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W. R. Paterson - One of the best experts on this subject based on the ideXlab platform.
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plasmas observed near local noon in jupiter s magnetosphere with the Galileo Spacecraft
Journal of Geophysical Research, 2004Co-Authors: L. A. Frank, W. R. PatersonAbstract:[1] Measurements of electron beams and thermal ions were achieved by the Galileo Spacecraft during the later phases of its mission for three outbound passages of the local afternoon and noon sectors of Jupiter's magnetosphere. During the first two passages the Spacecraft passed through the rigidly corotating plasma torus with outer boundary near 8 RJ, into the transition region from torus to plasma sheet, and then into the plasma sheet proper at distances beyond ∼25 RJ. Telemetry coverage for the third passage began in the transition region. At the outer boundary of the torus the ion densities and temperatures were ∼500 cm−3 and 106 K. In the transition region the ion densities decreased with increasing distance to 0.1 cm−3, and temperatures increased to 5 × 107 K. In the plasma sheet the ion densities were typically 0.1 cm−3 with temperatures of 108 K. The azimuthal component of plasma flow slows to ∼70% of the corotational value in the transition region. For the first two passages, strong radial flows toward Jupiter increase with increasing radial distances. For the third passage near local noon the plasma flows are considerably more stagnant than those at local evening. The variations in the flow suggest that the solar wind influence extends to radial distances in the range of 10 RJ. Electron beams parallel and antiparallel to the magnetic field were observed during the passages on field lines connected to the main auroral ring in the ionosphere. Major constraints on the heating/acceleration mechanism for the main ring are (1) the presence of the electron beams at and near the equator and (2) previous remote observations of emissions in the vicinity of the atmospheric methane layer. These constraints support a heating mechanism in this layer driven by magnetospheric convection without acceleration by field-aligned electrostatic fields. At radial distances 30–44 RJ near local noon the plasma densities exhibited a System III effect, increasing once per planetary rotation near a longitude 300°. In addition, the finding of thermal ion beams directed parallel to the magnetic field near 20 RJ resolves the problem of radial force balance previously identified with Voyager measurements. That is, the outward centrifugal force for these beams is sufficient to balance the inward radial force of the magnetic field.
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plasmas observed with the Galileo Spacecraft during its flyby over io s northern polar region
Journal of Geophysical Research, 2002Co-Authors: L. A. Frank, W. R. PatersonAbstract:[1] On 8 August 2001 the tape recorder on board the Galileo Spacecraft provided high-resolution measurements of plasmas during a 1-hour interval centered on the closest approach to Io at an altitude of 200 km. During this period the Spacecraft trajectory was positioned at a radial distance from Jupiter of 5.9 RJ (Jupiter radii) and approached Io from upstream in the torus plasma flow, then over the northern polar region of Io, and subsequently into the downstream wake in the torus. The upstream and downstream ion densities as calculated from the moments of the measured three-dimensional velocity distributions were about 1200/cm3. These plasmas were rigidly corotating with Jupiter at 57 km/s. The upstream ions were characterized by the sum of four Maxwellian distributions, and the downstream distributions exhibited a similar set of thermal distributions with half the density of that found upstream and the remainder as pickup heavy ions freshly injected by the interaction of the torus flow with Io's ionosphere/atmosphere. The boundary of the Hill (Lagrange) sphere for Io's neutral gases which were co-orbiting with this moon was about 5 RIo (Io radii) from its center as identified by the onset of decreasing number densities and bulk flow speed as the Spacecraft approached Io. Closer to Io, and just before its entry and departure from magnetic field lines intercepting its northern polar surface, the diversion of incoming torus plasma by Io's face toward this flow and the subsequent downstream flow around Io were observed. Over Io's polar cap the torus plasma density was reduced by a factor of about 5 relative to that measured upstream and downstream from the Io interaction. The bulk flow speeds of the torus plasma were reduced to several km/s, an effect that is expected for the slow transport of magnetic flux in Io's conducting interior. A unique set of conditions allowed the detection of a cooler ion species with extremely high values of mass/charge in the range of 500 to 1000 amu. These ions are interpreted as clusters of SO2 molecules, or SO2 “snowflakes,” which briefly exist from the fresh injection and subsequent cooling of volcanic gases.
