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  • richardmitnick 9:27 am on September 17, 2014 Permalink | Reply
    Tags: , , , , , NASA Voyager,   

    From NOVA: “Chasing the Edge of the Solar System” Old But Worth a Look 



    Tue, 09 Apr 2013
    David McComas

    For most of its lifetime, Voyager 1 has been traveling through uncharted territory. Initially launched to study the outer planets, Voyager 1 has soldiered on past Jupiter and Saturn and on to the outer edges of the solar system. It’s currently the farthest human-made object from Earth, but when will it be the first spacecraft to travel between the stars? Well, we won’t know until we answer two more fundamental questions: Where does our solar system end and the rest of the space between the stars begin? And if you were at the “edge” of our solar system, how would you know you had left? Recent scientific discussions on the Voyager spacecraft missions have captivated many people. And as the scientific debate swirled around the internet in near-real time, it became clear that these questions are not easy to answer. Voyager spacecraft
    The identical Voyager 1 and Voyager 2 are currently probing the farthest reaches of the solar system.

    NASA Voyager 2
    NASA/Voyager 2

    As the Principal Investigator for NASA’s Interstellar Boundary Explorer, or IBEX, spacecraft, I lead a team that is also studying this last frontier of our solar system. Data from IBEX complements the Voyager spacecraft—both missions are working together to find the very farthest reaches of the solar system. Unlike the Voyager spacecraft, which are careening out into interstellar space, IBEX orbits the Earth, collecting particles that have traveled in from the solar system’s boundary region and beyond. From those particles, we can determine many things, including what the boundary is like and what, exactly, is happening out there.


    More Than Planets

    Most everyone knows our solar system is composed of small solid objects orbiting the Sun—planets, comets, and asteroids. But there’s more to it than that. Our Sun continuously emits a “wind” of material outward in all directions, typically at speeds of about a million miles per hour (1.6 million kilometers per hour). The solar wind is composed mostly of charged particles, such as electrons and protons. It also carries the Sun’s magnetic field. As the solar wind streams away from the Sun, it races out past all the planets, past Pluto, and toward the space between the stars more than 10 billion miles away. We tend to think of that space as empty, but it’s not. Rather, it contains cold hydrogen gas, dust, ionized gas, and traces of other material. Called the interstellar medium, it’s a very thin mix that comes from exploded stars and the stellar wind of other stars. When the magnetic fields of the solar wind hit the magnetic fields of the interstellar medium, they do not intermix. The expanding solar wind pushes against the interstellar medium, clearing out a cavity in interstellar space known as the heliosphere. The boundary of that bubble is where the solar wind’s strength exactly matches the pressure of the interstellar medium. We call it the heliopause, and it’s often considered to be the very outer edge of our solar system.

    The Heliopause.

    A few things about the heliopause: It isn’t an impermeable wall. Instead, it’s more like the edge of a forest clearing—the boundary is well defined, but easily negotiated. It’s also shaped more like a drop of water than a uniform sphere. That’s because our entire heliosphere, which contains our Sun, the planets, and everything else in our solar system, is moving through the interstellar medium at about 50,000 miles per hour (80,000 kilometers per hour). That motion creates a wake in the interstellar medium, much like a boat moving through water. As the solar system travels through the interstellar medium the heliopause is closest at the “front,” or the foremost point in the direction in which our solar system is traveling. At that point, the heliopause is still over 10 billion miles, or 16 billion kilometers, from the Sun.

    Heliosphere and heliopause

    As solar wind pushes out against the interestellar medium, it creates a bubble known as the heliosphere; the boundary between the two is known as the heliopause. The termination shock is where the solar wind slows as it presses against more of the interstellar medium, which also raises the plasma’s temperature. The bow wave is where the interstellar medium material piles up in front of our heliosphere, similar to water in front of a moving boat
    At least, that’s our best guess. We don’t know exactly where the boundary is or what it’s like. That’s what the IBEX and Voyager missions are trying to find out. IBEX lets us peer into the boundaries of our solar system to get a better idea of what it’s like and what’s happening there. However, because IBEX orbits the Earth, we cannot use it to mark where the boundary is located. That’s where Voyager 1 and 2 come in. Currently, they are directly sampling the boundary region. Several of the instruments on Voyager 1 and 2 are no longer working, including the cameras used to snap the stunning fly-by photos of Jupiter, Saturn, Uranus, and Neptune, but others that detect charged particles and magnetic fields are still gathering data. Both Voyagers are traveling in roughly the same direction as our solar system through the interstellar medium. We expect Voyager 1, the quicker and farther out of the two, to reach the heliopause first. Currently, it’s just over 11 billion miles, or 18 billion kilometers, from the Sun. This is so distant that radio signals from Voyager 1, which are traveling at the speed of light, take 17 hours to reach Earth.

