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Pre-biotic molecules and dynamics in the ionosphere of Titan: a space weather station perspective
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)
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 [en]
Saturn, Titan, Ionosphere, Langmuir Probe
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
URN: urn:nbn:se:uu:diva-248118OAI: diva2:798949
2015-02-18, Polhemsalen, Ångström laboratory, 14:10 (English)
Swedish National Space Board
Available from: 2015-04-08 Created: 2015-03-27 Last updated: 2015-04-08Bibliographically approved
List of papers
1. Negative ion densities in the ionosphere of Titan-Cassini RPWS/LP results
Open this publication in new window or tab >>Negative ion densities in the ionosphere of Titan-Cassini RPWS/LP results
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2013 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 84, 153-162 p.Article in journal (Refereed) Published
Abstract [en]

The Cassini spacecraft Radio and Plasma Wave Science (RPWS) Langmuir Probe (LP) provides in-situ measurements of Titan's ionosphere. We present here data from 47 deep flybys in the time period October 2004 July 2012 of charge densities of positive and negative ions as well as electrons. These densities have been mapped with respect to altitude and solar zenith angle (SZA) in an altitude range of 880-1400 km. The inferred electron number densities are consistent with earlier presented observational results. Negative ion charge densities exhibit a trend that exponentially increases towards lower altitudes within the covered altitude range. This is especially evident on the nightside of Titan (SZA > 110 degrees). The negative ion charge densities at the lowest traversed altitudes (near 960 km) are inferred to be in the range 300-2500 cm(-3). The results show that very few free electrons (n(e)/n(i)similar to 0.1-0.7) exist in the deepest regions (880-1050 km) of Titan's nightside ionosphere. Instead the deep nightside part of Titan's ionosphere is dominated by both negatively and positively charged heavy (> 100 amu) organic ions. We therefore believe a dust/aerosol-ion plasma exists here, similar to what is found in noctilucent clouds in Earth's mesosphere. 

Titan, Ionospheric physics, Cassini, Negative ions, Dust-plasma interaction
National Category
Natural Sciences
urn:nbn:se:uu:diva-206997 (URN)10.1016/j.pss.2013.05.021 (DOI)000322805100016 ()
Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2015-04-08Bibliographically approved
2. On Ion Drifts and Neutral Winds in Titan’s Thermosphere
Open this publication in new window or tab >>On Ion Drifts and Neutral Winds in Titan’s Thermosphere
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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.

Titan, Ionosphere Drifts, Ion Drifts
National Category
Fusion, Plasma and Space Physics
urn:nbn:se:uu:diva-248122 (URN)
Available from: 2015-03-27 Created: 2015-03-27 Last updated: 2015-04-08

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