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passage through lo s ionospheric plasmas by the Galileo Spacecraft
Journal of Geophysical Research, 2001Co-Authors: L. A. Frank, W. R. PatersonAbstract:On February 22, 2000, the Galileo Spacecraft passed by the moon Io at a closest approach distance of 206 km. This altitude was sufficiently low that the plasma analyzer observed the three-dimensional ion velocity distributions as functions of energy/charge (E/Q) at the top of Io's ionosphere. The ionospheric ion distributions consisted of two populations, a warm distribution with density and temperature of ∼8000 cm -3 and 10,000 K and a cool population with 3000 cm -3 and 2300 K. This cooler temperature is in the range of those observed remotely for some volcanic plumes. The bulk speed of these ions was 2 km s -1 with respect to Io's surface. In order to identify the mass/unit charge (M/Q) of the ionospheric ions, the E/Q spectra of the pickup ions in this region were examined. The most probable M/Q of the primary population of these ions was inferred to be 64. Remote spectroscopic observations of Io's surface and atmosphere suggest that these ions are S 2 + and/or SO 2 + , although SO + and SO 3 + are not eliminated as possibilities. There is some evidence for lesser densities of heavier ions such as S 3 + and S 4 + . The densities, temperatures, and bulk flow velocities of torus ions were measured as the Spacecraft approached Io from the upstream direction. A combination of fits to the E/Q spectra observed with Galileo, the determinations of the M/Q of the primary ions with the plasma instrumentation on this Spacecraft during other passages, and the previous identification of the primary ions with Voyager 1 plasma and remote observations find the following primary composition for the unperturbed torus near Io: O ++ (50 cm -3 , 30 eV), O + (200 cm -3 , 30 eV), S ++ (400 cm -3 , 90 eV), and S + (100 cm -3 , 90 eV). At a radial distance from Io of ∼19,700 km (10.9 Io radii), changes in the torus ion density, temperature, and bulk flow velocity provide evidence that a cloud of neutral gases is co-orbiting with Io and is providing a substantial interaction with the torus ions.
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survey of thermal ions in the io plasma torus with the Galileo Spacecraft
Journal of Geophysical Research, 2001Co-Authors: L. A. Frank, W. R. PatersonAbstract:The densities, temperatures, and bulk flow velocities are reported for a series of six passages of the Galileo Spacecraft through Io's torus in Jupiter's magnetosphere. These observations were gained with the plasma analyzers on December 7, 1995, and July 1–2, August 12, September 14, October 11, and November 25, all of the latter in 1999. These plasma analyzers provided high-resolution measurements of the energy/charge (E/Q) spectra of the three-dimensional velocity distributions of the thermal ions that included determinations of the mass/charge (M/Q) of the primary ions with a mass spectrometer. The four dominant ions in the hot torus were two populations of ions with M/Q = 16 and two smaller populations with M/Q = 8 and 32, respectively. The identification of these four ions was based upon a best fit to the E/Q spectra of the measured three-dimensional ion velocity distributions. The two distributions with M/Q =16 were characterized by two different temperatures, in the ranges of 20 to 30 eV and 60 to 80 eV, respectively. On the basis of expectations of higher temperatures with higher masses for the pickup ions the cooler population is identified as O+, and the hotter as S++. The two smaller populations with M/Q = 8 and 32 are identified as O++ and S+, respectively. The temperatures were ∼20 eV for the O++ and 60 to 80 eV for the S+. The densities and temperatures of the ions in the hot torus remained constant during the period July through November 1999. However, the ion densities during the initial passage on December 7, 1995, were greater by factors of ∼3, which support the presence of long-term density variations of the torus plasmas but with relatively small fluctuations in the temperatures. A complete survey of System III longitudes was acquired with the set of six passages. The presence of an “active sector” at longitudes in the approximate range of 180° to 230° as originally found with remote observations of the torus brightnesses is confirmed with these Galileo measurements. In addition, further evidence for the importance of interchange motions for radial plasma transport was also evident in several of the Galileo passages, a dynamical process which was first identified in fields and particles measurements during the first passage through the torus on December 7, 1995. A persistent lag with an average in the range of ∼2 to 4 km/s in the azimuthal flows relative to that for rigid corotation was detected and supports the previously proposed System IV coordinate system that has a slightly slower rotation rate relative to that for System III.
