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  • richardmitnick 8:19 am on March 22, 2017 Permalink | Reply
    Tags: , CHAMP Lithosphere, , Ironing out the mystery of Earth’s magnetic field,   

    From ESA: “Unravelling Earth’s magnetic field” 

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    European Space Agency

    21 March 2017

    ESA’s Swarm satellites are seeing fine details in one of the most difficult layers of Earth’s magnetic field to unpick – as well as our planet’s magnetic history imprinted on Earth’s crust.


    ESA/Swarm

    Earth’s magnetic field can be thought of as a huge cocoon, protecting us from cosmic radiation and charged particles that bombard our planet in solar wind. Without it, life as we know it would not exist.


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

    Most of the field is generated at depths greater than 3000 km by the movement of molten iron in the outer core. The remaining 6% is partly due to electrical currents in space surrounding Earth, and partly due to magnetised rocks in the upper lithosphere – the rigid outer part of Earth, consisting of the crust and upper mantle.

    Although this ‘lithospheric magnetic field’ is very weak and therefore difficult to detect from space, the Swarm trio is able to map its magnetic signals. After three years of collecting data, the highest resolution map of this field from space to date has been released.

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    “By combining Swarm measurements with historical data from the German CHAMP satellite, and using a new modelling technique, it was possible to extract the tiny magnetic signals of crustal magnetisation,” explained Nils Olsen from the Technical University of Denmark, one of the scientists behind the new map.

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    Lithosphere From CHAMP. http://geomag.org/info/lithosphere.html

    ESA’s Swarm mission manager, Rune Floberghagen, added: “Understanding the crust of our home planet is no easy feat. We can’t simply drill through it to measure its structure, composition and history.

    “Measurements from space have great value as they offer a sharp global view on the magnetic structure of our planet’s rigid outer shell.”

    Presented at this week’s Swarm Science Meeting in Canada, the new map shows detailed variations in this field more precisely than previous satellite-based reconstructions, caused by geological structures in Earth’s crust.

    One of these anomalies occurs in Central African Republic, centred around the city of Bangui, where the magnetic field is significantly sharper and stronger. The cause for this anomaly is still unknown, but some scientists speculate that it may be the result of a meteorite impact more than 540 million years ago.

    The magnetic field is in a permanent state of flux. Magnetic north wanders, and every few hundred thousand years the polarity flips so that a compass would point south instead of north.

    When new crust is generated through volcanic activity, mainly along the ocean floor, iron-rich minerals in the solidifying magma are oriented towards magnetic north, thus capturing a ‘snapshot’ of the magnetic field in the state it was in when the rocks cooled.

    Since magnetic poles flip back and forth over time, the solidified minerals form ‘stripes’ on the seafloor and provide a record of Earth’s magnetic history.

    The latest map from Swarm gives us an unprecedented global view of the magnetic stripes associated with plate tectonics reflected in the mid-oceanic ridges in the oceans.

    “These magnetic stripes are evidence of pole reversals and analysing the magnetic imprints of the ocean floor allows the reconstruction of past core field changes. They also help to investigate tectonic plate motions,” said Dhananjay Ravat from the University of Kentucky in the USA.

    “The new map defines magnetic field features down to about 250 km and will help investigate geology and temperatures in Earth’s lithosphere.”

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 12:56 pm on June 2, 2016 Permalink | Reply
    Tags: , , , Ironing out the mystery of Earth’s magnetic field   

    From DESY: “Ironing out the mystery of Earth’s magnetic field” 

    DESY
    DESY

    2016/06/01
    No writer credit found

    Scientists directly measure thermal conductivity of iron at planetary core conditions for the first time.

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    A cross-section of the earth with the field lines of the geomagnetic field (as simulated with the Glatzmaier-Roberts geodynamo model http://www.es.ucsc.edu/~glatz/geodynamo.html ). Illustration: DESY

    The earth’s magnetic field has been existing for at least 3.4 billion years thanks to the low heat conduction capability of iron in the planet’s core. This is the result of the first direct measurement of the thermal conductivity of iron at pressures and temperatures corresponding to planetary core conditions. DESY scientist Zuzana Konôpková and her colleagues present their study* in the scientific journal Nature. The results could resolve a recent debate about the so-called geodynamo paradox.

    The geodynamo generating the earth’s magnetic field is fed on convection in the iron-rich outer core of our planet that stirs the molten, electrically conducting material like boiling water in a pot. Combined with the rotation of the earth, a dynamo effect sets in, giving rise to the geomagnetic field. “The magnetic field shields us from harmful high-energy particles from space, the so-called cosmic radiation, and its existence is one of the things that make our planet habitable,” explains Konôpková.

    The strength of the convection in the outer core depends on the heat transferred from the core to the earth’s lower mantle and on the thermal conductivity of iron in the outer core. If a lot of heat is transferred via conduction, there is not much energy left to drive convection – and with it the earths’s dynamo. Low thermal conductivity implies stronger convection, making the geodynamo more likely to operate. “We measured the thermal conductivity of iron because we wanted to know what the energy budget of the core is to drive the dynamo,” says Konôpková. “Generation and maintenance of our planet’s magnetic field strongly depend on the thermal dynamics of the core.”

    Measurements of thermal conductivity at relevant conditions proved to be difficult in the past. Recent theoretical calculations postulated a quite high thermal conductivity of up to 150 Watts per meter per Kelvin (150 W/m/K) of iron in the earth’s core. Such a high thermal conductivity would reduce the chances of the geodynamo starting up.

    According to numerical models, a high thermal conductivity would have allowed the geodynamo effect to be supported only rather recently in the earth’s history, about one billion years ago or so. However, the existence of the geomagnetic field can be traced back at least 3.4 billion years. This geodynamo paradox has puzzled scientists. “There’s been a fierce debate among geophysicists because with such a large thermal conductivity, it becomes hard to explain the history of the geomagnetic field which is recorded in ancient rocks”, says Konôpková.

    The physicists used a specially designed pressure cell that allows to compress samples between two diamond anvils and to heat them simultaneously with infrared lasers, shining right through the diamonds. Konôpková teamed up with Stewart McWilliams and Natalia Gómez-Pérez from the University of Edinburgh and Alexander Goncharov from the Carnegie Institution in Washington DC to measure the thermal conductivity of iron at high pressure and high temperature conditions in Goncharov’s lab.

    “We compressed a thin foil of iron in the diamond anvil cell to up to 130 Giga-Pascals, which is more than a million times the atmospheric pressure and corresponds to approximately the pressure at the earth’s core-mantle boundary,” explains Konôpková. “Simultaneously we heated up the foil to up to 2700 degrees Celsius with two continuous infrared laser beams, shining through the diamonds. Finally, we used a third laser to send a low power pulse to one side of the foil to create a thermal perturbation and measured the temperature evolution from both sides of the foil with an optical streak camera.” This way the scientists could watch the heat pulse travelling through the iron.

    These measurements were conducted at several pressures and temperatures to cover different conditions of planetary interiors and to obtain a systematic investigation of the thermal conductivity as a function of pressure and temperature. “Our results strongly contradict the theoretical calculations,” reports Konôpková. “We found very low values of thermal conductivity, about 18 to 44 Watts per meter per Kelvin, which can resolve the paradox and make the geodynamo operable since the early ages of the earth.”

    *Science paper:
    Direct measurement of thermal conductivity in solid iron at planetary core conditions

    See the full article here .

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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
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