| 1. |
- Chatain, A., et al.
(författare)
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Re-Analysis of the Cassini RPWS/LP Data in Titan's Ionosphere : 2. Statistics on 57 Flybys
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:8
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Tidskriftsartikel (refereegranskat)abstract
- The ionosphere of Titan hosts a complex ion chemistry leading to the formation of organic dust below 1,200 km. Current models cannot fully explain the observed electron temperature in this dusty environment. To achieve new insight, we have re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science package. A first paper (Chatain et al., 2021) introduces the new analysis method and discusses the identification of four electron populations produced by different ionization mechanisms. In this second paper, we present a statistical study of the whole LP dataset below 1,200 km which gives clues on the origin of the four populations. One small population is attributed to photo- or secondary electrons emitted from the surface of the probe boom. A second population is systematically observed, at a constant density (similar to 500 cm(-3)), and is attributed to background thermalized electrons from the ionization process of precipitating particles from the surrounding magnetosphere. The two last populations increase in density with pressure, solar illumination and Extreme ultraviolet flux. The third population is observed with varying densities at all altitudes and solar zenith angles (SZA) except on the far nightside (SZA > similar to 140 degrees), with a maximum density of 2,700 cm(-3). It is therefore certainly related to the photo-ionization of the atmospheric molecules. Finally, a fourth population detected only on the dayside and below 1,200 km reaching up to 2000 cm(-3) could be photo- or thermo-emitted from dust grains.
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| 2. |
- Chatain, A., et al.
(författare)
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Re-Analysis of the Cassini RPWS/LP Data in Titan's Ionosphere : 1. Detection of Several Electron Populations
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:8
-
Tidskriftsartikel (refereegranskat)abstract
- Current models of Titan's ionosphere have difficulties in explaining the observed electron density and/or temperature. In order to get new insights, we re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science (RPWS) instrument. This is the first of two papers that present the new analysis method (current paper) and statistics on the whole data set. We suggest that between two and four electron populations are necessary to fit the data. Each population is defined by a potential, an electron density and an electron temperature and is easily visualized by a distinct peak in the second derivative of the electron current, which is physically related to the electron energy distribution function (Druyvesteyn method). The detected populations vary with solar illumination and altitude. We suggest that the four electron populations are due to photo-ionization, magnetospheric particles, dusty plasma and electron emission from the probe boom, respectively.
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| 3. |
- Desai, R. T., et al.
(författare)
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Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan's Ionosphere
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 844:2
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Hadid, Lina Z, et al.
(författare)
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Saturn's Ionosphere : Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale
- 2019
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 46:16, s. 9362-9369
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Shebanits, O., et al.
(författare)
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Saturn's near-equatorial ionospheric conductivities from in situ measurements
- 2020
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Cassini's Grand Finale orbits provided for the first time in-situ measurements of Saturn's topside ionosphere. We present the Pedersen and Hall conductivities of the top near-equatorial dayside ionosphere, derived from the in-situ measurements by the Cassini Radio and Wave Plasma Science Langmuir Probe, the Ion and Neutral Mass Spectrometer and the fluxgate magnetometer. The Pedersen and Hall conductivities are constrained to at least 10(-5)-10(-4) S/m at (or close to) the ionospheric peak, a factor 10-100 higher than estimated previously. We show that this is due to the presence of dusty plasma in the near-equatorial ionosphere. We also show the conductive ionospheric region to be extensive, with thickness of 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities from orbit 288 to 292.
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