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Cosmic Dust Analyzer

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Cassini Cosmic Dust Detector, CDA

TheCosmic Dust Analyzer(CDA) on theCassini missionis a large-area (0.1 m2total sensitive area) multi-sensor dust instrument that includes a chemical dust analyzer (time-of-flight mass spectrometer), a highly reliableimpact ionizationdetector, and two high rate polarizedpolyvinylidene fluoride(PVDF) detectors. During 6 years en route toSaturnthe CDA analysed theinterplanetary dust cloud,the stream ofinterstellar dust,andJupiterdust streams. During 13 years in orbit around Saturn the CDA studied the E ring, dust in the plumes ofEnceladus,and dust inSaturn's environment.

Overview[edit]

Dust impacts on the Compositional Analyzer Target (CAT) of CDA and generated signals.

The Cosmic Dust Analyzer, CDA[1]was the seventh dust instrument from theMax Planck Institute for Nuclear Physics(MPIK),Heidelberg(Germany) following the dust detectors on theHEOS 2satellite anddust detectors on the Galileo and Ulysses space probesand the more complex dust analyzers on theHelios spacecraft,theGiottoandVeGa spacecrafttoHalley's Comet.The new dust analyzer system was developed by a team of scientists led byEberhard Grünand engineers led by Dietmar Linkert to analyze dust in theSaturn systemon board theCassini spacecraft.This instrument employs a larger sensitive area (0.1 m2) impact detector, a smaller time-of-flight mass spectrometer chemical analyzer and two high rate polarizedpolyvinylidene fluoride(PVDF) detectors, in order to cope with the high fluxes during crossings of the E ring. The Max Planck Institute for Nuclear Physics in Heidelberg was responsible for the overall instrument development and test. Major contributions were provided by the DLR in Berlin-Adlershof (mechanics, cleanliness, thermal design, tests),Tony McDonnellfromUniversity of Canterbury(chemical analyzer, UK),Rutherford Appleton Laboratory(spectrometer electronics, UK) and G. Pahl (mechanical design, Munich, Ger). The PVDF detectors were provided by Tony Tuzzolino from theUniversity of Chicago. The proposing Principal Investigator for CDA wasEberhard Grün.In 1990 the PI-ship was handed over to Ralf Srama from theMax Planck Institute for Nuclear Physics,who is now at theUniversity of Stuttgart,Germany. Ralf Srama got his degree “Dr.-Ing.”from theTechnical University of Munichfor his Thesis (10 Nov. 2000, in German), "From the Cosmic-Dust-Analyzer to a model describing scientific spacecraft".[2]

Cassini spacecraft with instruments

The main sensor of CDA is animpact ionizationdetector (IID) like theGalileo and Ulysses Dust Detectors.In the center of the hemispherical target is the smaller (0.016 m2) Chemical Analyzer Target, CAT, at +1000 V electric potential. Three millimeter in front of the target is a grid at 0 V potential. Dust impacts onto CAT generate a plasma that is separated by the high electric field. Ions obtain an energy of ~1000eV and are focused towards the center collector. Ions are partly collected by the semi-transparent grid at 230 millimeter distance and the centerelectron multiplier.The waveforms of the charge signals are measured, stored and transmitted to ground. The multiplier signal represents atime-of-flightmass spectrumof the released ions. Two of the four grids at the entrance of the analyzerpick-upthe electric charge of the dust particle. With these capabilities CDA can be considered a prototypedust telescope.

CDA measured the micrometeoroid environment for 18 years, from 1999 until the last active seconds of Cassini in 2017 without major degradation. The instrument fly-away-cover was released already in 1997 on day 317. Science planning and operations were managed by Max-Planck-Institute for Nuclear Physics and later by the University of Stuttgart.

The Cassini spacecraft was a three-axes stabilized spacecraft with the antenna occasionally pointing to Earth in order to download data and receive operational commands. In the mean time Cassini’s attitude was controlled by requested observations from one or more of the 12 instruments onboard. In order to obtain some more control of its pointing attitude, CDA employed a turntable between the spacecraft and the dust analyzer.