    Three Criteria

    Before we can declare that Voyager 1 has crossed the heliopause, we are waiting to observe three main changes:

    A decrease in highly energetic charged particles from inside our heliosphere,
    An increase in highly energetic charged particles from outside our heliosphere,
    And a change in the strength and direction of the magnetic field, matching that outside the heliosphere.

    Voyager 1 observed the first two in late 2012, and IBEX has provided what are likely the best observations of the third. By using IBEX to look at particles that have traveled in from outside the heliosphere, we have an idea of the direction of the magnetic field beyond the solar system, and it’s very different from the Sun’s, which is carried out by the solar wind. So far Voyager 1 hasn’t observed this change direction of the magnetic field. That’s why we don’t think that Voyager 1 has crossed the heliopause—yet.

    The IBEX satellite orbits the Earth, capturing particles that have traveled into the solar system from beyond the heliosphere.
    Now, Voyager 1 has clearly passed into a new region of space, one that we have not detected before. Every new bit of data coming from the venerable spacecraft is teaching us more about this uncharted territory. All of this information is new, and we are learning more every day. So, do we know when Voyager 1 will cross the heliopause? We really have no idea. And that’s part of the fun. But learning about the edge of space is more than just an esoteric pursuit. Our heliosphere is a protective cocoon, a crucial layer of shielding against dangerous charged particles, known as galactic cosmic rays, that are harmful to living things. Understanding it will help us understand how the heliosphere has protected our solar system, enabling life to flourish on this planet we call home. And someday, that knowledge will help us prepare for our first voyage beyond the protective cocoon of the solar system, when we step across the threshold and venture into deep space.

    See the full article here.

    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

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  • richardmitnick 8:51 am on July 31, 2014 Permalink | Reply
    Tags: , , , , , NASA Voyager   

    From SPACE.com: “How Far Away is Neptune?” 


    December 14, 2012
    Nola Taylor Redd

    The ice giant Neptune is the eighth and most distant planet from the sun. Since its discovery, only one Neptunian year has passed.

    On June 25, 2011, Neptune arrived at the same location in space where it was discovered 165 years earlier. To commemorate the event, NASA’s Hubble Space Telescope took “anniversary pictures” of the blue-green giant planet.
    Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

    How far is Neptune from Earth?

    The distance from one planet to another is constantly shifting because both bodies are moving through space. When Neptune and Earth line up on the same side of the sun, at their closest, they are only 2.7 billion miles (4.3 billon kilometers) apart. But when the planets are on opposite sides of the sun, they can put as many as 2.9 billion miles (4.7 billion km) between them.

    Neptune’s extreme distance made it the last full-size planet to be discovered. Unlike Uranus, it was found primarily by pouring over mathematical formulas rather than peering through a telescope. Astronomers had noticed that the recently-discovered Uranus had some orbital oddities that could not be explained. John Couch Adams and Urbain Le Verrier independently calculated the planet’s orbit between 1845 and 1846, and several astronomers began to search for the proposed planet. On September 23, 1846, the icy body was found within one degree of Le Verrier’s predictions and 12 degrees from where Adams suggested it would travel. This prompted discussion over who should be credited with the discovery, but ultimately both men were recognized for their roles.

    The planet was spotted in 1612 and 1613 by Galileo Galilei. Unfortunately, the Italian astronomer made his observations when Neptune had just begun its backward, or retrograde, motion across the sky. Planets that lie farther from Earth occasionally appear to move backward when our planet passes them in their orbit. The enormous distance to Neptune meant that the motion was too small to record in Galileo’s early telescope, resulting in his mischaracterization.

    How far is Neptune from the sun?

    Like all planets, Neptune orbits the sun in a stretched-out circle known as an ellipse. This means that its distance from the star is constantly changing. When the icy planet is closest to the sun, it lies “only” 2.77 billion miles (4.46 billion km). At its farthest, it passes 2.82 billion miles (4.54 billion km) from the star.

    Although Neptune is the eighth most distant planet, it was not always. The dwarf planet Pluto occasionally dips inside of Neptune’s orbit. Thus, when Pluto was classified as a planet, it was sometimes the eighth most distant planet while Neptune was the ninth. The two bodies will never collide, however, because for every three trips Neptune makes around the sun, Pluto takes exactly two, which keeps them from every traveling through the same area at the same time.

    Neptune takes 164.79 Earth-years to travel around the sun. On July 11, 2011, Neptune had completed one full orbit since its discovery. It was not in the same spot in the sky, however, because Earth lay at a different point in its orbit.

    Although the most distant planet now, it is possible the Neptune was not always so far away. The amount of gas and ice needed to form the giant planet is greater than fits current models. Some scientists suggest that Neptune may have formed closer to the sun, then migrated out to its present location over time.

