uu.seUppsala University Publications
Change search
Refine search result
12 1 - 50 of 67
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Arridge, Christopher S.
    et al.
    Agnor, Craig B.
    Andre, Nicolas
    Baines, Kevin H.
    Fletcher, Leigh N.
    Gautier, Daniel
    Hofstadter, Mark D.
    Jones, Geraint H.
    Lamy, Laurent
    Langevin, Yves
    Mousis, Olivier
    Nettelmann, Nadine
    Russell, Christopher T.
    Stallard, Tom
    Tiscareno, Matthew S.
    Tobie, Gabriel
    Bacon, Andrew
    Chaloner, Chris
    Guest, Michael
    Kemble, Steve
    Peacocke, Lisa
    Achilleos, Nicholas
    Andert, Thomas P.
    Banfield, Don
    Barabash, Stas
    Barthelemy, Mathieu
    Bertucci, Cesar
    Brandt, Pontus
    Cecconi, Baptiste
    Chakrabarti, Supriya
    Cheng, Andy F.
    Christensen, Ulrich
    Christou, Apostolos
    Coates, Andrew J.
    Collinson, Glyn
    Cooper, John F.
    Courtin, Regis
    Dougherty, Michele K.
    Ebert, Robert W.
    Entradas, Marta
    Fazakerley, Andrew N.
    Fortney, Jonathan J.
    Galand, Marina
    Gustin, Jaques
    Hedman, Matthew
    Helled, Ravit
    Henri, Pierre
    Hess, Sebastien
    Holme, Richard
    Karatekin, Ozgur
    Krupp, Norbert
    Leisner, Jared
    Martin-Torres, Javier
    Masters, Adam
    Melin, Henrik
    Miller, Steve
    Mueller-Wodarg, Ingo
    Noyelles, Benoit
    Paranicas, Chris
    de Pater, Imke
    Paetzold, Martin
    Prange, Renee
    Quemerais, Eric
    Roussos, Elias
    Rymer, Abigail M.
    Sanchez-Lavega, Agustin
    Saur, Joachim
    Sayanagi, Kunio M.
    Schenk, Paul
    Schubert, Gerald
    Sergis, Nick
    Sohl, Frank
    Sittler, Edward C., Jr.
    Teanby, Nick A.
    Tellmann, Silvia
    Turtle, Elizabeth P.
    Vinatier, Sandrine
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Zarka, Philippe
    Uranus Pathfinder: exploring the origins and evolution of Ice Giant planets2012In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 33, no 2-3, p. 753-791Article in journal (Refereed)
    Abstract [en]

    The "Ice Giants" Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA's Cosmic Vision 2015-2025. UP was proposed to the European Space Agency's M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines the need to develop power sources suitable for the outer Solar System. The UP science case is based around exploring the origins, evolution, and processes at work in Ice Giant planetary systems. Three broad themes were identified: (1) Uranus as an Ice Giant, (2) An Ice Giant planetary system, and (3) An asymmetric magnetosphere. Due to the long interplanetary transfer from Earth to Uranus a significant cruise-phase science theme was also developed. The UP mission concept calls for the use of a Mars Express/Rosetta-type platform to launch on a Soyuz-Fregat in 2021 and entering into an eccentric polar orbit around Uranus in the 2036-2037 timeframe. The science payload has a strong heritage in Europe and beyond and requires no significant technology developments.

  • 2.
    Buchert, Stephan C.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gill, Reine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Åhlén, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Knudsen, David
    Univ Calgary, Calgary, AB, Canada..
    Burchill, Johnathan
    Univ Calgary, Calgary, AB, Canada..
    Archer, William
    Univ Calgary, Calgary, AB, Canada..
    Kouznetsov, Alexei
    Univ Calgary, Calgary, AB, Canada..
    Stricker, Nico
    ESA ESTEC, Noordwijk, Netherlands..
    Bouridah, Abderrazak
    ESA ESTEC, Noordwijk, Netherlands..
    Bock, Ralph
    ESA ESTEC, Noordwijk, Netherlands..
    Haggstrom, Ingemar
    EISCAT Sci Assoc, Headquarters, Kiruna, Sweden..
    Rietveld, Michael
    EISCAT Sci Assoc, Tromso, Norway..
    Gonzalez, Sixto
    Natl Astron & Ionosphere Ctr, Arecibo, PR USA..
    Aponte, Nestor
    Natl Astron & Ionosphere Ctr, Arecibo, PR USA..
    First results from the Langmuir probes on the Swarm satellites2014In: 2014 XXXITH URSI General Assembly And Scientific Symposium (URSI GASS), 2014Conference paper (Refereed)
  • 3.
    Buchert, Stephan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Zangerl, Franz
    Sust, Manfred
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Opgenoorth, Hermann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    SWARM observations of equatorial electron densities and topside GPS track losses2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 7, p. 2088-2092Article in journal (Refereed)
    Abstract [en]

    The SWARM satellites have both upward looking GPS receivers and Langmuir probes. The receivers repeatedly lost track of the L1 band signal in January-February 2014 at postsunset hours, when SWARM was at nearly 500km altitude. This indicates that the signal was disturbed by ionospheric irregularities at this height and above. The track losses occurred right at density gradients associated with equatorial plasma bubbles and predominantly where the measured background density was highest. The signal showed strong phase scintillations rather than in amplitude, indicating that SWARM might be in the near field of an ionospheric phase screen. Density biteouts, depletions between steep gradients, were up to almost 3 orders of magnitude deep in the background of a more shallow trough centered at the magnetic equator. Comparison between satellites shows that the biteout structure strongly varied in longitude over approximate to 100km and has in north-south steep walls.

  • 4. Coates, A. J.
    et al.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cui, J.
    Wellbrock, A.
    Szego, K.
    Recent Results from Titan's Ionosphere2011In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 162, no 1-4, p. 85-111Article, review/survey (Refereed)
    Abstract [en]

    Titan has the most significant atmosphere of any moon in the solar system, with a pressure at the surface larger than the Earth's. It also has a significant ionosphere, which is usually immersed in Saturn's magnetosphere. Occasionally it exits into Saturn's magnetosheath. In this paper we review several recent advances in our understanding of Titan's ionosphere, and present some comparisons with the other unmagnetized objects Mars and Venus. We present aspects of the ionospheric structure, chemistry, electrodynamic coupling and transport processes. We also review observations of ionospheric photoelectrons at Titan, Mars and Venus. Where appropriate, we mention the effects on ionospheric escape.

  • 5.
    Cravens, T. E.
    et al.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perry, M.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    The Ion Composition of Saturn's Equatorial Ionosphere as Observed by Cassini2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6315-6321Article in journal (Refereed)
    Abstract [en]

    The Cassini Orbiter made the first in situ measurements of the upper atmosphere and ionosphere of Saturn in 2017. The Ion and Neutral Mass Spectrometer (INMS) found molecular hydrogen and helium as well as minor species including water, methane, ammonia, and organics. INMS ion mode measurements of light ion species (H+, H-2(+), H-3(+), and He+) and Radio and Plasma Wave Science instrument measurements of electron densities are presented. A photochemical analysis of the INMS and Radio and Plasma Wave Science data indicates that the major ion species near the ionospheric peak must be heavy and molecular with a short chemical lifetime. A quantitative explanation of measured H+ and H-3(+) densities requires that they chemically react with one or more heavy neutral molecular species that have mixing ratios of about 100 ppm.

  • 6.
    Cravens, T. E.
    et al.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Renzaglia, A.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perry, M.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Plasma Transport in Saturn's Low-Latitude Ionosphere: Cassini Data2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 6, p. 4881-4888Article in journal (Refereed)
    Abstract [en]

    In 2017 the Cassini Orbiter made the first in situ measurements of the upper atmosphere and ionosphere of Saturn. The Ion and Neutral Mass Spectrometer in its ion mode measured densities of light ion species (H+, H-2(+), H-3(+), and He+), and the Radio and Plasma Wave Science instrument measured electron densities. During proximal orbit 287 (denoted P287), Cassini reached down to an altitude of about 3,000 km above the 1 bar atmospheric pressure level. The topside ionosphere plasma densities measured for P287 were consistent with ionospheric measurements during other proximal orbits. Spacecraft potentials were measured by the Radio and Plasma Wave Science Langmuir probe and are typically about negative 0.3 V. Also, for this one orbit, Ion and Neutral Mass Spectrometer was operated in an instrument mode allowing the energies of incident H+ ions to be measured. H+ is the major ion species in the topside ionosphere. Ion flow speeds relative to Saturn's atmosphere were determined. In the southern hemisphere, including near closest approach, the measured ion speeds were close to zero relative to Saturn's corotating atmosphere, but for northern latitudes, southward ion flow of about 3 km/s was observed. One possible interpretation is that the ring shadowing of the southern hemisphere sets up an interhemispheric plasma pressure gradient driving this flow.

  • 7.
    Desai, R. T.
    et al.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, Gower St, London WC1E 6BT, England..
    Coates, A. J.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, Gower St, London WC1E 6BT, England..
    Wellbrock, A.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, Gower St, London WC1E 6BT, England..
    Vuitton, V.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France..
    Crary, F. J.
    Univ Colorado, Lab Atmospher & Space Phys, Innovat Dr, Boulder, CO 80303 USA..
    Gonzalez-Caniulef, D.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England..
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Jones, G. H.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, Gower St, London WC1E 6BT, England..
    Lewis, G. R.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England..
    Waite, J. H.
    Southwest Res Inst SWRI, Space Sci & Engn Div, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Cordiner, M.
    NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA..
    Taylor, S. A.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, Gower St, London WC1E 6BT, England..
    Kataria, D. O.
    Univ Coll London, Mullard Space Sci Lab, Holmbury RH5 6NT, Surrey, England..
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sittler, E. C.
    NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA..
    Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan's Ionosphere2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 844, no 2, article id L18Article in journal (Refereed)
    Abstract [en]

    Cassini discovered a plethora of neutral and ionized molecules in Titan's ionosphere including, surprisingly, anions and negatively charged molecules extending up to 13,800 u q-1. In this Letter, we forward model the Cassini electron spectrometer response function to this unexpected ionospheric component to achieve an increased mass resolving capability for negatively charged species observed at Titan altitudes of 950-1300 km. We report on detections consistently centered between 25.8 and 26.0 u q-1 and between 49.0-50.1 u q(-1) which are identified as belonging to the carbon chain anions, CN-/C3N- and/or C2H-/C4H-, in agreement with chemical model predictions. At higher ionospheric altitudes, detections at 73-74 u q-1 could be attributed to the further carbon chain anions C5N-/C6H- but at lower altitudes and during further encounters extend over a higher mass/charge range. This, as well as further intermediary anions detected at > 100 u, provide the first evidence for efficient anion chemistry in space involving structures other than linear chains. Furthermore, at altitudes below < 1100 km, the low-mass anions (< 150 u q-1) were found to deplete at a rate proportional to the growth of the larger molecules, a correlation that indicates the anions are tightly coupled to the growth process. This study adds Titan to an increasing list of astrophysical environments where chain anions have been observed and shows that anion chemistry plays a role in the formation of complex organics within a planetary atmosphere as well as in the interstellar medium.