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return to io by the Galileo Spacecraft plasma observations
Journal of Geophysical Research, 2000Co-Authors: L. A. Frank, W. R. PatersonAbstract:On October 11, 1999, a series of high-resolution plasma measurements were obtained during the second close flyby of Io of the Galileo mission. The closest approach to Io occurred at an altitude of 617 km along the flank of Jupiter's torus plasma flows past this moon. Energy/charge (E/Q) and mass/charge (M/Q) measurements with the plasma analyzer were used to identify the primary ions. At closest approach the ion number densities increased to their maximum values of 1200 cm -3 as calculated from the plasma moments. These ions were dominated by two thermal populations of torus ions with M/Q = 16, one with density and temperature of 800 cm -3 and kT= 40 eV and the other with 200 cm -3 and 160 eV. On the basis of the previous Voyager 1 remote measurements with a spectrometer, these two thermal ion plasmas are identified as O + and S ++ , respectively. A substantial population of pickup ions was also observed, with densities of about 100 cm -3 each for S + and SO + . The plasma bulk flows were strongly deflected around the body of Io, and the speed of the bulk flow increased to a factor of 1.3 greater than that for rigid corotational flow. The torus ion densities just outside of Io's orbit were about 800 cm -3 , These densities at the immediate position of Io are smaller by a factor of about 4 relative to those during the first flyby on December 7, 1995, but should not be taken as indicative of a similar decrease in the bulk of the plasma torus. Two major plasma regimes were encountered before the closest approach to Io. The first was a region of hot ions located inside of Io's orbit which was previously identified as the ribbon of enhanced plasma densities with Voyager 1 plasma measurements and with ground-based imagery. The ion composition in the ribbon included O + and S ++ . The second region, closer to Io, exhibited a hot torus plasma which was mixed with pickup hydrogen ions. These hydrogen ions were detected at distances beginning at 7.8 RIo from this moon, which were generally inside the Hill (Lagrange) sphere for Io's atmosphere.
L. A. Frank - One of the best experts on this subject based on the ideXlab platform.
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plasmas observed near local noon in jupiter s magnetosphere with the Galileo Spacecraft
Journal of Geophysical Research, 2004Co-Authors: L. A. Frank, W. R. PatersonAbstract:[1] Measurements of electron beams and thermal ions were achieved by the Galileo Spacecraft during the later phases of its mission for three outbound passages of the local afternoon and noon sectors of Jupiter's magnetosphere. During the first two passages the Spacecraft passed through the rigidly corotating plasma torus with outer boundary near 8 RJ, into the transition region from torus to plasma sheet, and then into the plasma sheet proper at distances beyond ∼25 RJ. Telemetry coverage for the third passage began in the transition region. At the outer boundary of the torus the ion densities and temperatures were ∼500 cm−3 and 106 K. In the transition region the ion densities decreased with increasing distance to 0.1 cm−3, and temperatures increased to 5 × 107 K. In the plasma sheet the ion densities were typically 0.1 cm−3 with temperatures of 108 K. The azimuthal component of plasma flow slows to ∼70% of the corotational value in the transition region. For the first two passages, strong radial flows toward Jupiter increase with increasing radial distances. For the third passage near local noon the plasma flows are considerably more stagnant than those at local evening. The variations in the flow suggest that the solar wind influence extends to radial distances in the range of 10 RJ. Electron beams parallel and antiparallel to the magnetic field were observed during the passages on field lines connected to the main auroral ring in the ionosphere. Major constraints on the heating/acceleration mechanism for the main ring are (1) the presence of the electron beams at and near the equator and (2) previous remote observations of emissions in the vicinity of the atmospheric methane layer. These constraints support a heating mechanism in this layer driven by magnetospheric convection without acceleration by field-aligned electrostatic fields. At radial distances 30–44 RJ near local noon the plasma densities exhibited a System III effect, increasing once per planetary rotation near a longitude 300°. In addition, the finding of thermal ion beams directed parallel to the magnetic field near 20 RJ resolves the problem of radial force balance previously identified with Voyager measurements. That is, the outward centrifugal force for these beams is sufficient to balance the inward radial force of the magnetic field.