Major discoveries and observations[edit]

During interplanetary cruise[edit]

From launch in 1997 until arrival at Saturn in 2004,Cassini–Huygenscruised interplanetary space from 0.7 to 10 AU. During this time there were long periods useful for observations ofinterplanetaryandinterstellar dust[3]in the inner planetary system. Highlights were the detection of electrical charges[4]of dust in interplanetary space and the determination of the composition[5]of interplanetary dust particles. No measurements were possible during the crossing of the asteroid belt. During Jupiter flyby in 2000 there was a chance to analyze nanometer-sized dust stream particles[6]and demonstrate their compositional relation to Jupiter's moon Io where they originate from. On approach toSaturnin 2004, similar streams of submicron grains with speeds in the order of 100 km/s were detected.[7]These particles originate mostly from the outer parts of the dense rings. They were ejected by Saturn’s magnetic field until they become entrained in the solar wind magnetic field. The Saturn stream particles consist of silicate impurities of the primary icy ring particles.

In Saturn orbit[edit]

During Cassini’s 292 orbits around Saturn (2004 to 2017) CDA measured several million dust impacts that characterize dust mostly in Saturn’s E ring.[8][9]In this process CDA found that the E ring extends about twice as far from Saturn as optically observed. Measurements of variable dust charges[10]depending on the magnetospheric plasma conditions (allowed the definition of a dynamical dust model[11]of Saturn's E ring describing the observed properties. In 2005 during Cassini’s close flyby ofEnceladuswithin 175 km from the surface CDA together with two other Cassini instruments discovered active ice geysers[12]located at the south pole of Saturn's moon Enceladus. Later, detailed compositional analyses[13]of the water ice grains in the vicinity of Enceladus led to the discovery of large reservoirs of liquid water oceans[14]below the icy crust of Enceladus. During the Cassini spacecraft’sGrand Finale missionin 2017, it performed 22 traversals of the region between Saturn and its innermost D ring. During this path CDA detected of dust from Saturn's dense rings.[15]Most analyzed grains were a few tens of nanometers in size and had silicate and water-ice composition. For most of Cassini’s orbital tour CDA observed a faint signature of interstellar dust in the largely dominant foreground of E ring water-ice particles. Mass spectra of the interstellar grains suggest the presence of magnesium-rich grains of silicate and oxide composition, some with iron inclusions.[16]Major discoveries until 2011 were summarized in a dedicated paper.[17]

See also[edit]

References[edit]