  • 8.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Bertucci, C.
    IAFE, Buenos Aires, DF, Argentina..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Holmberg, Mika K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Jackman, C. M.
    Univ Southampton, Southampton, Hants, England..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Menietti, J. D.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Effects of Saturn's magnetospheric dynamics on Titan's ionosphere2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 10, p. 8884-8898Article in journal (Refereed)
    Abstract [en]

    We use the Cassini Radio and Plasma Wave Science/Langmuir probe measurements of the electron density from the first 110 flybys of Titan to study how Saturn's magnetosphere influences Titan's ionosphere. The data is first corrected for biased sampling due to varying solar zenith angle and solar energy flux (solar cycle effects). We then present results showing that the electron density in Titan's ionosphere, in the altitude range 1600-2400km, is increased by about a factor of 2.5 when Titan is located on the nightside of Saturn (Saturn local time (SLT) 21-03h) compared to when on the dayside (SLT 09-15 h). For lower altitudes (1100-1600km) the main dividing factor for the ionospheric density is the ambient magnetospheric conditions. When Titan is located in the magnetospheric current sheet, the electron density in Titan's ionosphere is about a factor of 1.4 higher compared to when Titan is located in the magnetospheric lobes. The factor of 1.4 increase in between sheet and lobe flybys is interpreted as an effect of increased particle impact ionization from approximate to 200eV sheet electrons. The factor of 2.5 increase in electron density between flybys on Saturn's nightside and dayside is suggested to be an effect of the pressure balance between thermal plus magnetic pressure in Titan's ionosphere against the dynamic pressure and energetic particle pressure in Saturn's magnetosphere.

  • 9.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Ågren, K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cravens, T. E.
    Girazian, Z.
    Solar cycle modulation of Titan's ionosphere2013In: Journal of Geophysical Research-Space Physics, ISSN 2169-9380, Vol. 118, no 8, p. 5255-5264Article in journal (Refereed)
    Abstract [en]

    During the six Cassini Titan flybys T83-T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15-30%, compared to previous average. These measurements suggest that a longterm change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83-T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle N-norm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16-T71). The integrated solar irradiance over the wavelengths 1-80nm, i.e., the solar energy flux, F-e, correlates well with the observed ionospheric peak density values. Chapman layer theory predicts that Nnorm<mml:msubsup>Fek</mml:msubsup>, with k=0.5. We find observationally that the exponent k=0.540.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500cm(-3), i.e., 85-160% more than has been measured during the entire Cassini mission.

  • 10.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Roussos, E.
    Garnier, P.
    Cravens, T. E.
    Badman, S. V.
    Modolo, R.
    Bertucci, C.
    Dougherty, M. K.
    Extreme densities in Titan's ionosphere during the T85 magnetosheath encounter2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 12, p. 2879-2883Article in journal (Refereed)
    Abstract [en]

    We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310cm(-3) during the T85 Titan flyby. This is at least 500cm(-3) higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons.

  • 11.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Lebreton, J. -P
    Gasc, S.
    Rubin, M.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gill, Reine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Erik P. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Carr, C. M.
    Cupido, E.
    Glassmeier, K. -H
    Goldstein, R.
    Koenders, C.
    Mandt, K.
    Nemeth, Z.
    Nilsson, H.
    Richter, I.
    Wieser, G. Stenberg
    Szego, K.
    Volwerk, M.
    Spatial distribution of low-energy plasma around comet 67P/CG from Rosetta measurements2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 11, p. 4263-4269Article in journal (Refereed)
    Abstract [en]

    We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be approximate to 1-210(-6), at a cometocentric distance of 10km and at 3.1AU from the Sun. A clear 6.2h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260km from the nucleus falls off with radial distance as approximate to 1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet.

  • 12.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Snowden, D.
    Cent Washington Univ, Dept Phys, Ellensburg, WA USA.
    Regoli, L. H.
    Univ Michigan, Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Imperial Coll London, Dept Phys, London, England.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Bertucci, C.
    IAFE, Ciudad Univ, Buenos Aires, DF, Argentina.
    Cui, J.
    Sun Yat Sen Univ, Sch Atmospher Sci, Zhuhai, Peoples R China;Chinese Acad Sci, Key Lab Lunar & Deep Space Explorat, Beijing, Peoples R China.
    Titan's Variable Ionosphere During the T118 and T119 Cassini Flybys2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 17, p. 8721-8728Article in journal (Refereed)
    Abstract [en]

    We report on unusual dynamics in Titan's ionosphere as a significant difference in ionospheric electron density is observed between the T118 and T119 Cassini nightside flybys. Two distinct nightside electron density peaks were present during T118, at 1,150 and 1,200km, and the lowest density ever observed in Titan's ionosphere at altitudes 1,000-1,350km was during T118. These flybys were quite similar in geometry, Saturn local time, neutral density, extreme ultraviolet flux, and ambient magnetic field conditions. Despite this, the Radio and Plasma Waves/Langmuir Probe measured a density difference up to a factor of 6 between the passes. The overall difference was present and similar during both inbound and outbound legs. By ruling out other factors, we suggest that an exceptionally low rate of particle impact ionization in combination with dynamics in the ionosphere is the explanation for the observations. Plain Language Summary Using the Cassini satellite in orbit around Saturn, we make measurements during two close passes of the moon Titan. We observe how the electron density in the uppermost part of the moon's atmosphere-the ionosphere-changes drastically from one pass to the next. We also observe unexpectedly high peaks of electron density in a specific altitude range during the first pass. The findings are attributed to low influx of charged particles from Saturn's magnetosphere as well as to increased dynamics of the plasma in the ionosphere. The study emphasizes the complexity of the physical process at play at the moon and aims at gaining further understanding of this environment.

  • 13.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko W.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, D. J.
    Cowley, S. W. H.
    Wellbrock, A.
    Coates, A. J.
    Bertucci, C.
    Dougherty, M. K.
    Structured ionospheric outflow during the Cassini T55-T59 Titan flybys2011In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 59, no 8, p. 788-797Article in journal (Refereed)
    Abstract [en]

    During the final three of the five consecutive and similar Cassini Titan flybys T55-T59 we observe a region characterized by high plasma densities (electron densities of 1-8 cm(-3)) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. The ions in this plasma plume are moving in the direction away from Titan and are a mixture of both light and heavy ions with composition revealing that their origin are in Titan's ionosphere, while the electrons are more isotropically distributed. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanisms behind this outflow, and suggest that it could be caused by ambipolar diffusion, magnetic moment pumping or dispersive Alfven waves.

  • 14.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Wahlund, Jan -Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders. I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ye, S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Morooka, M. W.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Dougherty, M. K.
    Univ London Imperial Coll Sci Technol & Med, Blackett Lab, London SW7 2BZ, England..
    Plasma regions, charged dust and field-aligned currents near Enceladus2015In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 117, p. 453-469Article in journal (Refereed)
    Abstract [en]

    We use data from several instruments on board Cassini to determine the characteristics of the plasma and dust regions around Saturn's moon Enceladus. For this we utilize the Langmuir probe and the electric antenna connected to the wideband receiver of the radio and plasma wave science (RPWS) instrument package as well as the magnetometer (MAG). We show that there are several distinct plasma and dust regions around Enceladus. Specifically they are the plume filled with neutral gas, plasma, and charged dust, with a distinct edge boundary region. Here we present observations of a new distinct plasma region, being a dust trail on the downstream side. This is seen both as a difference in ion and electron densities, indicating the presence of charged dust, and directly from the signals created on RPWS antennas by the dust impacts on the spacecraft. Furthermore, we show a very good scaling of these two independent dust density measurement methods over four orders of magnitude in dust density, thereby for the first time cross-validating them. To establish equilibrium with the surrounding plasma the dust becomes negatively charged by attracting free electrons. The dust distribution follows a simple power law and the smallest dust particles in the dust trail region are found to be 10 nm in size as well as in the edge region around the plume. Inside the plume the presence of even smaller particles of about 1 nm is inferred. From the magnetic field measurements we infer strong field-aligned currents at the geometrical edge of Enceladus.

  • 15.
    Eriksson, Anders I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Engelhardt, Ilka. A. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Boström, Rolf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    LPC2E, Lab Phys & Chim Environm & Espace.
    Lebreton, J. -P
    LPC2E, Lab Phys & Chim Environm & Espace.
    Miloch, W. J.
    Univ Oslo, Dept Phys.
    Paulsson, J. J. P.
    Univ Oslo, Dept Phys.
    Wedlund, Cyril Simon
    Univ Oslo, Dept Phys.
    Yang, L.
    Univ Oslo, Dept Phys.
    Karlsson, T.
    Royal Inst Technol, Alfvén Lab.
    Jarvinen, R.
    Finnish Meteorol Inst, Helsinki 00560.
    Broiles, Thomas
    Southwest Res Inst, San Antonio.
    Mandt, K.
    Southwest Res Inst, San Antonio; Univ Texas San Antonio, Dept Phys & Astron.
    Carr, C. M.
    Imperial Coll London, Dept Phys.
    Galand, M.
    Imperial Coll London, Dept Phys.
    Nilsson, H.
    Swedish Inst Space Phys, S-98128 Kiruna.
    Norberg, C.
    Swedish Inst Space Phys, S-98128 Kiruna.
    Cold and warm electrons at comet 67P/Churyumov-Gerasimenko2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A15Article in journal (Refereed)
    Abstract [en]

    Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma.

    Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas.

    Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V.

    Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

  • 16.
    Farrell, W. M.
    et al.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    MacDowall, R. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Sulaiman, A. H.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Saturn's Plasma Density Depletions Along Magnetic Field Lines Connected to the Main Rings2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16, p. 8104-8110Article in journal (Refereed)
    Abstract [en]

    We report on a set of clear and abrupt decreases in the high-frequency boundary of whistler mode emissions detected by Cassini at high latitudes (about +/- 40 degrees) during the low-altitude proximal flybys of Saturn. These abrupt decreases or dropouts have start and stop locations that correspond to L shells at the edges of the A and B rings. Langmuir probe measurements can confirm, in some cases, that the abrupt decrease in the high-frequency whistler mode boundary is associated with a corresponding abrupt electron density dropout over evacuated field lines connected to the A and B rings. Wideband data also reveal electron plasma oscillations and whistler mode cutoffs consistent with a low-density plasma in the region. The observation of the electron density dropout along ring-connecting field lines suggests that strong ambipolar forces are operating, drawing cold ionospheric ions outward to fill the flux tubes. There is an analog with the refilling of flux tubes in the terrestrial plasmasphere. We suggest that the ring-connected electron density dropouts observed between 1.1 and 1.3 R-s are connected to the low-density ring plasma cavity observed overtop the A and B rings during the 2004 Saturn orbital insertion pass.

    Plain Language Summary We present Cassini observations during the close passes by the planet Saturn indicating that plasma on magnetic field lines that pass through the A and B rings is of anomalously low density. These observations are consistent with the Saturn orbit insertion observations of a plasma cavity located at equatorial regions overtop the dense B ring. Using a terrestrial analogy, we suggest that the low-density conditions overtop the rings create an electrical force, called an ambipolar electric field that draws plasma out of the ionosphere in an attempt to replenish the plasma void found at equatorial regions.

  • 17. Farrell, W. M.
    et al.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Gurnett, D. A.
    Kurth, W. S.
    MacDowall, R. J.
    An estimate of the dust pickup current at Enceladus2014In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 239, p. 217-221Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the acceleration of submicron dust originating at Enceladus by a reduced co-rotating E-field is capable of creating a dust pickup current perpendicular to the magnetic field with values ranging from 3 to 15 kA (depending upon the effective grain charge). Such a current represents a new contribution to the total pickup current in the region. As such, we suggest that dust pickup currents, along with ion and electron pickup currents, are all active within the plume.

  • 18.
    Farrell, W. M.
    et al.
    NASA Goddard Space Flight Ctr, Solar Syst Explorat Div, Greenbelt, MD 20771 USA..
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    MacDowall, R. J.
    NASA Goddard Space Flight Ctr, Solar Syst Explorat Div, Greenbelt, MD 20771 USA..
    Ion trapping by dust grains: Simulation applications to the Enceladus plume2017In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 122, no 4, p. 729-743Article in journal (Refereed)
    Abstract [en]

    Using a particle-in-cell electrostatic simulation, we examine the conditions that allow low-energy ions, like those produced in the Enceladus plume, to be attracted and trapped within the sheaths of negatively charged dust grains. The conventional wisdom is that all new ions produced in the Enceladus plume are free to get picked up (i.e., accelerated by the local E field to then undergo vB acceleration). However, we suggest herein that the presence of submicron-charged dust in the plume impedes this pickup process since the local grain electric field greatly exceeds the corotation E fields. The simulations demonstrate that cold ions will tend to accelerate toward the negatively charged grains and become part of the ion plasma sheath. These trapped ions will move with the grains, exiting the plume region at the dust speed. We suggest that Cassini's Langmuir probe is measuring the entire ion population (free and trapped ions), while the Cassini magnetometer detects the magnetic perturbations associated with pickup currents from the smaller population of free ions, with this distinction possibly reconciling the ongoing debate in the literature on the ion density in the plume.

  • 19. Farrell, William M.
    et al.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gurnett, Donald A.
    Kurth, William S.
    MacDowall, Robert J.
    The electromagnetic pickup of submicron-sized dust above Enceladus's northern hemisphere2012In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 219, no 1, p. 498-501Article in journal (Refereed)
    Abstract [en]

    As the saturnian magnetoplasma sweeps past Enceladus, it experiences both a decrease in electron content and sharp slowdown in the northern hemisphere region within similar to 5 Enceladus Radii (R-e). This slowdown is observed by Cassini in regions not obviously associated with the southern directed plume-originating ions. We suggest herein that the decrease in northern hemisphere electron content and plasma slowdown could both be related to the presence of fine dust grains that are being accelerated by the Lorentz force created within the saturnian magnetic field system.

  • 20.
    Futaana, Yoshifumi
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Barabash, Stas
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Wurz, Peter
    Univ Bern, Bern, Switzerland.
    Hurley, Dana
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Horanyi, Mihaly
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Mall, Urs
    Max Planck Inst Solar Syst Res, Gottingen, Germany.
    Andre, Nicolas
    Univ Toulouse, CNRS, IRAP, Toulouse, France.
    Ivchenko, Nickolay
    KTH Royal Inst Technol, Stockholm, Sweden.
    Oberst, Juergen
    German Aerosp Ctr, Berlin, Germany.
    Retherford, Kurt
    Southwest Res Inst, San Antonio, TX USA.
    Coates, Andrew
    UCL, Mullard Space Sci Lab, London, England.
    Masters, Adam
    Imperial Coll London, London, England.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Kallio, Esa
    Aalto Univ, Helsinki, Finland.
    SELMA mission: How do airless bodies interact with space environment? The Moon as an accessible laboratory2018In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 156, p. 23-40Article in journal (Refereed)
    Abstract [en]

    The Moon is an archetypal atmosphere-less celestial body in the Solar System. For such bodies, the environments are characterized by complex interaction among the space plasma, tenuous neutral gas, dust and the outermost layer of the surface. Here we propose the SELMA mission (Surface, Environment, and Lunar Magnetic Anomalies) to study how airless bodies interact with space environment. SELMA uses a unique combination of remote sensing via ultraviolet and infrared wavelengths, and energetic neutral atom imaging, as well as in situ measurements of exospheric gas, plasma, and dust at the Moon. After observations in a lunar orbit for one year, SELMA will conduct an impact experiment to investigate volatile content in the soil of the permanently shadowed area of the Shackleton crater. SELMA also carries an impact probe to sound the Reiner-Gamma mini-magnetosphere and its interaction with the lunar regolith from the SELMA orbit down to the surface. SELMA was proposed to the European Space Agency as a medium-class mission (M5) in October 2016. Research on the SELMA scientific themes is of importance for fundamental planetary sciences and for our general understanding of how the Solar System works. In addition, SELMA outcomes will contribute to future lunar explorations through qualitative characterization of the lunar environment and, in particular, investigation of the presence of water in the lunar soil, as a valuable resource to harvest from the lunar regolith.

  • 21.
    Futaana, Yoshifumi
    et al.
    Swedish Inst Space Phys, SE-98128 Kiruna, Sweden.
    Wang, Xiao-Dong
    Swedish Inst Space Phys, Solar Syst Phys & Space Technol Grp, SE-98128 Kiruna, Sweden.
    Roussos, Elias
    Max Planck Inst Solar Syst Res, D-37077 Gottingen, Germany.
    Krupp, Norbert
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fränz, Markus
    Barabash, Stas
    Swedish Inst Space Phys, SE-98128 Kiruna, Sweden.
    Lei, Fan
    RadMod Res Ltd, Camberley GU15 2PD, England.
    Heynderickx, Daniel
    DH Consultancy BVBA, B-3000 Leuven, Belgium.
    Truscott, Pete
    Kallisto Consultancy Ltd, Farnborough GU14 9AJ, Hants, England.
    Cipriani, Fabrice
    European Space Agcy, European Space Res & Technol Ctr, NL-2200 AG Noordwijk, Netherlands.
    Rodgers, David
    European Space Agcy, European Space Res & Technol Ctr, NL-2200 AG Noordwijk, Netherlands.
    Corotation Plasma Environment Model: An Empirical Probability Model of the Jovian Magnetosphere2018In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 46, no 6, p. 2126-2145Article in journal (Refereed)
    Abstract [en]

    We developed a new empirical model for corotating plasma in the Jovian magnetosphere. The model, named the corotation plasma environment model version 2 (CPEMv2), considers the charge density, velocity vector, and ion temperature based on Galileo/plasma system (PLS) ion data. In addition, we develop hot electron temperature and density models based on Galileo/PLS electron data. All of the models provide respective quantities in the magnetic equator plane of 9-30RJ, while the charge density model can be extended to 3-D space. A characteristic feature of the CPEM is its support of the percentile as a user input. This feature enables us to model extreme conditions in addition to normal states. In this paper, we review the foundations of the new empirical model, present a general derivation algorithm, and offer a detailed formulation of each parameter of the CPEMv2. As all CPEM parameters are of the analytical form, their implementation is straightforward, and execution involves the use of a small number of computational resources. The CPEM is flexible; for example, it can be extended, as new data (from observations or simulation results) become available. The CPEM can be used for the mission operation of the European Space Agency's mission to Jupiter, JUpiter ICy moons Explorer (JUICE), and for future data analyses.