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plasmas observed with the Galileo Spacecraft during its flyby over io s northern polar region
Journal of Geophysical Research, 2002Co-Authors: L. A. Frank, W. R. PatersonAbstract:[1] On 8 August 2001 the tape recorder on board the Galileo Spacecraft provided high-resolution measurements of plasmas during a 1-hour interval centered on the closest approach to Io at an altitude of 200 km. During this period the Spacecraft trajectory was positioned at a radial distance from Jupiter of 5.9 RJ (Jupiter radii) and approached Io from upstream in the torus plasma flow, then over the northern polar region of Io, and subsequently into the downstream wake in the torus. The upstream and downstream ion densities as calculated from the moments of the measured three-dimensional velocity distributions were about 1200/cm3. These plasmas were rigidly corotating with Jupiter at 57 km/s. The upstream ions were characterized by the sum of four Maxwellian distributions, and the downstream distributions exhibited a similar set of thermal distributions with half the density of that found upstream and the remainder as pickup heavy ions freshly injected by the interaction of the torus flow with Io's ionosphere/atmosphere. The boundary of the Hill (Lagrange) sphere for Io's neutral gases which were co-orbiting with this moon was about 5 RIo (Io radii) from its center as identified by the onset of decreasing number densities and bulk flow speed as the Spacecraft approached Io. Closer to Io, and just before its entry and departure from magnetic field lines intercepting its northern polar surface, the diversion of incoming torus plasma by Io's face toward this flow and the subsequent downstream flow around Io were observed. Over Io's polar cap the torus plasma density was reduced by a factor of about 5 relative to that measured upstream and downstream from the Io interaction. The bulk flow speeds of the torus plasma were reduced to several km/s, an effect that is expected for the slow transport of magnetic flux in Io's conducting interior. A unique set of conditions allowed the detection of a cooler ion species with extremely high values of mass/charge in the range of 500 to 1000 amu. These ions are interpreted as clusters of SO2 molecules, or SO2 “snowflakes,” which briefly exist from the fresh injection and subsequent cooling of volcanic gases.
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passage through lo s ionospheric plasmas by the Galileo Spacecraft
Journal of Geophysical Research, 2001Co-Authors: L. A. Frank, W. R. PatersonAbstract:On February 22, 2000, the Galileo Spacecraft passed by the moon Io at a closest approach distance of 206 km. This altitude was sufficiently low that the plasma analyzer observed the three-dimensional ion velocity distributions as functions of energy/charge (E/Q) at the top of Io's ionosphere. The ionospheric ion distributions consisted of two populations, a warm distribution with density and temperature of ∼8000 cm -3 and 10,000 K and a cool population with 3000 cm -3 and 2300 K. This cooler temperature is in the range of those observed remotely for some volcanic plumes. The bulk speed of these ions was 2 km s -1 with respect to Io's surface. In order to identify the mass/unit charge (M/Q) of the ionospheric ions, the E/Q spectra of the pickup ions in this region were examined. The most probable M/Q of the primary population of these ions was inferred to be 64. Remote spectroscopic observations of Io's surface and atmosphere suggest that these ions are S 2 + and/or SO 2 + , although SO + and SO 3 + are not eliminated as possibilities. There is some evidence for lesser densities of heavier ions such as S 3 + and S 4 + . The densities, temperatures, and bulk flow velocities of torus ions were measured as the Spacecraft approached Io from the upstream direction. A combination of fits to the E/Q spectra observed with Galileo, the determinations of the M/Q of the primary ions with the plasma instrumentation on this Spacecraft during other passages, and the previous identification of the primary ions with Voyager 1 plasma and remote observations find the following primary composition for the unperturbed torus near Io: O ++ (50 cm -3 , 30 eV), O + (200 cm -3 , 30 eV), S ++ (400 cm -3 , 90 eV), and S + (100 cm -3 , 90 eV). At a radial distance from Io of ∼19,700 km (10.9 Io radii), changes in the torus ion density, temperature, and bulk flow velocity provide evidence that a cloud of neutral gases is co-orbiting with Io and is providing a substantial interaction with the torus ions.