    How long does it take to reach Neptune?

    The constant motion of Neptune and Earth is the biggest force that determines how long it takes to travel between the two planets. It would take a satellite longer to reach Neptune if it was launched when the two planets were on opposite sides of the sun instead of the same time.

    The only spacecraft to visit Neptune was Voyager 2. Launched on August 20, 1977, it made its closest approach to the planet on August 25, 1989, after a dozen years of travel. Voyager 2 observed Neptune’s “Great Dark Spot,” a series of short-term storms in Neptune’s atmosphere. The dark spot is approximately the same size as Earth, and is thought to be a hole in Neptune’s methane clouds.

    NASA Voyager 2
    NASA/Voyager 2

    No other craft has traveled to the planet. However, NASA’s New Horizons, launched January 19, 2006, will pass through Neptune’s orbit on its way to visit Pluto and the Kuiper Belt. The spacecraft will travel through the planet’s orbit in August of 2014, after eight years of traveling.

    NASA New Horizons spacecraft

    kuiper belt
    Kuiper Belt

    See the full article here.

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  • richardmitnick 10:11 am on February 13, 2014 Permalink | Reply
    Tags: , , , , , , NASA Voyager   

    From NASA/JPL at Caltech: “Largest Solar System Moon Detailed in Geologic Map” 

    February 12, 2014
    Jia-Rui Cook 818-354-0850
    Jet Propulsion Laboratory, Pasadena,
    Calif. jccook@jpl.nasa.gov

    More than 400 years after its discovery by astronomer Galileo Galilei, the largest moon in the solar system – Jupiter’s moon Ganymede – has finally claimed a spot on the map.

    To present the best information in a single view of Jupiter’s moon Ganymede, a global image mosaic was assembled, incorporating the best available imagery from NASA’s Voyager 1 and 2 spacecraft and NASA’s Galileo spacecraft. USGS Astrogeology Science Center/Wheaton/NASA/JPL-Caltech

    A group of scientists led by Geoffrey Collins of Wheaton College has produced the first global geologic map of Ganymede, Jupiter’s seventh moon. The map combines the best images obtained during flybys conducted by NASA’s Voyager 1 and 2 spacecraft (1979) and Galileo orbiter (1995 to 2003) and is now published by the U. S. Geological Survey as a global map. It technically illustrates the varied geologic character of Ganymede’s surface and is the first global, geologic map of this icy, outer-planet moon. The geologic map of Ganymede is available for download at: http://www.jpl.nasa.gov/spaceimages/details.php?id=pia17902 ).

    NASA Galileo

    NASA Voyager

    “This map illustrates the incredible variety of geological features on Ganymede and helps to make order from the apparent chaos of its complex surface,” said Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “This map is helping planetary scientists to decipher the evolution of this icy world and will aid in upcoming spacecraft observations.”

    The European Space Agency’s Jupiter Icy Moons Explorer mission is slated to be orbiting Ganymede around 2032. NASA is contributing a U.S.-led instrument and hardware for two European-led instruments for the mission.

    Since its discovery in January 1610, Ganymede has been the focus of repeated observation, first by Earth-based telescopes, and later by the flyby missions and spacecraft orbiting Jupiter. These studies depict a complex, icy world whose surface is characterized by the striking contrast between its two major terrain types: the dark, very old, highly cratered regions, and the lighter, somewhat younger (but still very old) regions marked with an extensive array of grooves and ridges.

    According to the scientists who have constructed this map, three major geologic periods have been identified for Ganymede that involve the dominance of impact cratering, then tectonic upheaval, followed by a decline in geologic activity. The map, which illustrates surface features, such as furrows, grooves and impact craters, allows scientists to decipher distinct geologic time periods for an object in the outer solar system for the first time.

    “The highly detailed, colorful map confirmed a number of outstanding scientific hypotheses regarding Ganymede’s geologic history, and also disproved others,” said Baerbel Lucchitta, scientist emeritus at the U.S. Geological Survey in Flagstaff, Ariz., who has been involved with geologic mapping of Ganymede since 1980. “For example, the more detailed Galileo images showed that cryovolcanism, or the creation of volcanoes that erupt water and ice, is very rare on Ganymede.”

    The Ganymede global geologic map will enable researchers to compare the geologic characters of other icy satellite moons, because almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede.

    “The surface of Ganymede is more than half as large as all the land area on Earth, so there is a wide diversity of locations to choose from,” Collins said. “Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity.”

    Amateur astronomers can observe Ganymede (with binoculars) in the evening sky this month, as Jupiter is in opposition and easily visible.

    See the full article here.

    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 [1], 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

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