  • 22. Garnier, P.
    et al.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, Madeleine K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Morooka, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Grimald, S.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Schippers, P.
    Gurnett, D. A.
    Krimigis, S. M.
    Krupp, N.
    Coates, A.
    Crary, F.
    Gustafsson, Georg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The detection of energetic electrons with the Cassini Langmuir probe at Saturn2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. A10202-Article in journal (Refereed)
    Abstract [en]

    The Cassini Langmuir probe, part of the Radio and Plasma Wave Science (RPWS) instrument, has provided a wealth of information about the cold and dense plasma in the Saturnian system. The analysis of the ion side current (current for negative potentials) measured by the probe from 2005 to 2008 reveals also a strong sensitivity to energetic electrons (250-450 eV). These electrons impact the surface of the probe, and generate a detectable current of secondary electrons. A broad secondary electrons current region is inferred from the observations in the dipole L Shell range of similar to 6-10, with a peak full width at half maximum (FWHM) at L = 6.4-9.4 (near the Dione and Rhea magnetic dipole L Shell values). This magnetospheric flux tube region, which displays a large day/night asymmetry, is related to the similar structure in the energetic electron fluxes as the one measured by the onboard Electron Spectrometer (ELS) of the Cassini Plasma Spectrometer (CAPS). It corresponds spatially to both the outer electron radiation belt observed by the Magnetosphere Imaging Instrument (MIMI) at high energies and to the low-energy peak which has been observed since the Voyager era. Finally, a case study suggests that the mapping of the current measured by the Langmuir probe for negative potentials can allow to identify the plasmapause-like boundary recently identified at Saturn, and thus potentially identify the separation between the closed and open magnetic field lines regions.

  • 23.
    Garnier, Philippe
    et al.
    Institut de Recherche en Astrophysique et Planétologie (IRAP).
    Holmberg, Mika
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lewis, G R
    Grimald, S Rochel
    Thomsen, M F
    Gurnetti, D A
    Coates, A J
    Crary, F J
    Dandouras, I
    The influence of the secondary electrons induced by energetic electrons impacting the Cassini Langmuir probe at Saturn2013In: Journal of geophysical research Space Physics, ISSN 2169-9402, Vol. 118, no 11, p. 7054-7073Article in journal (Refereed)
    Abstract [en]

    The Cassini Langmuir Probe (LP) onboard the Radio and Plasma Wave Science experiment has provided much information about the Saturnian cold plasma environment since the Saturn Orbit Insertion in 2004. A recent analysis revealed that the LP is also sensitive to the energetic electrons (250–450 eV) for negative potentials. These electrons impact the surface of the probe and generate a current of secondary electrons, inducing an energetic contribution to the DC level of the current-voltage (I-V) curve measured by the LP. In this paper, we further investigated this influence of the energetic electrons and (1) showed how the secondary electrons impact not only the DC level but also the slope of the (I-V) curve with unexpected positive values of the slope, (2) explained how the slope of the (I-V) curve can be used to identify where the influence of the energetic electrons is strong, (3) showed that this influence may be interpreted in terms of the critical and anticritical temperatures concept detailed by Lai and Tautz (2008), thus providing the first observational evidence for the existence of the anticritical temperature, (4) derived estimations of the maximum secondary yield value for the LP surface without using laboratory measurements, and (5) showed how to model the energetic contributions to the DC level and slope of the (I-V) curve via several methods (empirically and theoretically). This work will allow, for the whole Cassini mission, to clean the measurements influenced by such electrons. Furthermore, the understanding of this influence may be used for other missions using Langmuir probes, such as the future missions Jupiter Icy Moons Explorer at Jupiter, BepiColombo at Mercury, Rosetta at the comet Churyumov-Gerasimenko, and even the probes onboard spacecrafts in the Earth magnetosphere.

  • 24. Ghail, Richard C.
    et al.
    Wilson, Colin
    Galand, Marina
    Hall, David
    Cochrane, Chris
    Mason, Philippa
    Helbert, Joern
    MontMessin, Franck
    Limaye, Sanjay
    Patel, Manish
    Bowles, Neil
    Stam, Daphne
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Rocca, Fabio
    Waltham, David
    Mather, Tamsin A.
    Biggs, Juliet
    Genge, Matthew
    Paillou, Philippe
    Mitchell, Karl
    Wilson, Lionel
    Singh, Upendra N.
    EnVision: taking the pulse of our twin planet2012In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 33, no 2-3, p. 337-363Article in journal (Refereed)
    Abstract [en]

    EnVision is an ambitious but low-risk response to ESA's call for a medium-size mission opportunity for a launch in 2022. Venus is the planet most similar to Earth in mass, bulk properties and orbital distance, but has evolved to become extremely hostile to life. EnVision's 5-year mission objectives are to determine the nature of and rate of change caused by geological and atmospheric processes, to distinguish between competing theories about its evolution and to help predict the habitability of extrasolar planets. Three instrument suites will address specific surface, atmosphere and ionosphere science goals. The Surface Science Suite consists of a 2.2 m(2) radar antenna with Interferometer, Radiometer and Altimeter operating modes, supported by a complementary IR surface emissivity mapper and an advanced accelerometer for orbit control and gravity mapping. This suite will determine topographic changes caused by volcanic, tectonic and atmospheric processes at rates as low as 1 mm a (-aEuro parts per thousand 1). The Atmosphere Science Suite consists of a Doppler LIDAR for cloud top altitude, wind speed and mesospheric structure mapping, complemented by IR and UV spectrometers and a spectrophotopolarimeter, all designed to map the dynamic features and compositions of the clouds and middle atmosphere to identify the effects of volcanic and solar processes. The Ionosphere Science Suite uses a double Langmiur probe and vector magnetometer to understand the behaviour and long-term evolution of the ionosphere and induced magnetosphere. The suite also includes an interplanetary particle analyser to determine the delivery rate of water and other components to the atmosphere.

  • 25. Gurnett, D. A.
    et al.
    Persoon, A. M.
    Groene, J. B.
    Kurth, W. S.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nichols, J. D.
    The rotation of the plasmapause-like boundary at high latitudes in Saturn's magnetosphere and its relation to the eccentric rotation of the northern and southern auroral ovals2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L21203-Article in journal (Refereed)
    Abstract [en]

    Here we present a study of the rotation of the plasmapause-like density boundary discovered by the Cassini spacecraft at high latitudes in the Saturnian magnetosphere, and compare the results with previously published studies of high-latitude magnetic field perturbations and the eccentric rotation of the auroral ovals. Near the planet the density boundary is located at dipole L values ranging from about 8 to 15, and separates a region of very low densities at high latitudes from a region of higher densities at lower latitudes. We show that the density boundary rotates at different rates in the northern and southern hemispheres, and that the periods are the same as the modulation periods of Saturn kilometric radiation in those hemispheres. We also show that the phase of rotation in a given hemisphere is closely correlated with the phase of the high-latitude magnetic field perturbations observed by Cassini in that hemisphere, and also with the phase of the eccentric rotation of the auroral oval observed by the Hubble Space Telescope.

  • 26.
    Hadid, Lina Z
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko W.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Cravens, T. E.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Hedman, M. M.
    Univ Idaho, Dept Phys, Moscow, ID USA.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 19, p. 10084-10092Article in journal (Refereed)
    Abstract [en]

    We present new results obtained by the Radio and Plasma Wave Science Langmuir probe on board Cassini during the Grand Finale. The total direct current sampled by the Langmuir probe at negative bias voltage is used to study the effect of the ring shadows on the structure of the Kronian topside ionosphere. The D and C rings and the Cassini Division are confirmed to be optically thin to extreme ultraviolet solar radiation. However, different responses from the opaque A and B rings are observed. The edges of the A ring shadow are shown to match the A ring boundaries, unlike the B ring, which indicates variable responses to the B ring shadow. We show that the variable responses are due to the ionospheric plasma, more precisely to the longer chemical lifetime of H+ compared to H-2(+) and H-3(+), suggesting that the plasma is transported from the sunlit region to the shadowed one in the ionosphere. Plain Language Summary As Saturn's northern hemisphere experienced summer during the Grand Finale, the planet's northern dayside hemisphere and its rings were fully illuminated by the Sun. However, the southern hemisphere was partly obscured because of the shadows cast by the A and B rings. Using the in situ measurements of the Langmuir probe part of the Radio and Plasma Wave Science investigation on board the Cassini spacecraft, we study for the first time the effect of the ring shadows on Saturn's ionosphere. From the ring shadows signatures on the total ion current collected by the Langmuir probe, we show that the A and B rings are optically thicker (to the solar extreme ultraviolet radiation) than the inner C and D rings and the Cassini Division to the solar extreme ultraviolet radiation. Moreover, we reproduce the boundaries of the A ring and the outer edge of the B ring. Furthermore, observed variations with respect to the inner edge of the B ring imply a delayed response of the ionospheric H+ because of its long lifetime and suggest that the ionospheric plasma is transported from an unshadowed region to a shadowed one in the ionosphere.

  • 27.
    Hadid, Lina Z
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko W
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Shebanits, O.
    Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London, England.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nagy, A. F.
    Univ Michigan, Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.
    Eriksson, Anders I
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Saturn's Ionosphere: Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 16, p. 9362-9369Article in journal (Refereed)
    Abstract [en]

    We present the electron density (n(e)) altitude profiles of Saturn's ionosphere at near-equatorial latitudes from all 23 orbits of Cassini's Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The n(e) profiles are shown to be more variable and connected to the D-ring below 5,000 km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the D-ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini's final plunge, where the main ionospheric peak is crossed at similar to 1,550-km altitude. Plain Language Summary The Cassini Langmuir probe measured directly the uppermost layer of Saturn's atmosphere, the ionosphere, during its Grand Finale. The observations revealed a layered electron density altitude profile with evidence in the southern hemisphere of an electrodynamic type of interaction with the planet innermost D-ring. Moreover, the main peak of the ionosphere is observed for the first time in the final plunge around 1,550 km.

