our solar system and the cosmos.

    Our view of Saturn evolves

    When Galileo first observed Saturn through his telescope in 1610, he was still basking in the fame of discovering the four moons of Jupiter. But Saturn perplexed him. Peering at the planet through his telescope, it first looked to him as a planet with two very large moons, then as a lone planet, and then again through his newer telescope, in 1616, as a planet with arms or handles.

    Four decades later, Giovanni Cassini first suggested that Saturn was a ringed planet, and what Galileo had seen were different views of Saturn’s rings. Because of the 27 degrees in the tilt of Saturn’s rotation axis relative to the plane of its orbit, the rings appear to tilt toward and away from Earth with the 29-year cycle of Saturn’s revolution about the Sun, giving humanity an ever-changing view of the rings.

    But what were the rings made of? Were they solid disks as some suggested? Or were they made up of smaller particles? As more structure became apparent in the rings, as more gaps were found, and as the motion of the rings about Saturn was observed, astronomers realized that the rings were not solid, and were perhaps made up of a large number of moonlets, or small moons. At the same time, estimates for the thickness of the rings went from Sir William Herschel’s 300 miles in 1789, to Audouin Dollfus’ much more precise estimate of less than two miles in 1966.

    Astronomers understanding of the rings changed dramatically with the Pioneer 11 and twin Voyager missions to Saturn.

    NASA Pioneer 11

    NASA/Voyager 1

    NASA/Voyager 2

    Voyager’s now famous photograph of the rings, backlit by the Sun, showed for the first time that what appeared as the vast A, B and C rings in fact comprised millions of smaller ringlets.

    2
    Voyager 2 false color image of Saturn’s B and C rings showing many ringlets. NASA

    The Cassini mission to Saturn, having spent over a decade orbiting the ringed giant, gave planetary scientists even more spectacular and surprising views.

    NASA/ESA/ASI Cassini-Huygens Spacecraft

    The magnificent ring system of Saturn is between 10 meters and one kilometer thick. The combined mass of its particles, which are 99.8% ice and most of which are less than one meter in size, is about 16 quadrillion tons, less than 0.02% the mass of Earth’s Moon, and less than half the mass of Saturn’s moon Mimas. This has led some scientists to speculate whether the rings are a result of the breakup of one of Saturn’s moons or the capture and breakup of a stray comet.

    The dynamic rings

    In the four centuries since the invention of the telescope, rings have also been discovered around Jupiter, Uranus and Neptune, the giant planets of our solar system. The reason why the giant planets are adorned with rings and Earth and the other rocky planets are not was first proposed by Eduard Roche, a French astronomer in 1849.

    A moon and its planet are always in a gravitational dance. Earth’s moon, by pulling on opposite sides of the Earth, causes the ocean tides. Tidal forces also affect planetary moons. If a moon ventures too close to a planet, these forces can overcome the gravitational “glue” holding the moon together and tear it apart. This causes the moon to break up and spread along its original orbit, forming a ring.

    The Roche limit, the minimum safe distance for a moon’s orbit, is approximately 2.5 times the planet’s radius from the planet’s center. For enormous Saturn, this is a distance of 87,000 kilometers above its cloud tops and matches the location of Saturn’s outer F ring. For Earth, this distance is less than 10,000 kilometers above its surface. An asteroid or comet would have to venture very close to the Earth to be torn apart by tidal forces and form a ring around the Earth. Our own Moon is a very safe 380,000 kilometers away.

    3
    NASA’s Cassini spacecraft about to make one of its dives between Saturn and its innermost rings as part of the mission’s grand finale. NASA/JPL-Caltech

    The thinness of planetary rings is caused by their ever-changing nature. A ring particle whose orbit is tilted with respect to the rest of the ring will eventually collide with other ring particles. In doing so, it will lose energy and settle into the plane of the ring. Over millions of years, all such errant particles either fall away or get in line, leaving only the very thin ring system people observe today.

    During the last year of its mission, the Cassini spacecraft dived repeatedly through the 7,000 kilometer gap between the clouds of Saturn and its inner rings. These unprecedented observations made one fact very clear: The rings are constantly changing. Individual particles in the rings are continually jostled by each other. Ring particles are steadily raining down onto Saturn.

    The shepherd moons Pan, Daphnis, Atlas, Pandora and Prometheus, measuring between eight and 130 kilometers across, quite literally shepherd the ring particles, keeping them in their present orbits. Density waves, caused by the motion of shepherd moons within the rings, jostle and reshape the rings. Small moonlets are forming from ring particles that coalesce together. All this indicates that the rings are ephemeral. Every second up to 40 tons of ice from the rings rain down on Saturn’s atmosphere. That means the rings may last only several tens to hundreds of millions of years.

