%0 Journal Article %1 Kivelson2001 %A Kivelson, M. G. %A Khurana, K. K. %A Russell, C. T. %A Joy, S. P. %A Volwerk, M. %A Walker, R. J. %A Zimmer, C. %A Linker, J. A. %D 2001 %J Journal of Geophysical Research-SPACE PHYSICS %K ANALYSIS; CURRENT CYCLOTRON DISPERSION ENVIRONMENT; EUROPA FIELD; MAGNETOMETER; MIRROR-MODE PLASMA SPACECRAFT; STRUCTURES; SYSTEM; TORUS; WAVE WAVES; %N A11 %P 26121--26135 %T Magnetized or unmagnetized: Ambiguity persists following Galileo's encounters with Io in 1999 and 2000 %V 106 %X Magnetometer data from Galileo's close encounters with lo on October 11, 1999, and February 22, 2000, do not establish clearly either the existence or absence of an internal magnetic moment because they were acquired in regions where plasma currents contribute large magnetic perturbations. Data from an additional encounter on November 26, 1999, with closest approach beneath lo's south polar regions, were lost. The recent passes add to our understanding of the interaction of the torus with lo and its flux tube and tighten the limits on possible internal sources of magnetic fields. Simple field-draping arguments account for some aspects of the observed rotations. Interpretations in terms of both a magnetized and an unmagnetized lo are considered. Data from the February 2000 pass (closest approach altitude 201 km, latitude 18 degrees) rule out a strongly magnetized lo (surface equatorial field larger than the background field) but do not rule out a weakly magnetized lo (surface equatorial field of the order of Ganymede's but smaller than the background field at Io). Models suggest that if Io is magnetized, its magnetic moment is not strictly antialigned with the rotation axis. The inferred tilt is consistent with contributions from an inductive field analogous to that observed at Europa and Callisto. If an induced field is present, the currents would flow in the outer mantle or aesthenosphere. Wave perturbations differ on flux tubes that do or do not link directly to lo and its ionosphere suggesting that the latter flux tubes are virtually stagnant in lo's frame and that a unipolar inductor appropriately models the currents linking Io to Jupiter's ionosphere.

@article{Kivelson2001, abstract = {Magnetometer data from Galileo's close encounters with lo on October 11, 1999, and February 22, 2000, do not establish clearly either the existence or absence of an internal magnetic moment because they were acquired in regions where plasma currents contribute large magnetic perturbations. Data from an additional encounter on November 26, 1999, with closest approach beneath lo's south polar regions, were lost. The recent passes add to our understanding of the interaction of the torus with lo and its flux tube and tighten the limits on possible internal sources of magnetic fields. Simple field-draping arguments account for some aspects of the observed rotations. Interpretations in terms of both a magnetized and an unmagnetized lo are considered. Data from the February 2000 pass (closest approach altitude 201 km, latitude 18 degrees) rule out a strongly magnetized lo (surface equatorial field larger than the background field) but do not rule out a weakly magnetized lo (surface equatorial field of the order of Ganymede's but smaller than the background field at Io). Models suggest that if Io is magnetized, its magnetic moment is not strictly antialigned