  • 28.
    Herique, A.
    et al.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Agnus, B.
    UPMC Univ Paris 06, UVSQ Univ Paris Saclay, CNRS, LATMOS,IPSL, F-78280 Guyancourt, France.
    Asphaug, E.
    Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA;Arizona State Univ, Sch Earth & Space Explorat, Tempe, AZ 85287 USA.
    Barucci, A.
    LESIA, F-92195 Paris, France.
    Beck, P.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Bellerose, J.
    CALTECH, JPL, Pasadena, CA 91109 USA.
    Biele, J.
    German Aerosp Ctr DLR, D-51147 Cologne, Germany.
    Bonal, L.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Bousquet, P.
    CNES, F-3100 Toulouse, France.
    Bruzzone, L.
    Univ Trento, I-38123 Trento, Italy.
    Buck, C.
    Estec, ESA, NL-2200 AG Noordwijk, Netherlands.
    Carnelli, I.
    ESA HQ, F-75015 Paris, France.
    Cheng, A.
    JHU, APL, Laurel, MD 20723 USA.
    Ciarletti, V.
    UPMC Univ Paris 06, UVSQ Univ Paris Saclay, CNRS, LATMOS,IPSL, F-78280 Guyancourt, France.
    Delbo, M.
    Univ Cote Azur, Observ Cote Azur, CNRS, Lab Lagrange, F-06000 Nice, France.
    Du, J.
    Peking Univ, IRSGIS, Beijing 100871, Peoples R China.
    Du, X.
    Tech Univ Dresden, D-01069 Dresden, Germany.
    Eyraud, C.
    Aix Marseille Univ, CNRS, Cent Marseille, Inst Fresnel, F-13013 Marseille, France.
    Fa, W.
    Peking Univ, IRSGIS, Beijing 100871, Peoples R China.
    Fernandez, J. Gil
    Estec, ESA, NL-2200 AG Noordwijk, Netherlands.
    Gassot, O.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Granados-Alfaro, R.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Green, S. F.
    Open Univ, Milton Keynes MK7 6AA, Bucks, England.
    Grieger, B.
    ESAC, ESA, Madrid 28692, Spain.
    Grundmann, J. T.
    DLR German Aerosp Ctr, Inst Space Syst, D-28359 Bremen, Germany.
    Grygorczuk, J.
    ASTRONIKA Sp Zoo, PL-00716 Warsaw, Poland.
    Hahnel, R.
    Tech Univ Dresden, D-01069 Dresden, Germany.
    Heggy, E.
    CALTECH, JPL, Pasadena, CA 91109 USA;Univ Southern Calif, Viterbi Sch Engn, Los Angeles, CA 90089 USA.
    Ho, T-M
    Karatekin, O.
    Observ Royal Belgique, B-1180 Brussels, Belgium.
    Kasaba, Y.
    Tohoku Univ, Dept Geophys, Sendai, Miyagi 9808578, Japan.
    Kobayashi, T.
    Korea Inst Geosci & Mineral Resources, Geol Res Ctr, Daejeon 34132, South Korea.
    Kofman, W.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France;PAS, Space Res Ctr, PL-00716 Warsaw, Poland.
    Krause, C.
    German Aerosp Ctr DLR, D-51147 Cologne, Germany.
    Kumamoto, A.
    Tohoku Univ, Dept Geophys, Sendai, Miyagi 9808578, Japan.
    Kuppers, M.
    ESAC, ESA, Madrid 28692, Spain.
    Laabs, M.
    Tech Univ Dresden, D-01069 Dresden, Germany.
    Lange, C.
    DLR German Aerosp Ctr, Inst Space Syst, D-28359 Bremen, Germany.
    Lasue, J.
    Univ Toulouse, UPS OMP, IRAP, Toulouse, France;CNRS, IRAP, 9 Ave Colonel Roche,BP 44346, F-31028 Toulouse 4, France.
    Levasseur-Regourd, A. C.
    UVSQ UPSay, Sorbonne Univ, UPMC Sorbonne Univ, CNRS,INSU,LATMOS IPSL, F-75252 Paris, France.
    Mallet, A.
    CNES, F-3100 Toulouse, France.
    Michel, P.
    Univ Cote Azur, Observ Cote Azur, CNRS, Lab Lagrange, F-06000 Nice, France.
    Mottola, S.
    German Aerosp Ctr DLR, Inst Planetary Res, D-12489 Berlin, Germany.
    Murdoch, N.
    Univ Toulouse, Inst Super Aeronaut & Espace ISAE SUPAERO, F-31000 Toulouse, France.
    Muetze, M.
    Tech Univ Dresden, D-01069 Dresden, Germany.
    Oberst, J.
    German Aerosp Ctr DLR, Inst Planetary Res, D-12489 Berlin, Germany.
    Orosei, R.
    Ist Nazl Astrofis, Ist Radioastron, I-40129 Bologna, Italy.
    Plettemeier, D.
    Tech Univ Dresden, D-01069 Dresden, Germany.
    Rochat, S.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    RodriguezSuquet, R.
    CNES, F-3100 Toulouse, France.
    Rogez, Y.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Schaffer, P.
    Tech Univ Dresden, D-01069 Dresden, Germany.
    Snodgrass, C.
    Open Univ, Milton Keynes MK7 6AA, Bucks, England.
    Souyris, J-C
    Tokarz, M.
    ASTRONIKA Sp Zoo, PL-00716 Warsaw, Poland.
    Ulamec, S.
    German Aerosp Ctr DLR, D-51147 Cologne, Germany.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Zine, S.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.
    Direct observations of asteroid interior and regolith structure: Science measurement requirements2018In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, no 8, p. 2141-2162Article in journal (Refereed)
    Abstract [en]

    Our knowledge of the internal structure of asteroids is, so far, indirect - relying entirely on inferences from remote sensing observations of the surface, and theoretical modeling of formation and evolution. What are the bulk properties of the regolith and deep interior? And what are the physical processes that shape asteroid internal structures? Is the composition and size distribution observed on the surface representative of the bulk? These questions are crucial to understand small bodies' history from accretion in the early Solar System to the present, and direct measurements are needed to answer these questions for the benefit of science as well as for planetary defense or exploration. Radar is one of the main instruments capable of sounding asteroids to characterize internal structure from sub-meter to global scale. In this paper, we review the science case for direct observation of the deep internal structure and regolith of a rocky asteroid of kilometer size or smaller. We establish the requirements and model dielectric properties of asteroids to outline a possible instrument suite, and highlight the capabilities of radar instrumentation to achieve these observations. We then review the expected science return including secondary objectives contributing to the determination of the gravitational field, the shape model, and the dynamical state. This work is largely inherited from MarcoPolo-R and AIDA/AIM studies.

  • 29. Hill, T. W.
    et al.
    Thomsen, M. F.
    Tokar, R. L.
    Coates, A. J.
    Lewis, G. R.
    Young, D. T.
    Crary, F. J.
    Baragiola, R. A.
    Johnson, R. E.
    Dong, Y.
    Wilson, R. J.
    Jones, G. H.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Mitchell, D. G.
    Horanyi, M.
    Charged nanograins in the Enceladus plume2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. A05209-Article in journal (Refereed)
    Abstract [en]

    There have been three Cassini encounters with the south-pole eruptive plume of Enceladus for which the Cassini Plasma Spectrometer (CAPS) had viewing in the spacecraft ram direction. In each case, CAPS detected a cold dense population of heavy charged particles having mass-to-charge (m/q) ratios up to the maximum detectable by CAPS (similar to 10(4) amu/e). These particles are interpreted as singly charged nanometer-sized water-ice grains. Although they are detected with both negative and positive net charges, the former greatly outnumber the latter, at least in the m/q range accessible to CAPS. On the most distant available encounter (E3, March 2008) we derive a net (negative) charge density of up to similar to 2600 e/cm(3) for nanograins, far exceeding the ambient plasma number density, but less than the net (positive) charge density inferred from the RPWS Langmuir probe data during the same plume encounter. Comparison of the CAPS data from the three available encounters is consistent with the idea that the nanograins leave the surface vents largely uncharged, but become increasingly negatively charged by plasma electron impact as they move farther from the satellite. These nanograins provide a potentially potent source of magnetospheric plasma and E-ring material.

  • 30.
    Holmberg, M. K. G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Swedish Inst Space Phys, Uppsala, Sweden..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, N.
    Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Garnier, P.
    Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Genot, V.
    Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Gilbert, L. K.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England..
    Density Structures, Dynamics, and Seasonal and Solar Cycle Modulations of Saturn's Inner Plasma Disk2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 12, p. 12258-12273Article in journal (Refereed)
    Abstract [en]

    We present statistical results from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe measurements recorded during the time interval from orbit 3 (1 February 2005) to 237 (29 June 2016). A new and improved data analysis method to obtain ion density from the Cassini LP measurements is used to study the asymmetries and modulations found in the inner plasma disk of Saturn, between 2.5 and 12 Saturn radii (1 RS = 60, 268 km). The structure of Saturn's plasma disk is mapped, and the plasma density peak, n(max), is shown to be located at similar to 4.6 RS and not at the main neutral source region at 3.95 RS. The shift in the location of n(max) is due to that the hot electron impact ionization rate peaks at similar to 4.6 RS. Cassini RPWS plasma disk measurements show a solar cycle modulation. However, estimates of the change in ion density due to varying EUV flux is not large enough to describe the detected dependency, which implies that an additional mechanism, still unknown, is also affecting the plasma density in the studied region. We also present a dayside/nightside ion density asymmetry, with nightside densities up to a factor of 2 larger than on the dayside. The largest density difference is found in the radial region 4 to 5 RS. The dynamic variation in ion density increases toward Saturn, indicating an internal origin of the large density variability in the plasma disk rather than being caused by an external source origin in the outer magnetosphere.

  • 31.
    Holmberg, Madeleine K. G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, M. W.
    Persoon, A. M.
    Ion densities and velocities in the inner plasma torus of Saturn2012In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 73, no 1, p. 151-160Article in journal (Refereed)
    Abstract [en]

    We present plasma data from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP), mapping the ion density and velocity of Saturn's inner plasma torus. Data from 129 orbits, recorded during the period from the 1st of February 2005 to the 27th of June 2010, are used to map the extension of the inner plasma torus. The dominant part of the plasma torus is shown to be located in between 2.5 and 8 Saturn radii (1 RS=60,268 km) from the planet, with a north-southward extension of ±2RS. The plasma disk ion density shows a broad maximum in between the orbits of Enceladus and Tethys. Ion density values vary between 20 and 125 cm-3 at the location of the density maximum, indicating considerable dynamics of the plasma disk. The equatorial density structure, |z|&lt;0.5RS, shows a slower decrease away from the planet than towards. The outward decrease, from 5 R S, is well described by the relation neq=2.2×10 4(1/R)3.63. The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm-3, only present at the south side of the ring plane. A less prominent density peak, of 115 cm-3, is also detected at the orbit of Tethys, at ∼4.9 RS. No density peaks are recorded at the orbits of the moons Mimas, Dione, and Rhea. The presented ion velocity vi,θ shows a clear general trend in the region between 3 and 7 RS, described by vi, θ=1.5R2-8.7R+39. The average vi,θ starts to deviate from corotation at around 3 RS, reaching ∼68% of corotation close to 5 RS.

