query: which layer of the earth is responsible for generating the earth magnetic field

pos: Earth's magnetic field pole, located near Greenland in the northern hemisphere, is actually the south pole of the Earth's magnetic field, and the South geomagnetic pole is the north pole. The magnetic field is generated by electric currents due to the motion of convection currents of molten iron in the Earth's outer core driven by heat escaping from the core, a natural process called a geodynamo. While the North and South magnetic poles are usually located near the geographic poles, they can wander widely over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals

pos: Earth science shielding some of the Earth's surface from cosmic rays—of which are often incorrectly thought to be deflected by the magnetic field. The magnetic field—created by the internal motions of the core—produces the magnetosphere which protects the Earth's atmosphere from the solar wind. As the Earth is 4.5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. An electromagnet is a magnet that is created by an electric current. The Earth has a solid iron inner core surrounded by fluid outer core that convects; therefore, the Earth is an electromagnet. The motion of

pos: Dynamo theory of the Earth. However, this hypothesis, which was initially proposed by Joseph Larmor in 1919, has been modified due to extensive studies of magnetic secular variation, paleomagnetism (including polarity reversals), seismology, and the solar system's abundance of elements. Also, the application of the theories of Carl Friedrich Gauss to magnetic observations showed that Earth's magnetic field had an internal, rather than external, origin. There are three requisites for a dynamo to operate: In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core. A requirement for the

pos: Geomagnetic pole Geomagnetic pole The geomagnetic poles are antipodal points where the axis of a best-fitting dipole intersects the surface of Earth. This theoretical dipole is equivalent to a powerful bar magnet at the center of Earth and comes closer than any other model to accounting for the magnetic field observed at Earth's surface. In contrast, the magnetic poles of the actual Earth are not antipodal; that is, the line on which they lie does not pass through Earth's center. Owing to motion of fluid in the Earth's outer core, the actual magnetic poles are constantly moving. However, over thousands of years

pos: Magnetosphere of Saturn hydrogen in its outer core. Like Earth, Saturn's magnetic field is mostly a dipole, with north and south poles at the ends of a single magnetic axis. On Saturn, like on Jupiter, the north magnetic pole is located in the northern hemisphere, and the south magnetic pole lies in the southern hemisphere, so that magnetic field lines point away from the north pole and towards the south pole. This is reversed compared to the Earth, where the north magnetic pole lies in the southern hemisphere. Saturn's magnetic field also has quadrupole, octupole and higher components, though they are much weaker

pos: Magnetic field quantum description mentioned here. However, under most everyday circumstances, the difference between the two theories is negligible. The Earth's magnetic field is produced by convection of a liquid iron alloy in the outer core. In a dynamo process, the movements drive a feedback process in which electric currents create electric and magnetic fields that in turn act on the currents. The field at the surface of the Earth is approximately the same as if a giant bar magnet were positioned at the center of the Earth and tilted at an angle of about 11° off the rotational axis of the

pos: Structure of the Earth certain normally oxyphile elements existing either partially or wholly in the alloy portion that corresponds to the core of Earth. Dynamo theory suggests that convection in the outer core, combined with the Coriolis effect, gives rise to Earth's magnetic field. The solid inner core is too hot to hold a permanent magnetic field (see Curie temperature) but probably acts to stabilize the magnetic field generated by the liquid outer core. The average magnetic field strength in Earth's outer core is estimated to be 25 Gauss (2.5 mT), 50 times stronger than the magnetic field at the surface. Recent evidence has

pos: Dynamo theory Earth's magnetism, proposed that this magnetic field resulted from electric currents induced in the fluid outer core of the Earth. He revealed the history of the Earth's magnetic field through pioneering the study of the magnetic orientation of minerals in rocks. In order to maintain the magnetic field against ohmic decay (which would occur for the dipole field in 20,000 years), the outer core must be convecting. The convection is likely some combination of thermal and compositional convection. The mantle controls the rate at which heat is extracted from the core. Heat sources include gravitational energy released by the compression

pos: Dynamo theory that the magnetic field direction cannot be inferred from this approximation (at least not its sign) as it appears squared, and is, indeed, sometimes reversed, though in general it lies on a similar axis to that of formula_40. For earth outer core, "ρ" is approximately 10 kg/m, "Ω"=2π/day = 7.3x10 seconds and "σ" is approximately 10Ωm. This gives 2.7x10 Tesla. The magnetic field of a magnetic dipole has an inverse cubic dependence in distance, so its order of magnitude at the earth surface can be approximated by multiplying the above result with ("R"/"R") = (2890/6370) = 0.093, giving 2.5x10 Tesla,

neg: Earth's magnetic field the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation. The Earth's magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the

neg: Saturn layer of liquid hydrogen and liquid helium, and finally a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's. The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach , higher than on Jupiter, but

neg: Aurora (see also [[Birkeland current]]s). The Earth is constantly immersed in the [[solar wind]], a rarefied flow of hot plasma (a gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree temperature of the Sun's outermost layer, the [[corona]]. The solar wind reaches Earth with a velocity typically around 400 km/s, a density of around 5 ions/cm and a magnetic field intensity of around 2–5 nT (for comparison, Earth's surface field is typically 30,000–50,000 nT). During [[Geomagnetic storm|magnetic storms]], in particular, flows can be several times faster; the [[interplanetary magnetic field]] (IMF)

neg: Atmosphere of Venus and downwell. Unlike Earth, Venus lacks a magnetic field. Its ionosphere separates the atmosphere from outer space and the solar wind. This ionised layer excludes the solar magnetic field, giving Venus a distinct magnetic environment. This is considered Venus's "induced magnetosphere". Lighter gases, including water vapour, are continuously blown away by the solar wind through the induced magnetotail. It is speculated that the atmosphere of Venus up to around 4 billion years ago was more like that of the Earth with liquid water on the surface. A runaway greenhouse effect may have been caused by the evaporation of the surface

