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Weygand JM, Kivelson MG, Khurana KK, Schwarzl HK, Walker RJ, Balogh A, Kistler LM, Goldstein ML. Non-self-similar scaling of plasma sheet and solar wind probability distribution functions of magnetic field fluctuations. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2006ja011820] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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52
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Giampieri G, Dougherty MK, Smith EJ, Russell CT. A regular period for Saturn's magnetic field that may track its internal rotation. Nature 2006; 441:62-4. [PMID: 16672964 DOI: 10.1038/nature04750] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2006] [Accepted: 03/20/2006] [Indexed: 11/09/2022]
Abstract
The rotation rate of a planet is one of its fundamental properties. Saturn's rotation, however, is difficult to determine because there is no solid surface from which to time it, and the alternative 'clock'--the magnetic field--is nearly symmetrically aligned with the rotation axis. Radio emissions, thought to provide a proxy measure of the rotation of the magnetic field, have yielded estimates of the rotation period between 10 h 39 min 22 s and 10 h 45 min 45 s (refs 8-10). Because the period determined from radio measurements exhibits large time variations, even on timescales of months, it has been uncertain whether the radio-emission periodicity coincides with the inner rotation rate of the planet. Here we report magnetic field measurements that revealed a time-stationary magnetic signal with a period of 10 h 47 min 6 s +/- 40 s. The signal appears to be stable in period, amplitude and phase over 14 months of observations, pointing to a close connection with the conductive region inside the planet, although its interpretation as the 'true' inner rotation period is still uncertain.
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Affiliation(s)
- G Giampieri
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
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53
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Abstract
Instruments on the Cassini spacecraft reveal that a heat source within Saturn's moon Enceladus powers a great plume of water ice particles and dust grains, a geyser that jets outward from the south polar regions and most likely serves as the dominant source of Saturn's E ring. The interaction of flowing magnetospheric plasma with the plume modifies the particle and field environment of Enceladus. The structure of Saturn's magnetosphere, the extended region of space threaded by magnetic-field lines linked to the planet, is shaped by the ion source at Enceladus, and magnetospheric dynamics may be affected by the rate at which fresh ions are created.
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Affiliation(s)
- Margaret Galland Kivelson
- Institute of Geophysics and Planetary Physics and Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA.
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54
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Sittler EC, Blanc MF, Richardson JD. Proposed model for Saturn's auroral response to the solar wind: Centrifugal instability model. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005ja011191] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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55
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Achilleos N, Bertucci C, Russell CT, Hospodarsky GB, Rymer AM, Arridge CS, Burton ME, Dougherty MK, Hendricks S, Smith EJ, Tsurutani BT. Orientation, location, and velocity of Saturn's bow shock: Initial results from the Cassini spacecraft. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005ja011297] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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56
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Backes H, Neubauer FM, Dougherty MK, Achilleos N, André N, Arridge CS, Bertucci C, Jones GH, Khurana KK, Russell CT, Wennmacher A. Titan's Magnetic Field Signature During the First Cassini Encounter. Science 2005; 308:992-5. [PMID: 15890875 DOI: 10.1126/science.1109763] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The magnetic field signature obtained by Cassini during its first close encounter with Titan on 26 October 2004 is presented and explained in terms of an advanced model. Titan was inside the saturnian magnetosphere. A magnetic field minimum before closest approach marked Cassini's entry into the magnetic ionopause layer. Cassini then left the northern and entered the southern magnetic tail lobe. The magnetic field before and after the encounter was approximately constant for approximately 20 Titan radii, but the field orientation changed exactly at the location of Titan's orbit. No evidence of an internal magnetic field at Titan was detected.
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Affiliation(s)
- Heiko Backes
- Institut für Geophysik und Meteorologie, Universität zu Köln, Albertus Magnus Platz, 50678 Cologne, Germany.
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57
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Abstract
Since the Cassini spacecraft reached Saturn's orbit in 2004, its instruments have been sending back a wealth of data on the planet's magnetosphere (the region dominated by the magnetic field of the planet). In this Viewpoint, we discuss some of these results, which are reported in a collection of reports in this issue. The magnetosphere is shown to be highly variable and influenced by the planet's rotation, sources of plasma within the planetary system, and the solar wind. New insights are also gained into the chemical composition of the magnetosphere, with surprising results. These early results from Cassini's first orbit around Saturn bode well for the future as the spacecraft continues to orbit the planet.