  • 32.
    Holmberg, Mika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 11, p. 3717-3723Article in journal (Refereed)
    Abstract [en]

    We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4–6 RS (1 RS = 60,268 km) from the center of Saturn. The ion densities ni vary from an average of ∼35 cm−3 around noon up to ∼70 cm−3 around midnight. The ion velocities vi,θ vary from ∼28–32 km/s at the lowest dayside values to ∼36–40 km/s at the highest nightside values. The day/night asymmetry is suggested to be due to the radiation pressure force acting on negatively charged nanometer-sized dust of the E ring. This force will introduce an extra grain and ion drift component equivalent to the force of an additional electric field of 0.1–2 mV/m for 10–50 nm sized grains.

  • 33.
    Holmberg, Mika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cassidy, Tim
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA.
    Andrews, David
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Transport and chemical loss rates in Saturn's inner plasma disk2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 3, p. 2321-2334Article in journal (Refereed)
    Abstract [en]

    The Kronian moon Enceladus is constantly feeding its surrounding with new gas and dust, from cryovolcanoes located in its south polar region. Through photoionization and impact ionization of the neutrals a plasma disk is created, which mainly contains hydrogen ions H+ and water group ions W+. This paper investigates the importance of ion loss by outward radial transport and ion loss by dissociative recombination, which is the dominant chemical loss process in the inner plasma disk. We use plasma densities derived from several years of measurements by the Cassini Radio and Plasma Wave Science (RPWS) electric field spectrums and Langmuir probe (LP), to derive the total flux tube content NL2. Our calculation show that NL2 agrees well with earlier estimates within L shell 8. We also show that loss by transport dominates chemical loss in between L shell 2.5 and 10. The loss rate by transport is ∼5 times larger at 5 Saturn radii (1 RS = 60,268 km) and the difference is increasing as L7.7 for larger radial distances, for the total ion population. Chemical loss may still be important for the structure of the plasma disk in the region closest to Enceladus (∼±0.5 RS) at 3.95 RS, since the transport and chemical loss rates only differ by a factor of ∼2 in this region. We also derive the total plasma content of the plasma disk from L shell 4 to 10 to be 1.9×10^33 ions, and the total ion source rate for the same region to be 5.8×10^27 s^−1. The equatorial ion production rate P, ranges from 2.6×10^−5 cm^−3s^−1 (at L = 10) to 1.1×10^−4 cm^−3s^−1 (at L = 4.8). The net mass loading rate is derived to be 123 kg/s for L shell 4 to 10. 

  • 34. Jinks, S. L.
    et al.
    Bunce, E. J.
    Cowley, S. W. H.
    Provan, G.
    Yeoman, T. K.
    Arridge, C. S.
    Dougherty, M. K.
    Gurnett, D. A.
    Krupp, N.
    Kurth, W. S.
    Mitchell, D. G.
    Morooka, M.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cassini multi-instrument assessment of Saturn's polar cap boundary2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 10, p. 8161-8177Article in journal (Refereed)
    Abstract [en]

    We present the first systematic investigation of the polar cap boundary in Saturn's high-latitude magnetosphere through a multi-instrument assessment of various Cassini in situ data sets gathered between 2006 and 2009. We identify 48 polar cap crossings where the polar cap boundary can be clearly observed in the step in upper cutoff of auroral hiss emissions from the plasma wave data, a sudden increase in electron density, an anisotropy of energetic electrons along the magnetic field, and an increase in incidence of higher-energy electrons from the low-energy electron spectrometer measurements as we move equatorward from the pole. We determine the average level of coincidence of the polar cap boundary identified in the various in situ data sets to be 0.34 degrees 0.05 degrees colatitude. The average location of the boundary in the southern (northern) hemisphere is found to be at 15.6 degrees (13.3 degrees) colatitude. In both hemispheres we identify a consistent equatorward offset between the poleward edge of the auroral upward directed field-aligned current region of similar to 1.5-1.8 degrees colatitude to the corresponding polar cap boundary. We identify atypical observations in the boundary region, including observations of approximately hourly periodicities in the auroral hiss emissions close to the pole. We suggest that the position of the southern polar cap boundary is somewhat ordered by the southern planetary period oscillation phase but that it cannot account for the boundary's full latitudinal variability. We find no clear evidence of any ordering of the northern polar cap boundary location with the northern planetary period magnetic field oscillation phase.

  • 35.
    Knudsen, D. J.
    et al.
    Univ Calgary, Dept Phys & Astron, Calgary, AB, Canada.
    Burchill, J. K.
    Univ Calgary, Dept Phys & Astron, Calgary, AB, Canada.
    Buchert, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gill, Reine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Åhlén, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Smith, M.
    COM DEV Int, Cambridge, ON, Canada.
    Moffat, B.
    Univ Waterloo, Ctr Educ Math & Comp, Waterloo, ON, Canada;COM DEV Int, Cambridge, ON, Canada.
    Thermal ion imagers and Langmuir probes in the Swarm electric field instruments2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 2, p. 2655-2673Article in journal (Refereed)
    Abstract [en]

    The European Space Agency's three Swarm satellites were launched on 22 November 2013 into nearly polar, circular orbits, eventually reaching altitudes of 460 km (Swarm A and C) and 510 km (Swarm B). Swarm's multiyear mission is to make precision, multipoint measurements of low-frequency magnetic and electric fields in Earth's ionosphere for the purpose of characterizing magnetic fields generated both inside and external to the Earth, along with the electric fields and other plasma parameters associated with electric current systems in the ionosphere and magnetosphere. Electric fields perpendicular to the magnetic field.B are determined through ion drift velocity v(i) and magnetic field measurements via the relation.E. = -.vi x.B. Ion drift is derived from two-dimensional images of low-energy ion distribution functions provided by two Thermal Ion Imager (TII) sensors viewing in the horizontal and vertical planes;v(i) is corrected for spacecraft potential as determined by two Langmuir probes (LPs) which also measure plasma density ne and electron temperature T-e. The TII sensors use a microchannel-plate-intensified phosphor screen imaged by a charge-coupled device to generate high-resolution distribution images (66 x 40 pixels) at a rate of 16 s(-1). Images are partially processed on board and further on the ground to generate calibrated data products at a rate of 2 s(-1); these include.vi,.E., and ion temperature T-i in addition to electron temperature Te and plasma density n(e) from the LPs.

  • 36.
    Lamy, L.
    et al.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Zarka, P.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Cecconi, B.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Prange, R.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hospodarsky, G.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hunt, G. J.
    Imperial Coll London, Blackett Lab, London SW7 2BW, England.
    The low-frequency source of Saturn's kilometric radiation2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, no 6410, article id eaat2027Article in journal (Refereed)
    Abstract [en]

    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-kiloelectron 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.

  • 37. Lavvas, Panayotis
    et al.
    Yelle, Roger V.
    Koskinen, Tommi
    Bazin, Axel
    Vuitton, Veronique
    Vigren, Erik
    Galand, Marina
    Wellbrock, Anne
    Coates, Andrew J.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Crary, Frank J.
    Snowden, Darci
    Aerosol growth in Titan's ionosphere2013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 8, p. 2729-2734Article in journal (Refereed)
    Abstract [en]

    Photochemically produced aerosols are common among the atmospheres of our solar system and beyond. Observations and models have shown that photochemical aerosols have direct consequences on atmospheric properties as well as important astrobiological ramifications, but the mechanisms involved in their formation remain unclear. Here we show that the formation of aerosols in Titan's upper atmosphere is directly related to ion processes, and we provide a complete interpretation of observed mass spectra by the Cassini instruments from small to large masses. Because all planetary atmospheres possess ionospheres, we anticipate that the mechanisms identified here will be efficient in other environments as well, modulated by the chemical complexity of each atmosphere.

  • 38. Luhmann, J. G.
    et al.
    Ulusen, D.
    Ledvina, S. A.
    Mandt, K.
    Magee, B.
    Waite, J. H.
    Westlake, J.
    Cravens, T. E.
    Robertson, I.
    Edberg, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ma, Y. -J
    Wei, H.
    Russell, C. T.
    Dougherty, M. K.
    Investigating magnetospheric interaction effects on Titan's ionosphere with the Cassini orbiter Ion Neutral Mass Spectrometer, Langmuir Probe and magnetometer observations during targeted flybys2012In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 219, no 2, p. 534-555Article in journal (Refereed)
    Abstract [en]

    In the similar to 6 years since the Cassini spacecraft went into orbit around Saturn in 2004, roughly a dozen Titan flybys have occurred for which the Ion Neutral Mass Spectrometer (INMS) measured that moon's ionospheric density and composition. For these, and for the majority of the similar to 60 close flybys probing to altitudes down to similar to 950 km, Langmuir Probe electron densities were also obtained. These were all complemented by Cassini magnetometer observations of the magnetic fields affected by the Titan plasma interaction. Titan's ionosphere was expected to differ from those of other unmagnetized planetary bodies because of significant contributions from particle impact due to its magnetospheric environment. However, previous analyses of these data clearly showed the dominance of the solar photon source, with the possible exception of the nightside. This paper describes the collected ionospheric data obtained in the period between Cassini's Saturn Orbit Insertion in 2004 and 2009, and examines some of their basic characteristics with the goal of searching for magnetospheric influences. These influences might include effects on the altitude profiles of impact ionization by magnetospheric particles at the Titan orbit location, or by locally produced pickup ions freshly created in Titan's upper atmosphere. The effects of forces on the ionosphere associated with both the draped and penetrating external magnetic fields might also be discernable. A number of challenges arise in such investigations given both the observed order of magnitude variations in the magnetospheric particle sources and the unsteadiness of the magnetospheric magnetic field and plasma flows at Titan's (similar to 20Rs (Saturn Radius)) orbit. Transterminator flow of ionospheric plasma from the dayside may also supply some of the nightside ionosphere, complicating determination of the magnetospheric contribution. Moreover, we are limited by the sparse sampling of the ionosphere during the mission as the Titan interaction also depends on Saturn Local Time as well as possible intrinsic asymmetries and variations of Titan's neutral atmosphere. We use organizations of the data by key coordinate systems of the plasma interaction with Titan's ionosphere to help interpret the observations. The present analysis does not find clear characteristics of the magnetosphere's role in defining Titan's ionosphere. The observations confirm the presence of an ionosphere produced mainly by sunlight, and an absence of expected ionospheric field signatures in the data. Further investigation of the latter, in particular, may benefit from numerical experiments on the inner boundary conditions of 3D models including the plasma interaction and features such as neutral winds.