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survey of thermal ions in the io plasma torus with the Galileo Spacecraft
Journal of Geophysical Research, 2001Co-Authors: L. A. Frank, W. R. PatersonAbstract:The densities, temperatures, and bulk flow velocities are reported for a series of six passages of the Galileo Spacecraft through Io's torus in Jupiter's magnetosphere. These observations were gained with the plasma analyzers on December 7, 1995, and July 1–2, August 12, September 14, October 11, and November 25, all of the latter in 1999. These plasma analyzers provided high-resolution measurements of the energy/charge (E/Q) spectra of the three-dimensional velocity distributions of the thermal ions that included determinations of the mass/charge (M/Q) of the primary ions with a mass spectrometer. The four dominant ions in the hot torus were two populations of ions with M/Q = 16 and two smaller populations with M/Q = 8 and 32, respectively. The identification of these four ions was based upon a best fit to the E/Q spectra of the measured three-dimensional ion velocity distributions. The two distributions with M/Q =16 were characterized by two different temperatures, in the ranges of 20 to 30 eV and 60 to 80 eV, respectively. On the basis of expectations of higher temperatures with higher masses for the pickup ions the cooler population is identified as O+, and the hotter as S++. The two smaller populations with M/Q = 8 and 32 are identified as O++ and S+, respectively. The temperatures were ∼20 eV for the O++ and 60 to 80 eV for the S+. The densities and temperatures of the ions in the hot torus remained constant during the period July through November 1999. However, the ion densities during the initial passage on December 7, 1995, were greater by factors of ∼3, which support the presence of long-term density variations of the torus plasmas but with relatively small fluctuations in the temperatures. A complete survey of System III longitudes was acquired with the set of six passages. The presence of an “active sector” at longitudes in the approximate range of 180° to 230° as originally found with remote observations of the torus brightnesses is confirmed with these Galileo measurements. In addition, further evidence for the importance of interchange motions for radial plasma transport was also evident in several of the Galileo passages, a dynamical process which was first identified in fields and particles measurements during the first passage through the torus on December 7, 1995. A persistent lag with an average in the range of ∼2 to 4 km/s in the azimuthal flows relative to that for rigid corotation was detected and supports the previously proposed System IV coordinate system that has a slightly slower rotation rate relative to that for System III.
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return to io by the Galileo Spacecraft plasma observations
Journal of Geophysical Research, 2000Co-Authors: L. A. Frank, W. R. PatersonAbstract:On October 11, 1999, a series of high-resolution plasma measurements were obtained during the second close flyby of Io of the Galileo mission. The closest approach to Io occurred at an altitude of 617 km along the flank of Jupiter's torus plasma flows past this moon. Energy/charge (E/Q) and mass/charge (M/Q) measurements with the plasma analyzer were used to identify the primary ions. At closest approach the ion number densities increased to their maximum values of 1200 cm -3 as calculated from the plasma moments. These ions were dominated by two thermal populations of torus ions with M/Q = 16, one with density and temperature of 800 cm -3 and kT= 40 eV and the other with 200 cm -3 and 160 eV. On the basis of the previous Voyager 1 remote measurements with a spectrometer, these two thermal ion plasmas are identified as O + and S ++ , respectively. A substantial population of pickup ions was also observed, with densities of about 100 cm -3 each for S + and SO + . The plasma bulk flows were strongly deflected around the body of Io, and the speed of the bulk flow increased to a factor of 1.3 greater than that for rigid corotational flow. The torus ion densities just outside of Io's orbit were about 800 cm -3 , These densities at the immediate position of Io are smaller by a factor of about 4 relative to those during the first flyby on December 7, 1995, but should not be taken as indicative of a similar decrease in the bulk of the plasma torus. Two major plasma regimes were encountered before the closest approach to Io. The first was a region of hot ions located inside of Io's orbit which was previously identified as the ribbon of enhanced plasma densities with Voyager 1 plasma measurements and with ground-based imagery. The ion composition in the ribbon included O + and S ++ . The second region, closer to Io, exhibited a hot torus plasma which was mixed with pickup hydrogen ions. These hydrogen ions were detected at distances beginning at 7.8 RIo from this moon, which were generally inside the Hill (Lagrange) sphere for Io's atmosphere.
M G Kivelson - One of the best experts on this subject based on the ideXlab platform.
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evidence of a global magma ocean in io s interior
Science, 2011Co-Authors: K K Khurana, M G Kivelson, Xianzhe Jia, F Nimmo, Gerald Schubert, C T RussellAbstract:Extensive volcanism and high-temperature lavas hint at a global magma reservoir in Io, but no direct evidence has been available. We exploited Jupiter's rotating magnetic field as a sounding signal and show that the magnetometer data collected by the Galileo Spacecraft near Io provide evidence of electromagnetic induction from a global conducting layer. We demonstrate that a completely solid mantle provides insufficient response to explain the magnetometer observations, but a global subsurface magma layer with a thickness of over 50 kilometers and a rock melt fraction of 20% or more is fully consistent with the observations. We also place a stronger upper limit of about 110 nanoteslas (surface equatorial field) on the dynamo dipolar field generated inside Io.