neg: L-shell L-shell The L-shell, L-value, or McIlwain L-parameter (after Carl E. McIlwain) is a parameter describing a particular set of planetary magnetic field lines. Colloquially, L-value often describes the set of magnetic field lines which cross the Earth's magnetic equator at a number of Earth-radii equal to the L-value. For example, "formula_1" describes the set of the Earth's magnetic field lines which cross the Earth's magnetic equator two earth radii from the center of the Earth. L-shell parameters can also describe the magnetic fields of other planets. In such cases, the parameter is renormalized for that planet's radius and magnetic field

neg: History of geophysics the conductive molten metal beneath the Earth's crust, or the Earth's dynamo, is responsible for the existence of the magnetic field. The interaction of the magnetic field and solar radiation has an impact on how much radiation reaches the surface of Earth and the integrity of the atmosphere. It has been found that the magnetic poles of the Earth have reversed several times, allowing researchers to get an idea of the surface conditions of the planet at that time. The cause of the magnetic poles being reversed is unknown, and the intervals of change vary and do not show a

neg: Magnetic field information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass. Although magnets and magnetism were studied much earlier, the research of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field on the surface of a spherical magnet using iron needles. Noting that the resulting field lines crossed at two points he named those points 'poles' in analogy to Earth's poles. He also clearly articulated the

neg: Magnetocrystalline anisotropy great influence on industrial uses of ferromagnetic materials. Materials with high magnetic anisotropy usually have high coercivity, that is, they are hard to demagnetize. These are called "hard" ferromagnetic materials and are used to make permanent magnets. For example, the high anisotropy of rare-earth metals is mainly responsible for the strength of rare-earth magnets. During manufacture of magnets, a powerful magnetic field aligns the microcrystalline grains of the metal such that their "easy" axes of magnetization all point in the same direction, freezing a strong magnetic field into the material. On the other hand, materials with low magnetic anisotropy usually

neg: Dipole model of the Earth's magnetic field formula_1 as the mean value of the magnetic field at the magnetic equator on the Earth's surface. Typically formula_2. Then, the radial and azimuthal fields can be described as formula_3 formula_4 formula_5 where formula_6 is the mean radius of the Earth (approximately 6370 km), formula_7 is the radial distance from the center of the Earth (using the same units as used for formula_6), and formula_9 is the azimuth measured from the north magnetic pole (or geomagnetic pole). It is sometimes more convenient to express the magnetic field in terms of magnetic latitude and distance in Earth radii. The magnetic latitude

neg: Dynamo theory Dynamo theory In physics, the dynamo theory proposes a mechanism by which a celestial body such as Earth or a star generates a magnetic field. The dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales. A dynamo is thought to be the source of the Earth's magnetic field and the magnetic fields of other planets. When William Gilbert published "de Magnete" in 1600, he concluded that the Earth is magnetic and proposed the first hypothesis for the origin of this magnetism: permanent magnetism such as that

neg: Interplanetary magnetic field a shape similar to a twirled ballerina skirt, and changes in shape through the solar cycle as the Sun's magnetic field reverses about every 11 years. The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's magnetic dipole field, about 10 teslas at the surface of the Sun, would reduce with the inverse cube of the distance to about 10 teslas. But satellite observations show that it is about 100 times

neg: Atmospheric escape Earth is bound as O, which is too massive to escape Earth by Jeans escape. Earth's magnetic field protects it from solar winds and prevents escape of ions, except near the magnetic poles where charged particles stream towards the earth along magnetic field lines. The gravitational attraction of Earth's mass prevents other non-thermal loss processes from appreciably depleting the atmosphere. Yet Earth's atmosphere is two orders of magnitude less dense than that of Venus at the surface. Because of the temperature regime of Earth, CO and HO are sequestered in the hydrosphere and lithosphere. HO vapor is sequestered as liquid

neg: Earth's magnetic field the core (planetary differentiation, the iron catastrophe) as well as decay of radioactive elements in the interior. The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core. The mechanism by which the Earth generates a magnetic field is known as a dynamo. The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force). These

neg: L3 experiment stop most particles, measuring their energy. A set of scintillation counters was placed between the electro-magnetic and hadronic calorimeters: one of their functions was to help in recognising and rejecting signals coming from cosmic ray muons, very highly energetic particles which come from the space and can disturb the measurement. The outermost layer contained the magnet that generated, inside the detector, a magnetic field about 10000 times the average field on the surface of the Earth. This field deflected the charged particles which crossed it and the curvature of this deflection was a way of reconstructing the energy of the

neg: Super-Earth a lower black body temperature than the more absorbent (lower albedo) Earth. Earth's magnetic field results from its flowing liquid metallic core, but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles. Magnesium oxide, which is rocky on Earth, can be a liquid metal at the pressures and temperatures found in super-Earths and could generate a magnetic field in the mantles of super-Earths. That said, super-Earth magnetic fields are yet to be detected observationally. According to one

neg: Earth's magnetic field This process could go on generating new field indefinitely, were it not that as the magnetic field increases in strength, it resists fluid motion. The motion of the fluid is sustained by convection, motion driven by buoyancy. The temperature increases towards the center of the Earth, and the higher temperature of the fluid lower down makes it buoyant. This buoyancy is enhanced by chemical separation: As the core cools, some of the molten iron solidifies and is plated to the inner core. In the process, lighter elements are left behind in the fluid, making it lighter. This is called "compositional

neg: Earth–ionosphere waveguide is, that near the antipode the field strength slightly increases. Due to the influence of the Earth' magnetic field, the medium becomes anisotropic so that the ionospheric reflection factor in reality is a matrix. This means that a vertically polarized incident wave after reflection at the ionospheric D-layer converses to a vertically and a horizontally polarized wave. Moreover, the geomagnetic field gives rise to a nonreciprocity of VLF waves. Waves propagating from east to west are more strongly attenuated than vice versa. There appears a phase slipping near the distance of the deep interference minimum of eq. (3). During the

neg: Timeline of United States inventions (1890–1945) the magnetic field of the Earth. The operation of the compass is based on the principle of electromagnetic induction with the Earth's magnetic field acting as the induction field for an electric generator. A variation generated voltage, thus allows the Earth inductor compass to determine direction. The earth inductor compass is an American invention. It was designed in 1924 by Morris Titterington at the Pioneer Instrument Company. Designed to compensate for the weaknesses of the magnetic compass, the Earth inductor compass provided pilots with a more stable and reliable reference instrument. 1924 Gas chamber execution 1924 Moviola 1924 Radio altimeter