  • 39. Ma, Y. J.
    et al.
    Russell, C. T.
    Nagy, A. F.
    Toth, G.
    Dougherty, M. K.
    Wellbrock, A.
    Coates, A. J.
    Garnier, P.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cravens, T. E.
    Richard, M. S.
    Crary, F. J.
    The importance of thermal electron heating in Titan's ionosphere: Comparison with Cassini T34 flyby2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A10213-Article in journal (Refereed)
    Abstract [en]

    We use a new magnetohydrodynamic (MHD) model to study the effects of thermal-electron heating in Titan's ionosphere. This model improves the previously used multispecies MHD model by solving both the electron and ion pressure equations instead of a single plasma pressure equation. This improvement enables a more accurate evaluation of ion and electron temperatures inside Titan's ionosphere. The model is first applied to an idealized case, and the results are compared in detail with those of the single-pressure MHD model to illustrate the effects of the improvement. Simulation results show that the dayside ionosphere thermal pressure is larger than the upstream pressure during normal conditions, when Titan is located in the dusk region; thus Saturn's magnetic field is shielded by the highly conducting ionosphere, similar to the interaction of Venus during solar maximum conditions. This model is also applied to a special flyby of Titan, the T34 flyby, which occurred near the dusk region. It is shown that better agreement with the magnetometer data can be achieved using the two-fluid MHD model with the inclusion of the effects of thermal electron heating. The model results clearly demonstrate the importance of thermal-electron heating in Titan's ionosphere.

  • 40. Mandt, Kathleen E.
    et al.
    Gell, David A.
    Perry, Mark
    Waite, J. Hunter, Jr.
    Crary, Frank A.
    Young, David
    Magee, Brian A.
    Westlake, Joseph H.
    Cravens, Thomas
    Kasprzak, Wayne
    Miller, Greg
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Heays, Alan N.
    Lewis, Brenton R.
    Gibson, Stephen T.
    de la Haye, V.
    Liang, Mao-Chang
    Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. E10006-Article in journal (Refereed)
    Abstract [en]

    The Cassini Ion Neutral Mass Spectrometer (INMS) has measured both neutral and ion species in Titan's upper atmosphere and ionosphere and the Enceladus plumes. Ion densities derived from INMS measurements are essential data for constraining photochemical models of Titan's ionosphere. The objective of this paper is to present an optimized method for converting raw data measured by INMS to ion densities. To do this, we conduct a detailed analysis of ground and in-flight calibration to constrain the instrument response to ion energy, the critical parameter on which the calibration is based. Data taken by the Cassini Radio Plasma Wave Science Langmuir Probe and the Cassini Plasma Spectrometer Ion Beam Spectrometer are used as independent measurement constraints in this analysis. Total ion densities derived with this method show good agreement with these data sets in the altitude region (similar to 1100-1400 km) where ion drift velocities are low and the mass of the ions is within the measurement range of the INMS (1-99 Daltons). Although ion densities calculated by the method presented here differ slightly from those presented in previous INMS publications, we find that the implications for the science presented in previous publications is mostly negligible. We demonstrate the role of the INMS ion densities in constraining photochemical models and find that (1) cross sections having high resolution as a function of wavelength are necessary for calculating the initial photoionization products and (2) there are disagreements between the measured ion densities representative of the initial steps in Titan photochemistry that require further investigation.

  • 41.
    Menietti, J. D.
    et al.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Averkamp, T. F.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Ye, S. -Y
    Horne, R. B.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Woodfield, E. E.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Shprits, Y. Y.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA.;MIT, Dept Earth Atmospher & Planetary Sci, Cambridge, MA USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Survey of Saturn Z-mode emission2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 8, p. 6176-6187Article in journal (Refereed)
    Abstract [en]

    Because of the role of Z-mode emission in the diffusive scattering and resonant acceleration of electrons, we conduct a survey of intensity in the Saturn inner magnetosphere. Z mode is primarily observed as 5kHz narrowband emission in the lower density regions where the ratio of cyclotron to plasma frequency, f(c)/f(p)>1 to which we limit this study. This occurs at Saturn along the inner edge of the Enceladus torus near the equator and at higher latitudes. We present profiles and parametric fits of intensity as a function of frequency, radius, latitude, and local time. The magnetic field intensity levels are lower than chorus, but the electric field intensities are comparable. We conclude that Z-mode wave-particle interactions may make a significant contribution to electron acceleration in the inner magnetosphere of Saturn, supplementing acceleration produced by chorus emission.

  • 42.
    Menietti, J. D.
    et al.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Averkamp, T. F.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Ye, S. -Y
    Sulaiman, A. H.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hospodarsky, G. B.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Analysis of Intense Z-Mode Emission Observed During the Cassini Proximal Orbits2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 14, p. 6766-6772Article in journal (Refereed)
    Abstract [en]

    The role of Z-mode emission in the diffusive scattering and resonant acceleration of electrons is believed to be important at Saturn. A survey of the 5kHz component of this emission at Saturn earlier reported strong intensity in the lower density regions where the ratio of plasma frequency to cyclotron frequency, f(p)/f(c)<1. At Saturn this occurs along the inner edge of the Enceladus torus near the equator and at higher latitudes. Using the Cassini Radio and Plasma Wave Science instrument observations during the Cassini proximal orbits, we have now identified these emissions extending down to and within the ionosphere. Wave polarization measurements and unique frequency cutoffs are used to positively identify the wave mode. Analogous to the role of whistler mode chorus at Earth, Saturn Z-mode emissions may interact with electrons contributing to the filling or depleting of Saturn's inner radiation belts.

  • 43. Morooka, M. W.
    et al.
    Wahlund, J. -E
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, A. I.
    Farrell, W. M.
    Gurnett, D. A.
    Kurth, W. S.
    Persoon, A. M.
    Shafiq, M.
    André, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, M. K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Correction to \ldquoDusty plasma in the vicinity of Enceladus\rdquo2012In: Journal of Geophysical Research (Space Physics), ISSN 2169-9402, Vol. 117, no A3Article in journal (Refereed)
    Abstract [en]

    <A href=”/journals/ja/ja1203/2012JA017606/”>Abstract Available</A> from <A href=”http://www.agu.org”>http://www.agu.org</A>

  • 44.
    Morooka, Michiko W.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Ye, S. -Y
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Farrell, W. M.
    NASA, GSFC, Greenbelt, MD USA.
    The Dusty Plasma Disk Around the Janus/Epimetheus Ring2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 6, p. 4668-4678Article in journal (Refereed)
    Abstract [en]

    We report on the electron, ion, and dust number densities and the electron temperatures obtained by the Radio and Plasma Wave Science instruments onboard Cassini during the Ring-Grazing orbits. The numerous ring passage observations show a consistent picture as follows: (1) Beyond 0.1 R-S above and below the equator the electron and ion densities are quasi-neutral with a distribution similar to the one obtained in the plasma disk. (2) A sharp ion density enhancement occurs at vertical bar Z vertical bar < 0.1 R-S, to more than 200 cm(-3) at the equator, while the electron density remains low only to values of 50cm(-3). The electron/ion density ratio is <= 0.1 at the equator. (3) Micrometer-sized dust has also been observed at the equator. However, the region of intense dust signals is significantly narrower (vertical bar Z vertical bar<0.02 R-S) than the enhanced ion density regions. (4) The electron temperature (T-e) generally decreases with decreasing Z with small T-e enhancements near the equator. We show that the dust size characteristics are different depending on the distance from the equator, and the large micrometer-sized grains are more perceptible in a narrow region near the equator where the power law slope of the dust size distribution becomes less steep. As a result, different scale heights are obtained for nanometer and micrometer grains. Throughout the ring, the dominant part of the negative charges is carried by the small nanometer-sized grains. The electron/ion density ratio is variable from orbit to orbit, suggesting changes in the dust charging over time scales of weeks. Plain Language Summary The Radio and Plasma Wave Science instrument onboard Cassini observed a dusty plasma during the Ring-Grazing orbits. Dusty plasma is composed of, in addition to the electrons and ions, charged dust grains, and those grains play an important role in the plasma dynamics. The observed electron, ion, and dust number densities and the electron temperatures showed the layered structure of the faint Janus/Epimetheus rings. The core of the dusty ring composed of micron-sized dust is surrounded by a dusty plasma consisting of the ions and the negatively charged nanometer grains and further surrounded by the pristine plasma. The electron/ion density ratio of the dusty plasma varies from orbit to orbit, implying that the dust charging characteristics of the dusty ring change over time scales of weeks.