with the rotation axis. The inferred tilt is consistent with contributions from an inductive field analogous to that observed at Europa and Callisto. If an induced field is present, the currents would flow in the outer mantle or aesthenosphere. Wave perturbations differ on flux tubes that do or do not link directly to lo and its ionosphere suggesting that the latter flux tubes are virtually stagnant in lo's frame and that a unipolar inductor appropriately models the currents linking Io to Jupiter's ionosphere.}, added-at = {2009-11-03T20:21:25.000+0100}, author = {Kivelson, M. G. and Khurana, K. K. and Russell, C. T. and Joy, S. P. and Volwerk, M. and Walker, R. J. and Zimmer, C. and Linker, J. A.}, biburl = {https://www.bibsonomy.org/bibtex/278d6153463d6fd81b17934e6f8478d8a/svance}, citedreferences = {ACUNA MH, 1981, J GEO R-S P, V86, P8513 ; COMBI MR, 1998, J GEOPHYS RES-SPACE, V103, P9071 ; CRARY FJ, 1997, GEOPHYS RES LETT, V24, P2135 ; FRANK LA, 1996, Science, V274, P394 ; FRANK LA, 2000, J GEOPHYS RES-SPACE, V105, P25363 ; GOERTZ CK, 1980, J GEOPHYS RES, V85, P2949 ; GOLDREICH P, 1969, ASTROPHYS J, V156, P59 ; GURNETT DA, 1996, Science, V274, P391 ; HILL TW, 1983, PHYSICS JOVIAN MAGNE, P353 ; HILL TW, 1998, J GEOPHYS RES-PLANET, V103, P19879 ; HUDDLESTON DE, 1997, GEOPHYS RES LETT, V24, P2143 ; HUDDLESTON DE, 1998, J GEOPHYS RES-PLANET, V103, P19887 ; HUDDLESTON DE, 1999, J GEOPHYS RES-SPACE, V104, P17479 ; KHURANA KK, 1997, GEOPHYS RES LETT, V24, P2391 ; KHURANA KK, 1998, GEOPHYS RES LETT, V25, P2351 ; KIVELSON MG, 1992, SPACE SCI REV, V60, P357 ; KIVELSON MG, 1996, Nature, V384, P537 ; KIVELSON MG, 1996, Science, V273, P337 ; KIVELSON MG, 1996, Science, V274, P396 ; KIVELSON MG, 1999, J GEOPHYS RES-SPACE, V104, P4609 ; KIVELSON MG, 2000, Science, V289, P1340 ; LINKER JA, 1991, J GEOPHYS RES, V96, P21037 ; LINKER JA, 1998, J GEOPHYS RES, V103, P19879 ; LINKER JA, 1999, EOS FALL M S T AGU, V80, F621 ; LUHMANN JG, 1995, INTRO SPACE PHYSICS, P203 ; NEUBAUER FM, 1980, J GEOPHYS RES, V85, P1171 ; NEUBAUER FM, 1998, GEOPHYS RES LETT, V25, P2349 ; NEUBAUER FM, 1998, J GEOPHYS RES-PLANET, V103, P19843 ; ROBERTS PH, 2000, REV MOD PHYS, V72, P1081 ; RUSSELL CT, 1999, J GEOPHYS RES-SPACE, V104, P17471 ; RUSSELL CT, 2000, ADV SPACE RES, V26, P1653 ; RUSSELL CT, 2000, Science, V287, P1998 ; RUSSELL CT, 2001, IN PRESS ADV SPACE R ; SAUR J, 1999, J GEOPHYS RES-SPACE, V104, P25105 ; SAUR J, 2000, GEOPHYS RES LETT, V27, P2893 ; SOUTHWOOD DJ, 1980, J GEOPHYS RES, V85, P5959 ; SPENCER JR, 1996, ANNU REV EARTH PL SC, V24, P125 ; WARNECKE J, 1997, GEOPHYS RES LETT, V24, P2139 ; WILLIAMS DJ, 1996, Science, V274, P401 ; WILSON JE, 1999, J GEOPHYS RES-PLANET, V104, P16567 ; WOLFGLADROW DA, 1987, J GEOPHYS RES, V92, P9949 ; ZIMMER C, 2000, Icarus, V147, P329}, date-modified = {2007-12-04 11:28:47 -0800}, interhash = {a9786b1dfc8a83c30f362bbcb0aba355}, intrahash = {78d6153463d6fd81b17934e6f8478d8a}, journal = {Journal of Geophysical Research-SPACE PHYSICS}, keywords = {ANALYSIS; CURRENT CYCLOTRON DISPERSION ENVIRONMENT; EUROPA FIELD; MAGNETOMETER; MIRROR-MODE PLASMA SPACECRAFT; STRUCTURES; SYSTEM; TORUS; WAVE WAVES;}, number = {A11}, owner = {svance}, pages = {26121--26135}, timestamp = {2009-11-03T20:21:54.000+0100}, title = {Magnetized or unmagnetized: Ambiguity persists following Galileo's encounters with Io in 1999 and 2000}, volume = 106, year = 2001 }