neg: Geomagnetic pole the direction of the magnetic field in previous times as one moves farther away to older ocean floor. Geomagnetic pole The geomagnetic poles are antipodal points where the axis of a best-fitting dipole intersects the surface of Earth. This theoretical dipole is equivalent to a powerful bar magnet at the center of Earth and comes closer than any other model to accounting for the magnetic field observed at Earth's surface. In contrast, the magnetic poles of the actual Earth are not antipodal; that is, the line on which they lie does not pass through Earth's center. Owing to motion of

neg: Metal it would have a height of nearly 700 light years. The magnetic field shields the Earth from the charged particles of the solar wind, and cosmic rays that would otherwise strip away the upper atmosphere (including the ozone layer that limits the transmission of ultraviolet radiation). Metals are often extracted from the Earth by means of mining ores that are rich sources of the requisite elements, such as bauxite. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and

neg: Magnetoreception magnetoreceptive basis for many species including turtles. Electromagnetic induction has not been observed nor tested in non-aquatic animals. Additionally, it remains likely that two or more complementary mechanisms play a role in magnetic field detection in animals. Of course, this potential dual mechanism theory raises the question, to what degree is each method responsible for the stimulus, and how do they produce a signal in response to the low magnetic field of the Earth? Then there is the distinction of magnetic usage. Some species may only be able to sense a magnetic compass to find north and south, while others

neg: Earth–ionosphere waveguide Earth and the ionosphere. The round-the-world nature of the waveguide produces resonances, like a cavity, which are at ~7 Hz. Radio propagation within the ionosphere depends on frequency, angle of incidence, time of day, season, Earth's magnetic field, and solar activity. At vertical incidence, waves with frequencies larger than the electron plasma frequency (f) of the F-layer maximum (1) f = 9 (N) kHz (N in cm is the electron density) can propagate through the ionosphere nearly undisturbed. Waves with frequencies smaller than f are reflected within the ionospheric D-, E-, and F-layers. f is of the order of 8–15

neg: Earth inductor compass Earth inductor compass The Earth inductor compass (or simply induction compass) is a compass that determines directions using the principle of electromagnetic induction, with the Earth's magnetic field acting as the induction field for an electric generator. The electrical output of the generator will vary depending on its orientation with respect to the Earth's magnetic field. This variation in the generated voltage is measured, allowing the Earth inductor compass to determine direction. The earth inductor compass was first patented by Donald M. Bliss in 1912 and further refined in the 1920s by Paul R. Heyl and Lyman James Briggs of

neg: Ionospheric dynamo region Ionospheric dynamo region In the height region between about 85 and 200 km altitude on Earth, the ionospheric plasma is electrically conducting. Atmospheric tidal winds due to differential solar heating or due to gravitational lunar forcing move the ionospheric plasma against the geomagnetic field lines thus generating electric fields and currents just like a dynamo coil moving against magnetic field lines. That region is therefore called ionospheric dynamo region. The magnetic manifestation of these electric currents on the ground can be observed during magnetospheric quiet conditions. They are called Sq-variations (S=solar; q=quiet) and L-variations (L=lunar) of the geomagnetic field. Additional

neg: Incremental dating layer or layers of sediment. Typically, varve refers to lake or glacial sediment), as temperature induced changes in the isotopic ratios for oxygen isotopes in sediments, and in the relative abundance of fossils. Because these can be calibrated reliably over a period of 40 million years this provides an alternate verification to radiometric dating in cases where sufficient record exists to provide a reliable trace. Polarity reversals in the Earth's magnetic field have also been used to determine geologic time. Periodically, the magnetic field of the earth reverses leaving a magnetic signal in volcanic and sedimentary rocks. This signal can

neg: Geomagnetically induced current Earth structure using magnetotellurics, but it also creates a hazard. This geomagnetic hazard is primarily a risk to technology under the Earth's protective atmospheric blanket. A time-varying magnetic field external to the Earth induces telluric currents—electric currents in the conducting ground. These currents create a secondary (internal) magnetic field. As a consequence of Faraday's law of induction, an electric field at the surface of the Earth is induced associated with time variations of the magnetic field. The surface electric field causes electrical currents, known as geomagnetically induced currents (GIC), to flow in any conducting structure, for example, a power or

neg: Interplanetary medium heliopause, and exhibits filamentation (such as in aurorae). The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's 10 tesla magnetic dipole field would reduce with the cube of the distance to about 10 tesla. But satellite observations show that it is about 100 times greater at around 10 tesla. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g., the interplanetary medium) in a magnetic field induces electric

neg: Geomagnetic storm were interrupted due to the storm. The solar wind also carries with it the Sun's magnetic field. This field will have either a North or South orientation. If the solar wind has energetic bursts, contracting and expanding the magnetosphere, or if the solar wind takes a southward polarization, geomagnetic storms can be expected. The southward field causes magnetic reconnection of the dayside magnetopause, rapidly injecting magnetic and particle energy into the Earth's magnetosphere. During a geomagnetic storm, the ionosphere's F layer becomes unstable, fragments, and may even disappear. In the northern and southern pole regions of the Earth, auroras are

neg: Earth–ionosphere waveguide wave which arrives directly at the receiver and multihop sky waves reflected at the ionospheric D-layer (Figure 1). For the real Earth's surface, the ground wave becomes dissipated and depends of the orography along the ray path. For VLF waves at shorter distances, this effect is, however, of minor importance, and the reflection factor of the Earth is R = 1, in a first approximation. At shorter distances, only the first hop sky wave is of importance. The D-layer can be simulated by a magnetic wall (R = -1) with a fixed boundary at a virtual height h, which means