  • 45.
    Morooka, Michiko W.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Farrell, W. M.
    Gurnett, D. A.
    Kurth, W. S.
    Persoon, A. M.
    Shafiq, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, Madeleine K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dusty plasma in the vicinity of Enceladus2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A12221-Article in journal (Refereed)
    Abstract [en]

    We present in situ Cassini Radio Plasma Wave Science observations in the vicinity of Enceladus and in the E ring of Saturn that indicate the presence of dusty plasma. The four flybys of Enceladus in 2008 revealed the following cold plasma characteristics: (1) there is a large plasma density (both ions and electrons) within the Enceladus plume region, (2) no plasma wake effect behind Enceladus was detected, (3) electron densities are generally much lower than the ion densities in the E ring (n(e)/n(i) < 0.5) as well as in the plume (n(e)/n(i) < 0.01), and (4) the average bulk ion drift speed is significantly less than the corotation speed and is instead close to the Keplerian speed. These signatures result from half or more of the electrons being attached to dust grains and by the interaction between the surrounding cold plasma and the predominantly negatively charged submicrometer-sized dust grains. The dust and plasma properties estimated from the observations clearly show that the dust-plasma interaction is collective. This strong dust-plasma coupling appears not only in the Enceladus plume but also in the Enceladus torus, typically from about 20 R(E) (similar to 5000 km) north and about 60 R(E) (similar to 15,000 km) south of Enceladus. We also suggest that the dust-plasma interaction in the E ring is the cause of the planetary spin-modulated dynamics of Saturn's magnetosphere at large.

  • 46.
    Morooka, Michiko
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hadid, Lina Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Waite, J. H.
    Southwest Res Inst, San Antonio, TX USA.
    Perryman, R. S.
    Southwest Res Inst, San Antonio, TX USA.
    Perry, M.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Saturn's Dusty Ionosphere2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 3, p. 1679-1697Article in journal (Refereed)
    Abstract [en]

    Measurements of electrons and ions in Saturn's ionosphere down to 1,500-km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spacecraft are presented. Five nearly identical deep ionosphere flybys during the Grand Finale orbits and the Final plunge orbit revealed a rapid increase in the plasma densities and discrepancies between the electrons and ions densities (N-e and N-i) near the closest approach. The small N-e/N-i ratio indicates the presence of a dusty plasma, a plasma which charge carrier is dominated by negatively charged heavy particles. Comparison of the Langmuir probe obtained density with the light ion density obtained by the Ion and Neutral Mass Spectrometer confirmed the presence of heavy ions. An unexpected positive floating potential of the probe was also observed when N-e/N-i << 1. This suggests that Saturn's ionosphere near the density peak is in a dusty plasma state consisting of negatively and positively charged heavy cluster ions. The electron temperature (T-e) characteristics in the ionosphere are also investigated and unexpectedly high electron temperature value, up to 5000 K, has been observed below 2,500-km altitude in a region where electron-neutral collisions should be prominent. A well-defined relationship between T-e and N-e/N-i ratio was found, implying that the electron heating at low altitudes is related to the dusty plasma state of the ionosphere.

  • 47. Romanelli, N.
    et al.
    Modolo, R.
    Dubinin, E.
    Berthelier, J. -J
    Bertucci, C.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Leblanc, F.
    Canu, P.
    Edberg, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Waite, H.
    Kurth, W. S.
    Gurnett, D.
    Coates, A.
    Dougherty, M.
    Outflow and plasma acceleration in Titan's induced magnetotail: Evidence of magnetic tension forces2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 12Article in journal (Refereed)
    Abstract [en]

    Cassini plasma wave and particle observations are combined with magnetometer measurements to study Titan's induced magnetic tail. In this study, we report and analyze the plasma acceleration in Titan's induced magnetotail observed in flybys T17, T19, and T40. Radio and Plasma Wave Science observations show regions of cold plasma with electron densities between 0.1 and a few tens of electrons per cubic centimeter. The Cassini Plasma Spectrometer (CAPS)-ion mass spectrometer (IMS) measurements suggest that ionospheric plasma in this region is composed of ions with masses ranging from 15 to 17 amu and from 28 to 31 amu. From these measurements, we determine the bulk velocity of the plasma and the Alfven velocity in Titan's tail region. Finally, a Walen test of such measurements suggest that the progressive acceleration of the ionospheric plasma shown by CAPS can be interpreted in terms of magnetic tension forces.

  • 48. Roussos, E.
    et al.
    Kollmann, P.
    Krupp, N.
    Paranicas, C.
    Krimigis, S. M.
    Mitchell, D. G.
    Persoon, A. M.
    Gurnett, D. A.
    Kurth, W. S.
    Kriegel, H.
    Simon, S.
    Khurana, K. K.
    Jones, G. H.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, Madeleine K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Energetic electron observations of Rhea's magnetospheric interaction2012In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 221, no 1, p. 116-134Article in journal (Refereed)
    Abstract [en]

    Saturn's moon Rhea is thought to be a simple plasma absorber, however, energetic particle observations in its vicinity show a variety of unexpected and complex interaction features that do not conform with our current understanding about plasma absorbing interactions. Energetic electron data are especially interesting, as they contain a series of broad and narrow flux depletions on either side of the moon's wake. The association of these dropouts with absorption by dust and boulders orbiting within Rhea's Hill sphere was suggested but subsequently not confirmed, so in this study we review data from all four Cassini flybys of Rhea to date seeking evidence for alternative processes operating within the moon's interaction region. We focus on energetic electron observations, which we put in context with magnetometer, cold plasma density and energetic ion data. All flybys have unique features, but here we only focus on several structures that are consistently observed. The most interesting common feature is that of narrow dropouts in energetic electron fluxes, visible near the wake flanks. These are typically seen together with narrow flux enhancements inside the wake. A phase-space-density analysis for these structures from the first Rhea flyby (R1) shows that Liouville's theorem holds, suggesting that they may be forming due to rapid transport of energetic electrons from the magnetosphere to the wake, through narrow channels. A series of possibilities are considered to explain this transport process. We examined whether complex energetic electron drifts in the interaction region of a plasma absorbing moon (modeled through a hybrid simulation code) may allow such a transport. With the exception of several features (e.g. broadening of the central wake with increasing electron energy), most of the commonly observed interaction signatures in energetic electrons (including the narrow structures) were not reproduced. Additional dynamical processes, not simulated by the hybrid code, should be considered in order to explain the data. For the small scale features, the possibility that a flute (interchange) instability acts on the electrons is discussed. This instability is probably driven by strong gradients in the plasma pressure and the magnetic field magnitude: magnetometer observations show clearly signatures consistent with the (expected) plasma pressure loss due to ion absorption at Rhea. Another potential driver of the instability could have been gradients in the cold plasma density, which are, however, surprisingly absent from most crossings of Rhea's plasma wake. The lack of a density depletion in Rhea's wake suggests the presence of a local cold plasma source region. Hybrid plasma simulations show that this source cannot be the ionized component of Rhea's weak exosphere. It is probably related to accelerated photoelectrons from the moon's negatively charged surface, indicating that surface charging may play a very important role in shaping Rhea's magnetospheric interaction region. (C) 2012 Elsevier Inc. All rights reserved.

  • 49.
    Royer, E. M.
    et al.
    Univ Colorado, LASP, Boulder, CO 80309 USA.
    Esposito, L. W.
    Univ Colorado, LASP, Boulder, CO 80309 USA.
    Crary, F.
    Univ Colorado, LASP, Boulder, CO 80309 USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Enhanced Airglow Signature Observed at Titan in Response to its Fluctuating Magnetospheric Environment2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 17, p. 8864-8870Article in journal (Refereed)
    Abstract [en]

    On rare occasions Titan has been observed in the magnetosheath, where the solar wind interferes with the regular magnetic field generated by Saturn. This particular orbital position allows for a deeper investigation of Titan's upper atmosphere response to its highly energetic magnetospheric environment. Although solar extreme ultraviolet radiation is known to be the main source of ionization in Titan's upper atmosphere, magnetospheric particle precipitation can also account for about 10% of the ionization process. We are reporting here on ultraviolet observations of Titan airglow enhancements occurring while the spacecraft and Titan are known to have been exposed to the magnetosheath environment. Using remote sensing Cassini Ultraviolet Imaging Spectrograph observations of Titan in correlation with in situ Cassini Plasma Spectrometer measurements, we present evidence of Titan's upper atmosphere response to an electron burst crossing the magnetosheath at the time of the T32 flyby, on 13 June 2007. Plain Language Summary Most of the time, Titan is embedded in Saturn's magnetosphere. The solar wind pressure on Saturn's magnetic field defines the size of the magnetospheric envelop around the planet. On rare occasion, this pressure is strong enough to reduce the size of Saturn's magnetospheric envelop, leaving Titan outside of it. We have been observing Titan and its immediate environment during such a configuration. The compression of the magnetic envelop allows for Titan uppermost layer of its atmosphere to directly interact with solar wind particles. We are reporting here on an observation showing a strong and sudden brightening of the upper atmosphere of Titan correlated with simultaneous measurements of an increase in electron energy around the satellite. Using remote sensing Cassini Ultraviolet Imaging Spectrograph observations of Titan in correlation with in situ Cassini Plasma Spectrometer measurements, we present evidence of Titan's upper atmosphere response to an electron burst passing by the Saturn's system at the time of the T32 flyby, on 13 June 2007, providing a better understanding of how magnetospheric environment and planetary atmospheres interact together.

  • 50. Sakai, S.
    et al.
    Watanabe, S.
    Morooka, M. W.
    Holmberg, Madeleine K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gurnett, D. A.
    Kurth, W. S.
    Dust-plasma interaction through magnetosphere-ionosphere coupling in Saturn's plasma disk2013In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 75, no 1, p. 11-16Article, review/survey (Refereed)
    Abstract [en]

    The ion bulk speeds in the equatorial region of Saturn's inner magnetosphere, according to data from the Langmuir Probe (LP) on board the Cassini spacecraft, are about 60% of the ideal co-rotation speed; the ion speeds are between the co-rotation and Keplerian speeds (Holmberg et al.; Ion densities and velocities in the inner plasma torus of Saturn, Planetary and Space Science). These findings suggest that sub-micrometer negatively charged E ring dust contributes to the plasma dynamics in the plasma disk. We calculated the ion speeds by using a multi-species fluid model, taking into account dust interactions to investigate the effects of ion-dust coulomb collision, mass loading, as well as taking into account magnetosphere-ionosphere coupling to investigate the effect of the magnetospheric electric field. The results show that the ion speeds can be significantly reduced by the electric fields generated by the collisions between ions and dusts when the dust density is high and the thickness of dust distribution is large. We also show that the ion speeds from our model are consistent with the LP observations when the maximum density of dust is larger than ∼105 m-3.

12 1 - 50 of 67
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf