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The low-frequency source of Saturns kilometric radiation (2018)

Lamy, L., Zarka, P., Cecconi, B., Prange, R., Kurth, W. S., Hospodarsky, G., Persoon, A., Morooka, M., Wahlund, J.- E., Hunt, G. J.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-10-05

Beschreibung: Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn’s kilometric radiation (SKR) has been widely used as a remote proxy of Saturn’s magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6– to 12–kilo–electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.

Schlagwort(e): Geochemistry, Geophysics, Online Only, Planetary Science

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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In situ collection of dust grains falling from Saturns rings into its atmosphere (2018)

Hsu, H.-W., Schmidt, J., Kempf, S., Postberg, F., Moragas-Klostermeyer, G., Seiss, M., Hoffmann, H., Burton, M., Ye, S., Kurth, W. S., Horanyi, M., Khawaja, N., Spahn, F., Schirdewahn, D., ODonoghue, J., Moore, L., Cuzzi, J., Jones, G. H., Srama, R.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-10-05

Beschreibung: Saturn’s main rings are composed of 〉95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft’s traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn’s dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred "ring rain." Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings.

Schlagwort(e): Geochemistry, Geophysics, Online Only, Planetary Science

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Chemical interactions between Saturns atmosphere and its rings (2018)

Waite, J. H., Perryman, R. S., Perry, M. E., Miller, K. E., Bell, J., Cravens, T. E., Glein, C. R., Grimes, J., Hedman, M., Cuzzi, J., Brockwell, T., Teolis, B., Moore, L., Mitchell, D. G., Persoon, A., Kurth, W. S., Wahlund, J.- E., Morooka, M., Hadid, L. Z., Chocron, S., Walker, J., Nagy, A., Yelle, R., Ledvina, S., Johnson, R., Tseng, W., Tucker, O. J., Ip, W.- H.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-10-05

Beschreibung: The Pioneer and Voyager spacecraft made close-up measurements of Saturn’s ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn’s atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft’s Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H 2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

Schlagwort(e): Atmospheric Science, Online Only, Planetary Science

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Dust grains fall from Saturns D-ring into its equatorial upper atmosphere (2018)

Mitchell, D. G., Perry, M. E., Hamilton, D. C., Westlake, J. H., Kollmann, P., Smith, H. T., Carbary, J. F., Waite, J. H., Perryman, R., Hsu, H.- W., Wahlund, J.- E., Morooka, M. W., Hadid, L. Z., Persoon, A. M., Kurth, W. S.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-10-05

Beschreibung: The sizes of Saturn’s ring particles range from meters (boulders) to nanometers (dust). Determination of the rings’ ages depends on loss processes, including the transport of dust into Saturn’s atmosphere. During the Grand Finale orbits of the Cassini spacecraft, its instruments measured tiny dust grains that compose the innermost D-ring of Saturn. The nanometer-sized dust experiences collisions with exospheric (upper atmosphere) hydrogen and molecular hydrogen, which forces it to fall from the ring into the ionosphere and lower atmosphere. We used the Magnetospheric Imaging Instrument to detect and characterize this dust transport and also found that diffusion dominates above and near the altitude of peak ionospheric density. This mechanism results in a mass deposition into the equatorial atmosphere of ~5 kilograms per second, constraining the age of the D-ring.

Schlagwort(e): Geochemistry, Geophysics, Online Only, Planetary Science

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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In situ measurements of Saturns ionosphere show that it is dynamic and interacts with the rings (2018)

Wahlund, J.- E., Morooka, M. W., Hadid, L. Z., Persoon, A. M., Farrell, W. M., Gurnett, D. A., Hospodarsky, G., Kurth, W. S., Ye, S.- Y., Andrews, D. J., Edberg, N. J. T., Eriksson, A. I., Vigren, E.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-01-05

Beschreibung: The ionized upper layer of Saturn’s atmosphere, its ionosphere, provides a closure of currents mediated by the magnetic field to other electrically charged regions (for example, rings) and hosts ion-molecule chemistry. In 2017, the Cassini spacecraft passed inside the planet’s rings, allowing in situ measurements of the ionosphere. The Radio and Plasma Wave Science instrument detected a cold, dense, and dynamic ionosphere at Saturn that interacts with the rings. Plasma densities reached up to 1000 cubic centimeters, and electron temperatures were below 1160 kelvin near closest approach. The density varied between orbits by up to two orders of magnitude. Saturn’s A- and B-rings cast a shadow on the planet that reduced ionization in the upper atmosphere, causing a north-south asymmetry.

Schlagwort(e): Geochemistry, Geophysics, Planetary Science

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Jupiters magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits (2017)

Connerney, J. E. P., Adriani, A., Allegrini, F., Bagenal, F., Bolton, S. J., Bonfond, B., Cowley, S. W. H., Gerard, J.- C., Gladstone, G. R., Grodent, D., Hospodarsky, G., Jorgensen, J. L., Kurth, W. S., Levin, S. M., Mauk, B., McComas, D. J., Mura, A., Paranicas, C., Smith, E. J., Thorne, R. M., Valek, P., Waite, J.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2017-05-26

Beschreibung: The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno’s capture orbit spanned the jovian magnetosphere from bow shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno’s passage over the poles and traverse of Jupiter’s hazardous inner radiation belts. Juno’s energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator.

Schlagwort(e): Astronomy

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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