    Could a time-traveling astronomer have seen the rings 100 million years ago? One indicator for the age of the rings is their dustiness. Objects exposed to the dust permeating our solar system for long periods of time grow dustier and darker.

    Saturn’s rings are extremely bright and dust-free, seeming to indicate that they formed anywhere from 10 to 100 million years ago, if astronomers’ understanding of how icy particles gather dust is correct. One thing is for certain. The rings our time-traveling astronaut would have seen would have looked very different from the way they do today.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Conversation launched as a pilot project in October 2014. It is an independent source of news and views from the academic and research community, delivered direct to the public.
    Our team of professional editors work with university and research institute experts to unlock their knowledge for use by the wider public.
    Access to independent, high quality, authenticated, explanatory journalism underpins a functioning democracy. Our aim is to promote better understanding of current affairs and complex issues. And hopefully allow for a better quality of public discourse and conversation.

     
  • richardmitnick 9:37 am on December 10, 2018 Permalink | Reply
    Tags: , , , , , , , , NASA Voyager 1 and 2, , ,   

    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
    dwayne.c.brown@nasa.gov

    Karen Fox
    Headquarters, Washington
    301-286-6284
    karen.c.fox@nasa.gov

    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.
    626-808-2469
    calla.e.cofield@jpl.nasa.gov

    1
    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.

    2
    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.

    3
    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:

    https://www.nasa.gov/voyager

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

    https://www.nasa.gov/sunearth

    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.

    Caltech Logo

    NASA image

     
  • richardmitnick 8:54 am on August 12, 2018 Permalink | Reply
    Tags: , , , , NASA Voyager 1 and 2, , New Horizons may have seen a glow at the solar system’s edge,   

    From Science News: “New Horizons may have seen a glow at the solar system’s edge” 

    From Science News

    August 9, 2018
    Lisa Grossman

    The ultraviolet signal may mark a wall of hydrogen where the sun’s influence wanes.

    1
    HELLO FROM THE OTHER SIDE The sun’s journey through the galaxy may build a wall of hydrogen near the edge of the solar system (curved line to the left of this illustration). The New Horizons spacecraft may have seen evidence of just such a wall. Adler Planetarium/IBEX/NASA

    The New Horizons spacecraft has spotted an ultraviolet glow that seems to emanate from near the edge of the solar system.

    NASA New Horizons spacecraft

    That glow may come from a long-sought wall of hydrogen that represents where the sun’s influence wanes, the New Horizons team reports online August 7 in Geophysical Research Letters.

    “We’re seeing the threshold between being in the solar neighborhood and being in the galaxy,” says team member Leslie Young of the Southwest Research Institute, based in Boulder, Colo.

    Even before New Horizons flew past Pluto in 2015 (SN: 8/8/15, p. 6), the spacecraft was scanning the sky with its ultraviolet telescope to look for signs of the hydrogen wall. As the sun moves through the galaxy, it produces a constant stream of charged particles called the solar wind, which inflates a bubble around the solar system called the heliosphere. Just beyond the edge of that bubble, around 100 times farther from the sun than the Earth, uncharged hydrogen atoms in interstellar space should slow when they collide with solar wind particles. That build-up of hydrogen, or wall, should scatter ultraviolet light in a distinctive way.

    The two Voyager spacecraft saw signs of such light scattering 30 years ago.

    NASA/Voyager 1

    NASA/Voyager 2


    One of those craft has since exited the heliosphere and punched into interstellar space (SN: 10/19/13, p. 19).

    New Horizons is the first spacecraft in a position to double-check the Voyagers’ observations. It scanned the ultraviolet sky seven times from 2007 to 2017, space scientist Randy Gladstone of the Southwest Research Institute in San Antonio and colleagues report. As the spacecraft travelled, it saw the ultraviolet light change in a way that supports the decades-old observations. All three spacecraft saw more ultraviolet light farther from the sun than expected if there is no wall. But the team cautions that the light could also be from an unknown source farther away in the galaxy.

    “It’s really exciting if these data are able to distinguish the hydrogen wall,” says space scientist David McComas of Princeton University, who was not involved in the new work. That could help figure out the shape and variability of the solar system’s boundary (SN: 5/27/17, p. 15).

    After New Horizons flies past the outer solar system object Ultima Thule on New Year’s Day 2019 (SN Online: 3/14/18), the spacecraft will continue to look for the wall about twice each year until the mission’s end, hopefully 10 to 15 years from now, Gladstone says.

    If the ultraviolet light drops off at some point, then New Horizons may have left the wall in its rear view mirror. But if the light never fades, then its source could be farther ahead — coming from somewhere deeper in space, says team member Wayne Pryor of Central Arizona College in Coolidge.

    See the full article here .


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