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Affiliation(s)
- Tamas I Gombosi
- Center for Space Environment Modeling, Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
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58
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Gurnett DA, Kurth WS, Hospodarsky GB, Persoon AM, Averkamp TF, Cecconi B, Lecacheux A, Zarka P, Canu P, Cornilleau-Wehrlin N, Galopeau P, Roux A, Harvey C, Louarn P, Bostrom R, Gustafsson G, Wahlund JE, Desch MD, Farrell WM, Kaiser ML, Goetz K, Kellogg PJ, Fischer G, Ladreiter HP, Rucker H, Alleyne H, Pedersen A. Radio and Plasma Wave Observations at Saturn from Cassini's Approach and First Orbit. Science 2005; 307:1255-9. [PMID: 15604362 DOI: 10.1126/science.1105356] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We report data from the Cassini radio and plasma wave instrument during the approach and first orbit at Saturn. During the approach, radio emissions from Saturn showed that the radio rotation period is now 10 hours 45 minutes 45 +/- 36 seconds, about 6 minutes longer than measured by Voyager in 1980 to 1981. In addition, many intense impulsive radio signals were detected from Saturn lightning during the approach and first orbit. Some of these have been linked to storm systems observed by the Cassini imaging instrument. Within the magnetosphere, whistler-mode auroral hiss emissions were observed near the rings, suggesting that a strong electrodynamic interaction is occurring in or near the rings.
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Affiliation(s)
- D A Gurnett
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA.
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59
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Young DT, Berthelier JJ, Blanc M, Burch JL, Bolton S, Coates AJ, Crary FJ, Goldstein R, Grande M, Hill TW, Johnson RE, Baragiola RA, Kelha V, McComas DJ, Mursula K, Sittler EC, Svenes KR, Szegö K, Tanskanen P, Thomsen MF, Bakshi S, Barraclough BL, Bebesi Z, Delapp D, Dunlop MW, Gosling JT, Furman JD, Gilbert LK, Glenn D, Holmlund C, Illiano JM, Lewis GR, Linder DR, Maurice S, McAndrews HJ, Narheim BT, Pallier E, Reisenfeld D, Rymer AM, Smith HT, Tokar RL, Vilppola J, Zinsmeyer C. Composition and Dynamics of Plasma in Saturn's Magnetosphere. Science 2005; 307:1262-6. [PMID: 15731443 DOI: 10.1126/science.1106151] [Citation(s) in RCA: 257] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
During Cassini's initial orbit, we observed a dynamic magnetosphere composed primarily of a complex mixture of water-derived atomic and molecular ions. We have identified four distinct regions characterized by differences in both bulk plasma properties and ion composition. Protons are the dominant species outside about 9 RS (where RS is the radial distance from the center of Saturn), whereas inside, the plasma consists primarily of a corotating comet-like mix of water-derived ions with approximately 3% N+. Over the A and B rings, we found an ionosphere in which O2+ and O+ are dominant, which suggests the possible existence of a layer of O2 gas similar to the atmospheres of Europa and Ganymede.
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Affiliation(s)
- D T Young
- Southwest Research Institute, San Antonio, TX 78238, USA.
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60
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Krimigis SM, Mitchell DG, Hamilton DC, Krupp N, Livi S, Roelof EC, Dandouras J, Armstrong TP, Mauk BH, Paranicas C, Brandt PC, Bolton S, Cheng AF, Choo T, Gloeckler G, Hayes J, Hsieh KC, Ip WH, Jaskulek S, Keath EP, Kirsch E, Kusterer M, Lagg A, Lanzerotti LJ, Lavallee D, Manweiler J, McEntire RW, Rasmuss W, Saur J, Turner FS, Williams DJ, Woch J. Dynamics of Saturn's Magnetosphere from MIMI During Cassini's Orbital Insertion. Science 2005; 307:1270-3. [PMID: 15731445 DOI: 10.1126/science.1105978] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft observed the saturnian magnetosphere from January 2004 until Saturn orbit insertion (SOI) on 1 July 2004. The MIMI sensors observed frequent energetic particle activity in interplanetary space for several months before SOI. When the imaging sensor was switched to its energetic neutral atom (ENA) operating mode on 20 February 2004, at approximately 10(3) times Saturn's radius RS (0.43 astronomical units), a weak but persistent signal was observed from the magnetosphere. About 10 days before SOI, the magnetosphere exhibited a day-night asymmetry that varied with an approximately 11-hour periodicity. Once Cassini entered the magnetosphere, in situ measurements showed high concentrations of H+, H2+, O+, OH+, and H2O+ and low concentrations of N+. The radial dependence of ion intensity profiles implies neutral gas densities sufficient to produce high loss rates of trapped ions from the middle and inner magnetosphere. ENA imaging has revealed a radiation belt that resides inward of the D ring and is probably the result of double charge exchange between the main radiation belt and the upper layers of Saturn's exosphere.
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Affiliation(s)
- S M Krimigis
- Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA.
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61
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Jackman CM. Interplanetary conditions and magnetospheric dynamics during the Cassini orbit insertion fly-through of Saturn's magnetosphere. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005ja011054] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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