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Mitchell DG, Perry ME, Hamilton DC, Westlake JH, Kollmann P, Smith HT, Carbary JF, Waite JH, Perryman R, Hsu HW, Wahlund JE, Morooka MW, Hadid LZ, Persoon AM, Kurth WS. Dust grains fall from Saturn’s D-ring into its equatorial upper atmosphere. Science 2018; 362:362/6410/eaat2236. [DOI: 10.1126/science.aat2236] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 09/06/2018] [Indexed: 11/02/2022]
Abstract
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.
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Wahlund JE, Morooka MW, Hadid LZ, Persoon AM, Farrell WM, Gurnett DA, Hospodarsky G, Kurth WS, Ye SY, Andrews DJ, Edberg NJT, Eriksson AI, Vigren E. In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings. Science 2017; 359:66-68. [PMID: 29229651 DOI: 10.1126/science.aao4134] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 11/27/2017] [Indexed: 11/02/2022]
Abstract
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.
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Affiliation(s)
- J-E Wahlund
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
| | - M W Morooka
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - L Z Hadid
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - A M Persoon
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - W M Farrell
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
| | - D A Gurnett
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - G Hospodarsky
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - W S Kurth
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - S-Y Ye
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - D J Andrews
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - N J T Edberg
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - A I Eriksson
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - E Vigren
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
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Andersson L, Weber TD, Malaspina D, Crary F, Ergun RE, Delory GT, Fowler CM, Morooka MW, McEnulty T, Eriksson AI, Andrews DJ, Horanyi M, Collette A, Yelle R, Jakosky BM. Dust observations at orbital altitudes surrounding Mars. Science 2015; 350:aad0398. [PMID: 26542578 DOI: 10.1126/science.aad0398] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Dust is common close to the martian surface, but no known process can lift appreciable concentrations of particles to altitudes above ~150 kilometers. We present observations of dust at altitudes ranging from 150 to above 1000 kilometers by the Langmuir Probe and Wave instrument on the Mars Atmosphere and Volatile Evolution spacecraft. Based on its distribution, we interpret this dust to be interplanetary in origin. A comparison with laboratory measurements indicates that the dust grain size ranges from 1 to 12 micrometers, assuming a typical grain velocity of ~18 kilometers per second. These direct observations of dust entering the martian atmosphere improve our understanding of the sources, sinks, and transport of interplanetary dust throughout the inner solar system and the associated impacts on Mars's atmosphere.
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Affiliation(s)
- L Andersson
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA.
| | - T D Weber
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - D Malaspina
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - F Crary
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - R E Ergun
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - G T Delory
- Space Science Laboratory, University of California-Berkeley, Berkeley, CA 94720, USA
| | - C M Fowler
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - M W Morooka
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - T McEnulty
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - A I Eriksson
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - D J Andrews
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - M Horanyi
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - A Collette
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
| | - R Yelle
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
| | - B M Jakosky
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO 80303, USA
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Morooka MW, Wahlund JE, Eriksson AI, Farrell WM, Gurnett DA, Kurth WS, Persoon AM, Shafiq M, André M, Holmberg MKG. Dusty plasma in the vicinity of Enceladus. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja017038] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Wahlund JE, Boström R, Gustafsson G, Gurnett DA, Kurth WS, Pedersen A, Averkamp TF, Hospodarsky GB, Persoon AM, Canu P, Neubauer FM, Dougherty MK, Eriksson AI, Morooka MW, Gill R, André M, Eliasson L, Müller-Wodarg I. Cassini measurements of cold plasma in the ionosphere of Titan. Science 2005; 308:986-9. [PMID: 15894529 DOI: 10.1126/science.1109807] [Citation(s) in RCA: 158] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP) sensor observed the cold plasma environment around Titan during the first two flybys. The data show that conditions in Saturn's magnetosphere affect the structure and dynamics deep in the ionosphere of Titan. The maximum measured ionospheric electron number density reached 3800 per cubic centimeter near closest approach, and a complex chemistry was indicated. The electron temperature profiles are consistent with electron heat conduction from the hotter Titan wake. The ionospheric escape flux was estimated to be 10(25) ions per second.
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Affiliation(s)
- J E Wahlund
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
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