neg: Magnetic nozzle pressure being confined by the magnetic field gives rise to a diamagnetic drift, which is proportional to the pressure of electrons and inversely proportional to the magnetic field strength. Together with the formula_1 drift, the diamagnetic drift is responsible of the formation of an "azimuthal electric current" formula_2 in the plasma domain. This azimuthal electric current generates an induced magnetic field which opposes the applied one, generating a repulsive magnetic force formula_3 that pushes the plasma downstream. The reaction to this force is felt on the magnetic generator of the magnetic nozzle and is called magnetic thrust. This is the

neg: Astronautical hygiene radiation belts. Space station crew exposures will be much higher than those on Earth and unshielded astronauts may experience serious health effects if unprotected. Galactic cosmic radiation is extremely penetrating and it may not be possible to build shields of sufficient depth to prevent or control exposure. The Earth's magnetic field is responsible for the formation of the trapped radiation belts that surround Earth. The ISS orbits at between and , known as a Low Earth Orbit (LEO). Trapped radiation doses in LEO decrease during solar maximum and increase during solar minimum. Highest exposures occur in the South Atlantic Anomaly

neg: Dynamo theory found in lodestone. In 1919, Joseph Larmor proposed that a dynamo might be generating the field. However, even after he advanced his hypothesis, some prominent scientists advanced alternative explanations. Einstein believed that there might be an asymmetry between the charges of the electron and proton so that the Earth's magnetic field would be produced by the entire Earth. The Nobel Prize winner Patrick Blackett did a series of experiments looking for a fundamental relation between angular momentum and magnetic moment, but found none. Walter M. Elsasser, considered a "father" of the presently accepted dynamo theory as an explanation of the

neg: Earth the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail. Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bowshock precedes the dayside magnetosphere within the solar wind. Charged particles are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates; the ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field, and

neg: Magnetic dip weighted during manufacture to compensate for magnetic dip, so that they will balance roughly horizontally. This balancing is latitude-dependent; see Compass balancing (magnetic dip). Magnetic dip Magnetic dip, dip angle, or magnetic inclination is the angle made with the horizontal by the Earth's magnetic field lines. This angle varies at different points on the Earth's surface. Positive values of inclination indicate that the magnetic field of the Earth is pointing downward, into the Earth, at the point of measurement, and negative values indicate that it is pointing upward. The dip angle is in principle the angle made by the needle

neg: Rare-earth magnet temperature at which the material loses its magnetism. Rare-earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types. The table below compares the magnetic performance of the two types of rare-earth magnets, neodymium (NdFeB) and samarium-cobalt (SmCo), with other types of permanent magnets. Source: Samarium–cobalt magnets (chemical formula: SmCo), the first family of rare-earth magnets invented, are less used than neodymium magnets because of their higher cost and lower magnetic field strength. However, samarium–cobalt has a higher Curie temperature, creating a niche for these magnets in applications where high field

neg: Rare-earth magnet high remanence (saturation magnetization "J"). The maximal energy density "BH" is proportional to "J", so these materials have the potential for storing large amounts of magnetic energy. The magnetic energy product "BH" of neodymium magnets is about 18 times greater than "ordinary" magnets by volume. This allows rare-earth magnets to be smaller than other magnets with the same field strength. Some important properties used to compare permanent magnets are: remanence ("B"), which measures the strength of the magnetic field; coercivity ("H"), the material's resistance to becoming demagnetized; energy product ("BH"), the density of magnetic energy; and Curie temperature ("T"), the

neg: Earth's magnetic field magnetic surveys. , the latest version, EMM2017, includes data from The European Space Agency's Swarm satellite mission. Animals including birds and turtles can detect the Earth's magnetic field, and use the field to navigate during migration. Some researchers have found that cows and wild deer tend to align their bodies north-south while relaxing, but not when the animals are under high-voltage power lines, suggesting that magnetism is responsible. Other researchers reported in 2011 that they could not replicate those findings using different Google Earth images. Researchers found out that very weak electromagnetic fields disrupt the magnetic compass used by European

neg: 38 Virginis b a geodynamo effect which would give the satellite a strong magnetic field. To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 . One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that Jupiter's moon Ganymede has its own magnetosphere, even though its mass is only 0.025 . The search for

neg: Rare-earth magnet compounds have Curie temperatures well above room temperature. Rare-earth magnets are made from these compounds. The greater strength of rare-earth magnets is mostly due to two factors. First, their crystalline structures have very high magnetic anisotropy. This means that a crystal of the material preferentially magnetizes along a specific crystal axis but is very difficult to magnetize in other directions. Like other magnets, rare-earth magnets are composed of microcrystalline grains, which are aligned in a powerful magnetic field during manufacture, so their magnetic axes all point in the same direction. The resistance of the crystal lattice to turning its direction

neg: HD 69830 d moon to sustain plate tectonics, which would cause volcanic activity to regulate the moon's temperature and create a geodynamo effect which would give the satellite a strong magnetic field. To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 . One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that Jupiter's

neg: Crustal magnetism Crustal magnetism Crustal magnetism is the magnetic field of the crust of a planetary body. The crustal magnetism of Earth has been studied, in particular various magnetic crustal anomalies have been studied. Two examples of crustal magnetic anomalies on Earth that been studied the Americas are the Brunswick magnetic anomaly (BMA) and East Coast magnetic anomaly (ECMA). Also there can be a correlation between physical geological features and certain readings from crustal magnetism on Earth. Below the surface of the Earth the temperature increases and so the crustal magnetism is lost because it rises above the curie temperate of the

neg: Diver navigation which remains pointing in the same direction (Magnetic North) all the time. There are occasions when the card does turn, but this is when it has been stuck or the compass is turned over, and the card is unable to remain aligned with the magnetic field. True north is the geometrically accurate direction along the surface of the earth toward the North pole of the planet’s axis of rotation. The lines of longitude on maps are in true North/South directions. The Earth has a magnetic field which is not quite in line with the geographic directions. The difference between the

neg: BD+14 4559 b the moon's temperature and create a geodynamo effect which would give the satellite a strong magnetic field. To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 . One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that Jupiter's moon Ganymede has its own magnetosphere, even though its mass is only

