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On Ion Drifts and Neutral Winds in Titan’s Thermosphere
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)
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.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Saturn’s largest moon Titan hosts an atmosphere with complex organic chemistry initiated partly in the ionosphere. The nightside chemistry may be influenced by the ion transport from the dayside ionosphere. In turn, ion transport (ion drifts) may be affected by the neutral winds, which cannot be measured directly by Cassini. In this study we derive the ion drifts along the spacecraft trajectories based on analysis of in-situ measurements of electron and ion fluxes, mean masses of positive and negative ions and the magnetic field. Data from Titan flybys TA to T100 (Oct 2005 - Apr 2014) is included in this study, 55 flybys are below 1400 km and 48 are below 1200 km altitude. Based on the measurements, three regions of the ionosphere were defined by altitude: 1) above 1600 km, ions are 𝐄×𝐁-drifting (frozen into the magnetic field), 2) 1100-1600 km, dynamo-region, ions drift partly in opposite directions (perpendicular to B) and 3) below 1100 km (upper limit depends on convection electric field strength), ions are following neutrals.

Keyword [en]
Titan, Ionosphere Drifts, Ion Drifts
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-248122OAI: oai:DiVA.org:uu-248122DiVA: diva2:798871
Available from: 2015-03-27 Created: 2015-03-27 Last updated: 2015-04-08
In thesis
1. Pre-biotic molecules and dynamics in the ionosphere of Titan: a space weather station perspective
Open this publication in new window or tab >>Pre-biotic molecules and dynamics in the ionosphere of Titan: a space weather station perspective
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Saturn’s largest moon Titan (2575 km radius) is the second largest in the Solar system. Titan is the only known moon with a fully developed nitrogen-rich atmosphere with ionosphere extending to ~2000 km altitude, hosting complex organic chemistry. One of the main scientific interests of Titan’s atmosphere and ionosphere is the striking similarity to current theories of those of 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 reviews the first half of the PhD project on the production of pre-biotic molecules in the atmosphere of Titan and early Earth, focusing on the ion densities and dynamics in Titan’s ionosphere derived from the in-situ measurements by the Cassini Langmuir probe.

One of the main results is the detection of significant, up to ~2300 cm-3, charge densities of heavy (up to ~13000 amu) negative ions in Titan’s ionosphere below 1400 km altitude. On the nightside of the ionosphere at altitudes below 1200 km, the heavy negative ion charge densities are comparable to the positive ion densities and are in fact the main negative charge carrier, making this region of the ionosphere exhibit properties of dusty plasma. The overall trend is the exponential increasing of the negative ion charge densities towards lower altitudes.

Another important result is the detection of ion drifts that between 880-1100 km altitudes in Titan’s ionosphere translate to neutral winds of 0.5-5.5 km/s. Ion drifts define three regions by altitude, the top layer (above ~1600 km altitude) where the ions are frozen into the background magnetic field, the dynamo region (1100 – 1600 km altitudes) where the ions are drifting in partly opposing directions due to ion-neutral collisions in the presence of the magnetic and electric fields and the bottom layer (below 1100 km altitude) of the ionosphere, where the ions are coupled to neutrals by collisions.

Place, publisher, year, edition, pages
Department of Physics and Astronomy, 2015. 38 p.
Keyword
Saturn, Titan, Ionosphere, Langmuir Probe
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-248118 (URN)
Presentation
2015-02-18, Polhemsalen, Ångström laboratory, 14:10 (English)
Opponent
Supervisors
Funder
Swedish National Space Board
Available from: 2015-04-08 Created: 2015-03-27 Last updated: 2015-04-08Bibliographically approved

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Fusion, Plasma and Space Physics

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