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jovian plasma sheet morphology particle and field observations by the Galileo Spacecraft
Planetary and Space Science, 2005Co-Authors: Lara Waldrop, K K Khurana, M G Kivelson, N Krupp, T A Fritz, A LaggAbstract:Abstract We present results from an investigation of the plasma sheet encounter signatures observed in the Jovian magnetosphere by the Energetic Particles Detector (EPD) and Magnetometer (MAG) onboard the Galileo Spacecraft. Maxima in ion flux were used to identify over 500 Spacecraft encounters with the plasma sheet between radial distances from Jupiter from 20 to 140 R J during the first 25 orbits (4 years of data). Typical signatures of plasma sheet encounters show a characteristic periodicity of either 5 or 10 hours that is attributed to an oscillation in the relative distance between the Spacecraft and the plasma sheet that arises from the combination of planetary rotation and offset magnetic and rotational axes. However, the energetic particle and field data also display much variability, including instances of intense fluxes having little to no periodicity that persist for several Jovian rotation periods. Abrupt changes in the mean distance between the plasma sheet and the Spacecraft are suggested to account for some of the transitions between typical flux periodicities associated with plasma sheet encounters. Additional changes in the plasma sheet thickness and/or amplitude of the plasma sheet displacement from the location of the Spacecraft are required to explain the cases where the periodicity breaks down but fluxes remain high. These changes in plasma sheet characteristics do not display an obvious periodicity; however, the observations suggest that dawn/dusk asymmetries in both the structure of the plasma sheet and the frequency of anomalous plasma sheet encounters are present. Evidence of a thin, well-ordered plasma sheet is found out to 110 R J in the dawn and midnight local time sectors, while the dusk magnetosphere is characterized by a thicker, more disordered plasma sheet and has a potentially more pronounced response to an impulsive trigger. Temporal variations associated with changing solar wind conditions are suggested to account for the anomalous plasma sheet encounters there.
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Galileo magnetometer measurements a stronger case for a subsurface ocean at europa
Science, 2000Co-Authors: M G Kivelson, K K Khurana, C T Russell, Raymond J Walker, M Volwerk, Christophe ZimmerAbstract:On 3 January 2000, the Galileo Spacecraft passed close to Europa when it was located far south of Jupiter's magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward Jupiter. This pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of Europa's internal field. The Galileo magnetometer measured changes in the magnetic field predicted if a current-carrying outer shell, such as a planet-scale liquid ocean, is present beneath the icy surface. The evidence that Europa's field varies temporally strengthens the argument that a liquid ocean exists beneath the present-day surface.
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the magnetic fields of the galilean moons of jupiter the Galileo Spacecraft magnetometer results
The Three Galileos the Man the Spacecraft the Telescope, 1998Co-Authors: D J Southwood, M G KivelsonAbstract:We review magnetic field measurements from flybys of the Galilean moons. Large or at least detectable magnetic perturbations during flybys were expected. Intrinsic fields were not. Ganymede has an intrinsic field, as probably do Io and Europa, constituting a major discovery in planetary science.
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absence of an internal magnetic field at callisto
Nature, 1997Co-Authors: K K Khurana, M G Kivelson, C T Russell, Raymond J Walker, D J SouthwoodAbstract:Little is known about the internal properties of Callisto—the outermost of Jupiter's four large galilean moons—other than the average density (about 1.8gem-3). The recent unexpected discovery1–4 that Ganymede, and perhaps Io, has an internally generated magnetic field, combined with gravity results5,6 suggesting that both Ganymede and Io are internally differentiated with metallic cores and rocky mantles, has heightened anticipation of the results obtained by the Galileo Spacecraft in its recent fly-by of Callisto. Here we report that the Spacecraft, passing the moon at a distance of only ∼1,100 km from the surface, detected only a small enhancement of the field strength (∼7nT), which maybe related to changes in the jovian plasma environment caused by Callisto7. Callisto does not have an internally generated magnetic field.
D J Southwood - One of the best experts on this subject based on the ideXlab platform.