  1. ^Srama, R.; Ahrens, T.J.; Altobelli, N.; Auer, S.; Bradley, J.; Burton, M.; Dikarev, V.; Economou, T.; Fechtig, H.; Görlich, M.; Grande, M.; Grün, E.; Havnes, O.; Helfert, S.; Horanyi, M.; Igenbergs, E.; Jessberger, E.; Johnson, T.V.; Kempf, S.; Krivov, A.; Krüger, H.; Mocker-Ahlreep, A.; Moragas-Klostermeyer, G.; Lamy, P.; Landgraf, M.; Linkert, D.; Linkert, G.; Lura, F.; McDonnell, J.A.M.; Möhlmann, D.; Morfill, G.; Roy, M.; Schäfer, G.; Schlotzhauer, G.; Schwehm, G.; Spahn, F.; Stübig, M.; Svestka, J.; Tschernjawski, V.; Tuzzolino, A.; Wäsch, R.; Zook, H. (September 2004)."The Cassini Cosmic Dust Analyzer".Space Science Reviews.114(1–4): 465-518.Bibcode:2004SSRv..114..465S.doi:10.1007/s11214-004-1435-z.S2CID53122588.Retrieved19 February2022.
  2. ^"Thesis Ralf Srama".Retrieved19 February2022.
  3. ^Altobelli, N.; Kempf, S.; Landgraf, M.; Srama, R.; Dikarev, V.; Krüger, H.; Moragas-Klostermeyer, G.; Grün, E. (October 2003)."Cassini between Venus and Earth: Detection of interstellar dust".Journal of Geophysical Research.108(A10): 8032.Bibcode:2003JGRA..108.8032A.doi:10.1029/2003JA009874.
  4. ^Kempf, S.; Srama, R.; Altobelli, N.; Auer, S.; Tschernjawski, V.; Bradley, J.; Burton, M.; Helfert, S.; Johnson, T.V.; Krüger, H.; Moragas-Klostermeyer, G.; Grün, E. (October 2004)."Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains".Icarus.171(2): 317-335.Bibcode:2004Icar..171..317K.doi:10.1016/j.icarus.2004.05.017.Retrieved22 February2022.
  5. ^Hillier, J.; Green, E.; McBride, N.; Altobelli, N.; Postberg, F.; Kempf, S.; Schwanenthal, J.; Srama, R.; McDonnell, J.A.M.; Grün, E. (October 2007)."Interplanetary dust detected by the Cassini CDA Chemical Analyser".Icarus.190(2): 643-654.Bibcode:2007Icar..190..643H.doi:10.1016/j.icarus.2007.03.024.Retrieved22 February2022.
  6. ^Postberg, F.; Kempf, S.; Srama, R.; Green, S.; Hillier, J-; McBride, N.; Grün, E. (July 2006)."Composition of jovian dust stream particles".Icarus.183(1): 122-134.Bibcode:2006Icar..183..122P.doi:10.1016/j.icarus.2006.02.001.Retrieved22 February2022.
  7. ^Kempf, S.; Srama, R.; Postberg, F.; Green, S.; Helfert, S.; Hillier, J.; McBride, N.; McDonnell, J.A.M.; Moragas-Klostermeyer, G.; Roy, M; Grün, E. (February 2005)."Composition of Saturnian Stream Particles".Science.307(5713): 1274–1276.Bibcode:2005Sci...307.1274K.doi:10.1126/science.1106218.PMID15731446.S2CID35810874.Retrieved25 February2022.
  8. ^Srama, R.; Kempf, S.; Moragas-Klostermeyer, G.; Helfert, S.; Ahrens, T.J.; Altobelli, N.; Auer, S.; Beckmann, U.; Bradley, J.; Burton, M.; Dikarev, V.; Economou, T.; Fechtig, H.; Green, S.; Grande, M.; Havnes, O.; Hillier, J.; Horanyi, M.; Igenbergs, E.; Jessberger, E.; Johnson, T.V.; Krüger, H.; Matt, G.; McBride, N.; Mocker, A.; Lamy, P.; Linkert, D.; Linkert, G.; Lura, F.; McDonnell, J.A.M.; Möhlmann, D.; Morfill, G.; Postberg, F.; Roy, M.; Schwehm, G.; Spahn, F.; Svestka, J.; Tschernjawski, V.; Tuzzolino, A.; Wäsch, R.; Grün, E. (August 2006)."In situ dust measurements in the inner Saturnian system".Planetary and Space Science.54(9–10): 967-987.Bibcode:2006P&SS...54..967S.doi:10.1016/j.pss.2006.05.021.Retrieved25 February2022.
