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Titan’s ionosphere: A survey of solar EUV influences
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)ORCID iD: 0000-0001-9621-211x
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, Swedish Institute of Space Physics, Uppsala Division.ORCID iD: 0000-0002-2107-5859
Université de Toulouse, UPS-OMP, IRAP, Toulouse, France.; CNRS, IRAP, Toulouse, France.
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 7, 7491-7503 p.Article in journal (Refereed) Published
Abstract [en]

Effects of solar EUV on positive ions and heavy negative charge carriers (molecular ions, aerosol, and/or dust) in Titan’s ionosphere are studied over the course of almost 12 years, including 78 flybys below 1400 km altitude between TA (October 2004) and T120 (June 2016). The Radio and Plasma Wave Science/Langmuir Probe-measured ion charge densities (normalized by the solar zenith angle) show statistically significant variations with respect to the solar EUV flux. Dayside charge densities increase by a factor of ≈2 from solar minimum to maximum, while nightside charge densities are found to anticorrelate with the EUV flux and decrease by a factor of ≈3–4. The overall EUV dependence of the ion charge densities suggest inapplicability of the idealized Chapman theory below 1200 km in Titan’s ionosphere. Nightside charge densities are also found to vary along Titan’s orbit, with higher values in the sunward magnetosphere of Saturn compared to the magnetotail.

Place, publisher, year, edition, pages
2017. Vol. 122, no 7, 7491-7503 p.
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-329486DOI: 10.1002/2017JA023987ISI: 000407627100038OAI: oai:DiVA.org:uu-329486DiVA: diva2:1141837
Funder
Swedish National Space Board, Dnr 130/11:2, Dnr 166/14, Dnr 135/13Swedish Research Council, 621-2013-4191
Available from: 2017-09-16 Created: 2017-09-16 Last updated: 2017-11-16Bibliographically approved
In thesis
1. Titan’s ionosphere and dust: – as seen by a space weather station
Open this publication in new window or tab >>Titan’s ionosphere and dust: – as seen by a space weather station
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Titan, the largest moon of Saturn, is the only known moon with a fully developed nitrogen-rich atmosphere, its ionosphere is detectable as high as 2200 km above its surface and hosts complex organic chemistry. Titan’s atmosphere and ionosphere has striking similarities to current theories of these regions around Earth 3.5 billion years ago. The Cassini spacecraft has been in orbit around Saturn since 2004 and carries a wide range of instruments for investigating Titan’s ionosphere, among them the Langmuir probe, a “space weather station”, manufactured and operated by the Swedish Institute of Space Physics, Uppsala.

This thesis presents studies of positive ions, negative ions and negatively charged dust grains (also called aerosols) in Titan’s ionosphere using the in-situ measurements by the Cassini Langmuir probe, supplemented by the data from particle mass spectrometers. One of the main results is the detection of significant (up to about 4000 cm-3) charge densities of heavy (up to about 13800 amu/charge) negative ions and dust grains in Titan’s ionosphere below 1400 km altitude. The dust is found to be the main negative charge carrier below about 1100 km on the nightside/terminator ionosphere, forming a dusty plasma (also called “ion-ion” plasma). A new analysis method is developed using a combination of simultaneous observations by multiple instruments for a case study of four flybys of Titan’s ionosphere, further constraining the ionospheric plasma charge densities. This allows to predict a dusty plasma in the dayside ionosphere below 900 km altitude (thus declaring it a global phenomenon), as well as to empirically estimate the average charge of the negative ions and dust grains to between -2.5 and -1.5 elementary charges. The complete Cassini dataset spans just above 13 years, allowing to study effects of the solar activity on Titan’s ionosphere. From solar minimum to maximum, the increase in the solar EUV flux increases the densities by a factor of ~2 in the dayside ionosphere and, surprisingly, decreases by a factor of ~3-4 in the nightside ionosphere. The latter is proposed to be an effect of the ionospheric photochemistry modified by higher solar EUV flux. Modelling photoionization also reveals an EUV trend (as well as solar zenith angle and corotational plasma ram dependencies) in the loss rate coefficient.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 69 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1562
Keyword
Titan, Cassini, Ionosphere, Dusty plasma, Ion-ion plasma, Langmuir probe, aerosols, tholins
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-329490 (URN)978-91-513-0076-4 (ISBN)
Public defence
2017-11-03, Ångström 2005, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Swedish National Space Board, Dnr 130/11:2
Available from: 2017-10-12 Created: 2017-09-16 Last updated: 2017-10-18

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Shebanits, OlegVigren, ErikWahlund, Jan-ErikMorooka, MichikoEdberg, Niklas J. T.

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Shebanits, OlegVigren, ErikWahlund, Jan-ErikMorooka, MichikoEdberg, Niklas J. T.Mandt, KathleenWaite, Hunter
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Swedish Institute of Space Physics, Uppsala DivisionDepartment of Physics and Astronomy
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