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the magnetic fields of the galilean moons of jupiter the Galileo Spacecraft magnetometer results
The Three Galileos the Man the Spacecraft the Telescope, 1998Co-Authors: D J Southwood, M G KivelsonAbstract:We review magnetic field measurements from flybys of the Galilean moons. Large or at least detectable magnetic perturbations during flybys were expected. Intrinsic fields were not. Ganymede has an intrinsic field, as probably do Io and Europa, constituting a major discovery in planetary science.
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absence of an internal magnetic field at callisto
Nature, 1997Co-Authors: K K Khurana, M G Kivelson, C T Russell, Raymond J Walker, D J SouthwoodAbstract:Little is known about the internal properties of Callisto—the outermost of Jupiter's four large galilean moons—other than the average density (about 1.8gem-3). The recent unexpected discovery1–4 that Ganymede, and perhaps Io, has an internally generated magnetic field, combined with gravity results5,6 suggesting that both Ganymede and Io are internally differentiated with metallic cores and rocky mantles, has heightened anticipation of the results obtained by the Galileo Spacecraft in its recent fly-by of Callisto. Here we report that the Spacecraft, passing the moon at a distance of only ∼1,100 km from the surface, detected only a small enhancement of the field strength (∼7nT), which maybe related to changes in the jovian plasma environment caused by Callisto7. Callisto does not have an internally generated magnetic field.
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discovery of ganymede s magnetic field by the Galileo Spacecraft
Nature, 1996Co-Authors: M G Kivelson, K K Khurana, C T Russell, D J Southwood, F. V. Coroniti, R J Walker, J Warnecke, C Polanskey, G SchubertAbstract:THE Galileo Spacecraft has now passed close to Jupiter's largest moon—Ganymede—on two occasions, the first at an altitude of 838 km, and the second at an altitude of just 264 km. Here we report the discovery during these encounters of an internal magnetic field associated with Ganymede (the only other solid bodies in the Solar System known to have magnetic fields are Mercury, Earth and probably lo1). The data are consistent with a Ganymede-centred magnetic dipole tilted by ∼10° relative to the spin axis, and an equatorial surface-field strength of ∼750 nT. The magnetic field is strong enough to carve out a magnetosphere with clearly defined boundaries within Jupiter's magnetosphere. Although the observations require an internal field, they do not indicate its source. But the existence of an internal magnetic field should in itself help constrain models of Ganymede's interior.
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a magnetic signature at io initial report from the Galileo magnetometer
Science, 1996Co-Authors: M G Kivelson, K K Khurana, C T Russell, Raymond J Walker, D J Southwood, J A Linker, C PolanskeyAbstract:During the inbound pass of the Galileo Spacecraft, the magnetometer acquired 1 minute averaged measurements of the magnetic field along the trajectory as the Spacecraft flew by Io. A field decrease, of nearly 40 percent of the background jovian field at closest approach to Io, was recorded. Plasma sources alone appear incapable of generating perturbations as large as those observed and an induced source for the observed moment implies an amount of free iron in the mantle much greater than expected. On the other hand, an intrinsic magnetic field of amplitude consistent with dynamo action at Io would explain the observations. It seems plausible that Io, like Earth and Mercury, is a magnetized solid planet.
K K Khurana - One of the best experts on this subject based on the ideXlab platform.
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evidence of a global magma ocean in io s interior
Science, 2011Co-Authors: K K Khurana, M G Kivelson, Xianzhe Jia, F Nimmo, Gerald Schubert, C T RussellAbstract:Extensive volcanism and high-temperature lavas hint at a global magma reservoir in Io, but no direct evidence has been available. We exploited Jupiter's rotating magnetic field as a sounding signal and show that the magnetometer data collected by the Galileo Spacecraft near Io provide evidence of electromagnetic induction from a global conducting layer. We demonstrate that a completely solid mantle provides insufficient response to explain the magnetometer observations, but a global subsurface magma layer with a thickness of over 50 kilometers and a rock melt fraction of 20% or more is fully consistent with the observations. We also place a stronger upper limit of about 110 nanoteslas (surface equatorial field) on the dynamo dipolar field generated inside Io.