neg: Bow shocks in astrophysics speed between the plasma and the object. Magnetic draping has been detected around planets, moons, solar coronal mass ejections, and galaxies. Bow shocks in astrophysics Bow shocks form the boundary between a magnetosphere and an ambient (or at least surrounding) magnetized medium. This occurs when the magnetic field of an astrophysical object interacts with the nearby flowing ambient plasma. For example, when the solar wind, flowing with a relative speed of order 400 km/s, encounters the magnetic field of Earth, a bow shape boundary forms. For Earth and other magnetized planets, it is the boundary at which the speed of

neg: Magnetar of times stronger than any man-made magnet, and quadrillions of times more powerful than the field surrounding Earth. Earth has a geomagnetic field of 30–60 microteslas, and a neodymium-based, rare-earth magnet has a field of about 1.25 tesla, with a magnetic energy density of 4.0×10 J/m. A magnetar's 10 tesla field, by contrast, has an energy density of 4.0×10 J/m, with an "E/c" mass density more than 10,000 times that of lead. The magnetic field of a magnetar would be lethal even at a distance of 1000 km due to the strong magnetic field distorting the electron clouds of the

neg: Mutation breeding this program is unfeasible outside of China. Due to such restraints, scientists have been trying to replicate space condition on Earth in order to promote the same expedient space-born mutations on Earth. One such replication is a magnetic field-free space (MF), which produces an area with a weaker magnetic field than that of Earth. MF treatment produced mutagenic results, and has been used to cultivate new mutant varieties of rice and alfalfa. Other replications of space conditions include irradiation of seeds by a heavy 7 Li-ion beam or mixed high-energy particles. These space-bred varieties are already being introduced to the

neg: Roy Henry Garstang of highly ionized species of iron, and spent time studying the effects of strong magnetic field on atomic spectra, ranging from the thousand gauss fields of sunspots to megagauss fields of white dwarfs. Later in his career, Garstang began to work on light pollution. Between 1984 and 2007, he published 40 scientific papers concerning the phenomenon, and constructed a light pollution model which included an ozone layer, scattering of light by molecules and aerosols with improved variations with altitude, curvature of the earth, and a dust layer of dust either volcanic or desert origin. The models he created have since

neg: Skip distance some are absorbed, some refracted while a portion escapes to the next layer. At this higher layer, there is a possibility of this radio wave being bent downwards to earth again. This bending happens because each layer of the ionosphere has a refractive index that varies from that of the others. Because of the differing heights of refraction, or apparent reflection, the radio waves hit the earth surface at different points hence generating the skip distance. Skip distance is greatest during the night when the ionosphere is the highest. Maximum usable frequency Skip distance A skip distance is the distance

neg: South Atlantic Anomaly South Atlantic Anomaly The South Atlantic Anomaly (SAA) is an area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface, dipping down to an altitude of . This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher-than-usual levels of radiation. The effect is caused by the non-concentricity of the Earth and its magnetic dipole. The SAA is the near-Earth region where the Earth's magnetic field is weakest relative to an idealized Earth-centered dipole field. The area of the SAA is confined by the intensity of Earth's magnetic

neg: Kepler-90h same to have a stable orbit. Tidal effects could also allow the moon to sustain plate tectonics, which would cause volcanic activity to regulate the moon's temperature and create a geodynamo effect which would give the satellite a strong magnetic field. To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 . One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's

neg: Magnetic dip Magnetic dip Magnetic dip, dip angle, or magnetic inclination is the angle made with the horizontal by the Earth's magnetic field lines. This angle varies at different points on the Earth's surface. Positive values of inclination indicate that the magnetic field of the Earth is pointing downward, into the Earth, at the point of measurement, and negative values indicate that it is pointing upward. The dip angle is in principle the angle made by the needle of a vertically held compass, though in practice ordinary compass needles may be weighted against dip or may be unable to move freely in

neg: Magnetic field of the Moon Magnetic field of the Moon The magnetic field of the Moon is very weak in comparison to that of the Earth. Other major differences are that the Moon does not currently have a dipolar magnetic field (as would be generated by a geodynamo in its core) and the varying magnetization that is present is almost entirely crustal in origin. One hypothesis holds that the crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. An analysis of magnetized moon rocks brought to Earth by Apollo astronauts showed that the moon must have had a strong (above

neg: Mercury (planet) likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth. This dynamo effect would result from the circulation of the planet's iron-rich liquid core. Particularly strong tidal effects caused by the planet's high orbital eccentricity would serve to keep the core in the liquid state necessary for this dynamo effect. Mercury's magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, though small enough to fit within Earth, is strong enough to trap solar wind plasma. This contributes to the

neg: Extremely low frequency long distances without escaping into space. In contrast to VLF waves, the height of the layer is much less than one wavelength at ELF frequencies, so the only mode that can propagate at ELF frequencies is the TEM mode in vertical polarization, with the electric field vertical and the magnetic field horizontal. ELF waves have extremely low attenuation of 1–2 dB per 1000 km, giving a single transmitter the potential to communicate worldwide. ELF waves can also travel considerable distances through "lossy" media like earth and seawater, which would absorb or reflect higher frequency radio waves. The attenuation of ELF

neg: Crustal magnetism been examined on Earth and on Mars. However, these are the only bodies that have by the early 21st century they have been studied even though it is predicted other bodies will have this geological feature. Crustal magnetism Crustal magnetism is the magnetic field of the crust of a planetary body. The crustal magnetism of Earth has been studied, in particular various magnetic crustal anomalies have been studied. Two examples of crustal magnetic anomalies on Earth that been studied the Americas are the Brunswick magnetic anomaly (BMA) and East Coast magnetic anomaly (ECMA). Also there can be a correlation between

neg: Bonded neo later be shaped by injection moulding. An external magnetic field is applied during the moulding process, orienting the field of the completed magnet. Bonded neo Bonded neo powder is produced by processing specific combination of elements that result in distinct magnetic and physical characteristics. These powders are the primary material used in the manufacture of bonded rare earth permanent magnets, which, in turn, are used in motors and sensors utilized in a wide variety of products for consumer and industrial end markets. Neodymium metal, one of the rare earth elements, is the primary raw material in neo powder. It is

neg: Atmospheric escape loss of atmosphere. On Earth, for instance, the interaction between the solar wind and earth's magnetic field deflects the solar wind around the planet, with near total deflection at a distance of 10 Earth radii. This region of deflection is called a bow shock. Depending on planet size and atmospheric composition, however, a lack of magnetic field does not fully determine the fate of a planet's atmosphere. Venus, for instance, has no powerful magnetic field. Its close proximity to the Sun also increases the speed and number of particles, and would presumably cause the atmosphere to be stripped almost entirely,

neg: Mercury's magnetic field around 300 nT, which is weaker than that of Jupiter's moon Ganymede. Mercury's magnetic field is weaker than Earth's because its core had cooled and solidified more quickly than Earth's. Although Mercury's magnetic field is much weaker than Earth's magnetic field, it is still strong enough to deflect the solar wind, inducing a magnetosphere. Because Mercury's magnetic field is weak while the interplanetary magnetic field it interacts with in its orbit is relatively strong, the solar wind dynamic pressure at Mercury′s orbit is also three times larger than at Earth. Whether the magnetic field changed to any significant degree between

neg: Thomas Gold prediction of a collisionless shock wave, arguing that solar flares would eject material into magnetic clouds to produce a shock front that would result in geomagnetic storms. He also coined the term "magnetosphere" in his paper "Motions in the Magnetosphere of the Earth" to describe "the region above the ionosphere in which the magnetic field of the Earth has a dominant control over the motions of gas and fast charged particles ... [which was] known to extend out to a distance of the order of 10 Earth radii". In 1960, Gold collaborated again with Fred Hoyle to show that magnetic

neg: Rare-earth magnet of magnetization gives these compounds a very high magnetic coercivity (resistance to being demagnetized). Second, atoms of rare-earth elements can have high magnetic moments because their orbital electron structure contains many unpaired electrons, in contrast to other elements, in which almost all of the electrons exist in pairs with opposite spins, so their magnetic fields cancel out. This is a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired electrons. In a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field. This gives the materials

neg: L-shell mapping the real, non-dipolar terrestrial or planetary field into coordinates that behave essentially like those of a perfect dipole. The "L" parameter is traditionally labeled in Earth-radii, of the point where the shell crosses the magnetic Equator, of the equivalent dipole. "B" is measured in gauss. In a centered dipole magnetic field model, the path along a given L shell can be described as formula_2 where formula_3 is the radial distance (in earth radii) to a point on the line, formula_4 is its geomagnetic latitude, and formula_5 is the L-shell of interest. For the Earth, L-shells uniquely define regions of

neg: Earth's magnetic field 60 km, extends up to 3 or 4 Earth radii, and includes the ionosphere. This region rotates with the Earth. There are also two concentric tire-shaped regions, called the Van Allen radiation belts, with high-energy ions (energies from 0.1 to 10 million electron volts (MeV)). The inner belt is 1–2 Earth radii out while the outer belt is at 4–7 Earth radii. The plasmasphere and Van Allen belts have partial overlap, with the extent of overlap varying greatly with solar activity. As well as deflecting the solar wind, the Earth's magnetic field deflects cosmic rays, high-energy charged particles that are

neg: L-shell model. Although L-value is formally defined in terms of the Earth's true instantaneous magnetic field (or a high-order model like IGRF), it is often used to give a general picture of magnetic phenomena near the Earth, in which case it can be approximated using the dipole model of the Earth's magnetic field. The motions of low-energy charged particles in the Earth's magnetic field (or in any nearly-dipolar magnetic field) can be usefully described in terms of McIlwain's "(B,L)" coordinates, the first of which, "B" is just the magnitude (or length) of the magnetic field vector. This description is most valuable

neg: Ken Ring (writer) far left" and "full of bad science". During the launch of his 2008 almanac he said that "we have a responsibility to create global warming" as "life likes warmth". Ring predicts earthquakes based on the position of the moon. On his website he says that when the moon (in particular the new moon) is at perigee (closest to the earth) it may affect the Earth's mantle and alter the magnetic field. It may also draw the Van Allen Belt closer, attracting radioactively charged particles towards Earth. Ring believes this combination may be responsible for earthquakes and volcanoes. Ring has predicted

neg: Bow shocks in astrophysics Bow shocks in astrophysics Bow shocks form the boundary between a magnetosphere and an ambient (or at least surrounding) magnetized medium. This occurs when the magnetic field of an astrophysical object interacts with the nearby flowing ambient plasma. For example, when the solar wind, flowing with a relative speed of order 400 km/s, encounters the magnetic field of Earth, a bow shape boundary forms. For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause. For stars, this boundary is typically the

neg: Solar wind gently than, CMEs. Over the Sun's lifetime, the interaction of its surface layers with the escaping solar wind has significantly decreased its surface rotation rate. The wind is considered responsible for comets' tails, along with the Sun's radiation. The solar wind contributes to fluctuations in celestial radio waves observed on the Earth, through an effect called interplanetary scintillation. Where the solar wind intersects with a planet that has a well-developed magnetic field (such as Earth, Jupiter or Saturn), the particles are deflected by the Lorentz force. This region, known as the magnetosphere, causes the particles to travel around the planet

neg: Space exploration their discovery by the United States' first artificial satellite, "Explorer 1". These belts contain radiation trapped by Earth's magnetic fields, which currently renders construction of habitable space stations above 1000 km impractical. Following this early unexpected discovery, a large number of Earth observation satellites have been deployed specifically to explore Earth from a space based perspective. These satellites have significantly contributed to the understanding of a variety of Earth-based phenomena. For instance, the hole in the ozone layer was found by an artificial satellite that was exploring Earth's atmosphere, and satellites have allowed for the discovery of archeological sites or

neg: Very low frequency the bottom of the ionosphere called the D layer at 60 to 90 km (37 to 56 miles) altitude, which reflects VLF radio waves. The conductive ionosphere and the conductive Earth form a horizontal "duct" a few VLF wavelengths high, which acts as a waveguide confining the waves so they don't escape into space. The waves travel in a zigzag path around the Earth, reflected alternately by the Earth and the ionosphere, in TM (transverse magnetic) mode. VLF waves have very low path attenuation, 2-3 dB per 1000 km, with little of the "fading" experienced at higher frequencies, This is