  9. ^Hillier, J.; Green, S.F.; McBride, N.; Schwanenthal, J.; Postberg, F.; Srama, R.; Kempf, S.; Moragas-Klostermeyer, G.; McDonnell, J.A.M.; Grün, E. (June 2007)."The composition of Saturn's E ring".Monthly Notices of the Royal Astronomical Society.377(4): 1588-1596.Bibcode:2007MNRAS.377.1588H.doi:10.1111/j.1365-2966.2007.11710.x.S2CID124773731.Retrieved25 February2022.
  10. ^Kempf, S.; Beckmann, U.; Srama, R.; Horanyi, M.; Auer, S.; Grün, E. (August 2006)."The electrostatic potential of E ring particles".Planetary and Space Science.54(9–10): 999-1006.Bibcode:2006P&SS...54..999K.doi:10.1016/j.pss.2006.05.012.Retrieved25 February2022.
  11. ^Horanyi, M.; Juhasz, A.; Morfill, G.E. (February 2008)."Large-scale structure of Saturn's E-ring".Geophysical Research Letters.35(4): L04203.Bibcode:2008GeoRL..35.4203H.doi:10.1029/2007GL032726.S2CID129314362.
  12. ^Spahn, F.; Schmidt, J.; Albers, N.; Hörning, M.; Makuch, M.; Seiß, M.; Kempf, S.; Srama, R.; Dikarev, V.; Helfert, S.; Moragasd-Klostermeyer, G.; Krivov, A.; Sremcevic, M.; Tuzzolono, A.; Economou, T.; Grün, E. (March 2006)."Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring".Science.311(5766): 1416–1418.Bibcode:2006Sci...311.1416S.CiteSeerX10.1.1.466.6748.doi:10.1126/science.1121375.PMID16527969.S2CID33554377.Retrieved25 February2022.
  13. ^Postberg, F.; Kempf, S.; Hillier, J.; Srama, R.; Green, S.; McBride, N.; Grün, E. (February 2008)."The E-ring in the vicinity of Enceladus. II. Probing the moon's interior—The composition of E-ring particles".Icarus.193(2): 438-454.Bibcode:2008Icar..193..438P.doi:10.1016/j.icarus.2007.09.001.Retrieved25 February2022.
  14. ^Postberg, F.; Schmidt, J.; Hillier, J.; Kempf, S.; Srama, R. (June 2011)."A salt-water reservoir as the source of a compositionally stratified plume on Enceladus".Nature.474(7353): 620–622.Bibcode:2011Natur.474..620P.doi:10.1038/nature10175.PMID21697830.S2CID4400807.Retrieved25 February2022.
  15. ^Hsu, H.W.; Schmidt, J.; Kempf, S.; Postberg, F.; Moragas-Klostermeyer, G.; Seiß, M.; Hoffmann, H.; Burton, M.; Ye, S.Y.; Kurth, W.; Horanyi, M.; Khawaja, N.; Spahn, F.; Schirdewahn, D.; O'Donoghue, J.; Moore, L.; Cuzzi, J.; Jones, G-; Srama, R. (October 2018)."In situ collection of dust grains falling from Saturn's rings into its atmosphere"(PDF).Science.362(6410).Bibcode:2018Sci...362.3185H.doi:10.1126/science.aat3185.PMID30287635.S2CID52920453.
  16. ^Altobelli, N.; Postberg, F.; Fiege, K.; Trieloff, M.; Kimura, H.; Sterken, V.; Hsu, W.H.; Hillier, J.; Khawaja, N.; Moragas-Klostermeyer, G.; Blum, J.; Burton, M.; Srama, R.; Kempf, S.; Grün, E. (April 2016)."Flux and composition of interstellar dust at Saturn from Cassini's Cosmic Dust Analyzer".Science.352(6283): 312–318.Bibcode:2016Sci...352..312A.doi:10.1126/science.aac6397.PMID27081064.S2CID24111692.Retrieved26 February2022.
  17. ^Srama, R.; Kempf, S.; Moragas-Klostermeyer, G.; Altobelli, N.; Auer, S.; Beckmann, U.; Bugiel, S.; Burton, M.; Economomou, T.; Fechtig, H.; Fiege, K. (2011)."The cosmic dust analyser onboard cassini: ten years of discoveries".CEAS Space Journal.2(1–4): 3–16.arXiv:1802.04772.Bibcode:2011CEAS....2....3S.doi:10.1007/s12567-011-0014-x.ISSN1868-2502.S2CID15586830.
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