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jovian plasma sheet morphology particle and field observations by the Galileo Spacecraft
Planetary and Space Science, 2005Co-Authors: Lara Waldrop, K K Khurana, M G Kivelson, N Krupp, T A Fritz, A LaggAbstract:Abstract We present results from an investigation of the plasma sheet encounter signatures observed in the Jovian magnetosphere by the Energetic Particles Detector (EPD) and Magnetometer (MAG) onboard the Galileo Spacecraft. Maxima in ion flux were used to identify over 500 Spacecraft encounters with the plasma sheet between radial distances from Jupiter from 20 to 140 R J during the first 25 orbits (4 years of data). Typical signatures of plasma sheet encounters show a characteristic periodicity of either 5 or 10 hours that is attributed to an oscillation in the relative distance between the Spacecraft and the plasma sheet that arises from the combination of planetary rotation and offset magnetic and rotational axes. However, the energetic particle and field data also display much variability, including instances of intense fluxes having little to no periodicity that persist for several Jovian rotation periods. Abrupt changes in the mean distance between the plasma sheet and the Spacecraft are suggested to account for some of the transitions between typical flux periodicities associated with plasma sheet encounters. Additional changes in the plasma sheet thickness and/or amplitude of the plasma sheet displacement from the location of the Spacecraft are required to explain the cases where the periodicity breaks down but fluxes remain high. These changes in plasma sheet characteristics do not display an obvious periodicity; however, the observations suggest that dawn/dusk asymmetries in both the structure of the plasma sheet and the frequency of anomalous plasma sheet encounters are present. Evidence of a thin, well-ordered plasma sheet is found out to 110 R J in the dawn and midnight local time sectors, while the dusk magnetosphere is characterized by a thicker, more disordered plasma sheet and has a potentially more pronounced response to an impulsive trigger. Temporal variations associated with changing solar wind conditions are suggested to account for the anomalous plasma sheet encounters there.
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Galileo magnetometer measurements a stronger case for a subsurface ocean at europa
Science, 2000Co-Authors: M G Kivelson, K K Khurana, C T Russell, Raymond J Walker, M Volwerk, Christophe ZimmerAbstract:On 3 January 2000, the Galileo Spacecraft passed close to Europa when it was located far south of Jupiter's magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward Jupiter. This pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of Europa's internal field. The Galileo magnetometer measured changes in the magnetic field predicted if a current-carrying outer shell, such as a planet-scale liquid ocean, is present beneath the icy surface. The evidence that Europa's field varies temporally strengthens the argument that a liquid ocean exists beneath the present-day surface.
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absence of an internal magnetic field at callisto
Nature, 1997Co-Authors: K K Khurana, M G Kivelson, C T Russell, Raymond J Walker, D J SouthwoodAbstract:Little is known about the internal properties of Callisto—the outermost of Jupiter's four large galilean moons—other than the average density (about 1.8gem-3). The recent unexpected discovery1–4 that Ganymede, and perhaps Io, has an internally generated magnetic field, combined with gravity results5,6 suggesting that both Ganymede and Io are internally differentiated with metallic cores and rocky mantles, has heightened anticipation of the results obtained by the Galileo Spacecraft in its recent fly-by of Callisto. Here we report that the Spacecraft, passing the moon at a distance of only ∼1,100 km from the surface, detected only a small enhancement of the field strength (∼7nT), which maybe related to changes in the jovian plasma environment caused by Callisto7. Callisto does not have an internally generated magnetic field.
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discovery of ganymede s magnetic field by the Galileo Spacecraft
Nature, 1996Co-Authors: M G Kivelson, K K Khurana, C T Russell, D J Southwood, F. V. Coroniti, R J Walker, J Warnecke, C Polanskey, G SchubertAbstract:THE Galileo Spacecraft has now passed close to Jupiter's largest moon—Ganymede—on two occasions, the first at an altitude of 838 km, and the second at an altitude of just 264 km. Here we report the discovery during these encounters of an internal magnetic field associated with Ganymede (the only other solid bodies in the Solar System known to have magnetic fields are Mercury, Earth and probably lo1). The data are consistent with a Ganymede-centred magnetic dipole tilted by ∼10° relative to the spin axis, and an equatorial surface-field strength of ∼750 nT. The magnetic field is strong enough to carve out a magnetosphere with clearly defined boundaries within Jupiter's magnetosphere. Although the observations require an internal field, they do not indicate its source. But the existence of an internal magnetic field should in itself help constrain models of Ganymede's interior.