neg: Canadian Geospace Monitoring going on further out in near-Earth space. In this way, observations of the ionospheric processes can be used to in turn remote sense dynamics in near-Earth space. The interaction is significant at sub-auroral, auroral, and polar latitudes where large regions of the magnetosphere are mapped along the magnetic field into relatively small regions of the ionosphere, and where the magnetospheric dynamics are controlled primarily by the plasma rather than the magnetic field. This organization is actually by magnetic rather than by geographic latitude (see Baker and Wing, and references therein for a description of magnetic vs. geographic coordinates). The aurora,

neg: Background radiation hours per year in this environment. During their flights airline crews typically get an additional occupational dose between per year and 2.19 mSv/year, according to various studies. Similarly, cosmic rays cause higher background exposure in astronauts than in humans on the surface of Earth. Astronauts in low orbits, such as in the International Space Station or the Space Shuttle, are partially shielded by the magnetic field of the Earth, but also suffer from the Van Allen radiation belt which accumulates cosmic rays and results from the Earth's magnetic field. Outside low Earth orbit, as experienced by the Apollo astronauts who

neg: Magsat magnetometer for determining the magnetic field caused by the vector magnetometer itself. MAGSAT is considered to be one of the more important Science/Earth orbiting satellites launched; the data it accumulated is still being used, particularly in linking new satellite data to past observations. After launch the payload was brought to an orbit of 96.8° facing the Sun as the Earth rotated underneath. It was kept in a close Earth orbit, with vector magnetometers capable of sensing magnetic fields closer to Earth's surface. The data collected by this satellite allowed a 3D-mapping of the Earth's magnetic interior as never seen before.

neg: Spacecraft propulsion large collection surface to function effectively. The magnetic sail deflects charged particles from the solar wind with a magnetic field, thereby imparting momentum to the spacecraft. A variant is the mini-magnetospheric plasma propulsion system, which uses a small cloud of plasma held in a magnetic field to deflect the Sun's charged particles. An E-sail would use very thin and lightweight wires holding an electric charge to deflect these particles, and may have more controllable directionality. As a proof of concept, NanoSail-D became the first nanosatellite to orbit Earth. There are plans to add them to future Earth orbit satellites, enabling

neg: Uranus as high as 1.1 gauss (110 µT). The average field at the surface is 0.23 gauss (23 µT). Studies of "Voyager 2" data in 2017 suggest that this asymmetry causes Uranus's magnetosphere to connect with the solar wind once a Uranian day, opening the planet to the Sun's particles. In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator. The dipole moment of Uranus is 50 times that of Earth. Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a

neg: Astrophysical X-ray source of 10 million amps – a hundred times greater than the most powerful lightning bolts – are required to explain the auroras at Jupiter's poles, which are a thousand times more powerful than those on Earth. On Earth, auroras are triggered by solar storms of energetic particles, which disturb Earth's magnetic field. As shown by the swept-back appearance in the illustration, gusts of particles from the Sun also distort Jupiter's magnetic field, and on occasion produce auroras. Saturn's X-ray spectrum is similar to that of X-rays from the Sun indicating that Saturn's X-radiation is due to the reflection of solar

neg: Dipole model of the Earth's magnetic field (MLAT), or geomagnetic latitude, formula_10 is measured northwards from the equator (analogous to geographic latitude) and is related to formula_9 by formula_12. In this case, the radial and azimuthal components of the magnetic field (the latter still in the formula_9 direction, measured from the axis of the north pole) are given by formula_14 formula_15 formula_16 where formula_17 in this case has units of Earth radii (formula_18). Invariant latitude is a parameter that describes where a particular magnetic field line touches the surface of the Earth. It is given by formula_19 or formula_20 where formula_21 is the invariant latitude and formula_22

neg: Astrionics ways in which ACS can obtain the necessary measurements to determine this. This device measures the strength of the Earth's magnetic field in one direction. For measurements on all three axes, the device would consist of three orthogonal magnetometers. Given the spacecraft's position, the magnetic field measurements can be compared to a known magnetic field which is given by the International Geomagnetic Reference Field model. Measurements made by magnetometers are affected by noise consisting of alignment error, scale factor errors, and spacecraft electrical activity. For near Earth orbits, the error in the modeled field direction may vary from 0.5 degrees

neg: Solar wind suggests that Kelvin-Helmholtz waves can be a somewhat common, and possibly constant, instrument for the entrance of solar wind into terrestrial magnetospheres under various IMF orientations. The solar wind affects other incoming cosmic rays interacting with planetary atmospheres. Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind. Venus, the nearest and most similar planet to Earth, has 100 times denser atmosphere, with little or no geo-magnetic field. Space probes discovered a comet-like tail that extends to Earth's orbit. Earth itself is largely protected from the solar wind by its magnetic field, which

neg: Planetary science its interaction with the solar wind forms a magnetosphere around a planet. Early space probes discovered the gross dimensions of the terrestrial magnetic field, which extends about 10 Earth radii towards the Sun. The solar wind, a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail, hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles, the Van Allen radiation belts. Geophysics includes seismology and tectonophysics, geophysical fluid dynamics, mineral physics, geodynamics, mathematical geophysics, and geophysical surveying. Planetary geodesy, (also known as planetary geodetics)

neg: Martin A. Pomerantz cosmic rays from sites at varying latitudes around the Earth. Several of these expeditions were sponsored by the National Geographic Society. He supervised the installation of a stationary cosmic ray detector facility at Thule Air Base in Greenland, and in 1960 Pomerantz installed a cosmic ray detector at McMurdo Station in Antarctica. Pomerantz' experiments at the South Pole commenced in 1964. These experiments and expeditions led to several insights, one of which was an inference about the magnetic field of the sun. Like the Earth, the sun has a magnetic field. Initial estimates suggested that the sun's magnetic strength was

neg: Earth's magnetic field convection". A Coriolis effect, caused by the overall planetary rotation, tends to organize the flow into rolls aligned along the north-south polar axis. A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a T-Tauri phase in which the solar wind would have had a magnetic field orders of magnitude larger than the present solar wind. However, much of the field may have been screened out by the Earth's mantle. An alternative source is

neg: Dipole model of the Earth's magnetic field is the L-shell describing the magnetic field line in question. On the surface of the earth, the invariant latitude (formula_21) is equal to the magnetic latitude (formula_10). Dipole model of the Earth's magnetic field The dipole model of the Earth's magnetic field is a first order approximation of the rather complex true Earth's magnetic field. Due to effects of the interplanetary magnetic field (IMF), and the solar wind, the dipole model is particularly inaccurate at high L-shells (e.g., above L=3), but may be a good approximation for lower L-shells. For more precise work, or for any work at higher L-shells,

neg: Rare-earth magnet Rare-earth magnet Rare-earth magnets are strong permanent magnets made from alloys of rare-earth elements. Developed in the 1970s and 1980s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium–cobalt magnets. Magnetostrictive rare-earth magnets such as Terfenol-D also have applications, e.g. in loudspeakers. Rare-earth magnets are extremely brittle and also vulnerable to corrosion,

neg: Isolated-phase bus housing, in the opposite direction from the phase current. The magnetic field produced by this current nearly exactly cancels the magnetic field produced by the phase current, so there is almost no external magnetic field produced. This also limits the amount of force produced between conductors during a short circuit. The external housings of the conductors remain at a low potential with respect to earth ground and are usually bonded to ground. By enclosing the conductors in separate housings a high degree of protection from two-phase and three-phase faults is obtained. Almost any fault would instead be a single-phase earth

neg: A Beautiful Planet as "The Great Dying"). Like the force fields which protect fictional spaceships from damage, Spaceship Earth has a very real magnetic field which prevents cosmic rays and the stream of charged particles emitted by the Sun from harming living beings on Earth. In the narrative words of "A Beautiful Planet", the glowing, curtain-like auroras that the astronauts admire in the film "show that shield in action. Because we have this magical magnetic field protecting us, we have our forests, and oceans, animals, and people. It's why ours is a planet of life." Our neighboring planet Mars, on the other hand,

neg: Earth's magnetic field zero or more latitude circles; this plus the order is equal to the "degree" ℓ. Each harmonic is equivalent to a particular arrangement of magnetic charges at the center of the Earth. A "monopole" is an isolated magnetic charge, which has never been observed. A "dipole" is equivalent to two opposing charges brought close together and a "quadrupole" to two dipoles brought together. A quadrupole field is shown in the lower figure on the right. Spherical harmonics can represent any scalar field (function of position) that satisfies certain properties. A magnetic field is a vector field, but if it is

neg: Magnetic cloud of 0.15 AU with a typical speed of and magnetic field strength of 20 nT. Magnetic clouds represent about one third of ejecta observed by satellites at Earth. Other types of ejecta are multiple-magnetic cloud events (a single structure with multiple subclouds distinguishable) and complex ejecta, which can be the result of the interaction of multiple CMEs. Magnetic cloud A magnetic cloud is a transient event observed in the solar wind. It was defined in 1981 by Burlaga et al. 1981 as a region of enhanced magnetic field strength, smooth rotation of the magnetic field vector, and low proton temperature.

neg: Phaethontis quadrangle magnetic pole of one pointing up from the surface and the north magnetic pole of the next pointing down. When similar stripes were discovered on Earth in the 1960s, they were taken as evidence of plate tectonics. Researchers believe these magnetic stripes on Mars are evidence for a short, early period of plate tectonic activity. When the rocks became solid they retained the magnetism that existed at the time. A magnetic field of a planet is believed to be caused by fluid motions under the surface. However, there are some differences, between the magnetic stripes on Earth and those on

neg: Planetary core Niobium/tantalum (Nb/Ta) isotopic ratios, when compared with a chondritic reference frame, show mild depletion in bulk silicate Earth and the moon. Pallasites are thought to form at the core-mantle boundary of an early planetesimal, although a recent hypothesis suggests that they are impact-generated mixtures of core and mantle materials. Dynamo theory is a proposed mechanism to explain how celestial bodies like the Earth generate magnetic fields. The presence or lack of a magnetic field can help constrain the dynamics of a planetary core. Refer to Earth's magnetic field for further details. A dynamo requires a source of thermal and/or compositional

neg: Earth's magnetic field Changes over time scales of a year or more mostly reflect changes in the Earth's interior, particularly the iron-rich core. Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the K-index. Data from THEMIS show that the magnetic field, which interacts with the solar wind, is reduced when the magnetic orientation is aligned between Sun and Earth – opposite to the previous hypothesis. During forthcoming solar storms, this could result in blackouts and disruptions in artificial satellites. Changes in Earth's magnetic field on

neg: Swarm (spacecraft) Swarm (spacecraft) Swarm is a European Space Agency (ESA) mission to study the Earth's magnetic field. High-precision and high-resolution measurements of the strength, direction and variations of the Earth's magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide data for modelling the geomagnetic field and its interaction with other physical aspects of the Earth system. The results offer a view of the inside of the Earth from space, enabling the composition and processes of the interior to be studied in detail and increase our knowledge of atmospheric processes and ocean circulation patterns that affect climate and

neg: Electrodynamic tether and ions gyrate around magnetic field lines as they travel between the poles around the Earth due to magnetic mirroring forces and gradient-curvature drift. They gyrate at a particular radius and frequency dependence upon their mass, the magnetic field strength, and energy. These factors must be considered in current collection models. When the conducting body is negatively biased with respect to the plasma and traveling above the ion thermal velocity, there are additional collection mechanisms at work. For typical Low Earth Orbits (LEOs), between 200 km and 2000 km, the velocities in an inertial reference frame range from 7.8 km/s

neg: Dynamo theory developed by two groups in 1995, one in Japan and one in the United States. The latter received significant attention because it successfully reproduced some of the characteristics of the Earth's field, including geomagnetic reversals. Dynamo theory In physics, the dynamo theory proposes a mechanism by which a celestial body such as Earth or a star generates a magnetic field. The dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales. A dynamo is thought to be the source of the Earth's magnetic field and the magnetic