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, From Systema Saturnium, Huygens (1659), Drawings of the first observations of Saturn with a telescope. I: Galileo (1610), II: Scheiner (1614)

, 2 Sketch drawn by Huygens, taken from Systema Saturnium, Huygens (1659)

, The date indicates March 25, 1655, at 8 in the evening. Bottom: Simulation of this observation and moon configuration, as what would have been seen from The Hague at 8 p.m. on March 25, 1655. This matches almost perfectly the top sketch, with the under-view of Saturn, and Titan on the right-hand side being slightly above the alignment of the ring plane, Top: Sketch by Huygens of Saturn (center) along with Titan (right, labeled "*a") taken from Systema Saturnium, Huygens (1659)

, 4 Sketch of Titan's perfectly circular orbit, by Huygens, determined to be slightly over 16 days, Systema Saturnium, 1659.

, Right: Two days before closest encounter with Saturn, Voyager 2 took this picture of Titan on August 23, 1981. A north polar collar is visible, with a brightness dichotomy between the southern and northern hemisphere. These observations indicated potential cloud circulation. Credit: NASA/JPL (PIA01532), Some of the first pictures taken of Saturn and Titan up-close. Top-left: Picture taken by Pioneer 11 upon arrival in September, 1979, about 2.8 × 10 6 km from Saturn. Titan is seen below Saturn. Credit: NASA Ames

, Left: The Cassini spacecraft with the Huygens probe to the right, atop the Titan IVB/Centaur rocket, awaiting its final shielding, weeks before launch. Credit: NASA. Right: Long exposure of the launch from Launch Pad 40, Cape Canaveral Air Station, Credit: NASA, vol.10

. Lebreton, Left: Cassini spacecraft diagram with its suite of 12 instruments (Section 1.3.3). Credit: NASA. Right: Two views of the Huygens probe, p.11, 2005.

. .. Waite, INMS enabled in situ analysis of neutrals and positive ions. The closed-source mode (upper) analyzed non-reactive neutrals (e.g. N 2 , CH 4 , while the open source configuration (lower) enabled measurements of reactive neutrals and positive ions with energies <100 eV, The final grand moments of Cassini. Left: the X-band up and down link radio signal (top) and the longer wavelength S-band downlink (bottom). The X-band signal started to drop at 4:55:39 a.m, p.14, 1996.

, Titan" in their title (from Web of Science) from 1945 (1 year after Kuiper, 1944) until Cassini-Huygens EOM (End Of Mission), Total number of publications including the word

, The five main fields of research implicated in the list of publications from Figure 1.11, showing the multidisciplinary resulting aspect of the mission

, HASI vertical temperature (red line) and pressure (black line) profiles measured during the Huygens descent

, Different ionization energy sources from the thermosphere to the surface, taken from Krasnopolsky (2009), with an ionizing peak at 1060 km (Solar Zenith Angle 60?)

. T19-inms-spectra-from-waite, Lower panel: neutral spectrum. Upper panel: positive ion correspondences, taken between 950 and 1000 km, 2007.

. T5-inms-nighttime-spectrum, Y. Vuitton, ;. .. Mcewan, and . Westlake, showing the densities of ions inferred from the neutral densities. The spectrum shown is averaged from spectra taken between 1027 and 1200 km, 2007.

. Vuitton, 24 1.19 10 dominant anion abundances found by Mukundan and Bhardwaj (2018) using updated cross-sections and reaction rate coefficients, of the same flyby as Figure 1, The CAPS-ELS negative ion spectrum, 2009.

, Condensation curves obtained for 15 neutrals, 2017.

A. , The broad haystack feature at 220 cm ?1 is attributed to an ice cloud absorption, potentially nitrile-rich, CIRS limb spectrum, 2014.

C. Adapted-from-lavvas and V. Kok, The haystack feature detected by Anderson et al. (2014) at ?125 km is shown as the blue dashed line. The red dashed line corresponds to the approximate HCN condensation altitude region as given by Barth (2017), and the gray shaded area below it is the saturation point of most other volatiles, p.28, 2008.

, 3 (Top) Pressure evolution of the gas products according to degassing time in a 90-10% (blue) and 99-1% N 2 -CH 4 (red) gas mixture. Labeled at each data point are the times and vessel pressures, respectively. The MS1 (-130?C, 0.38 mbar), MS2 (-79?C, 0.74 mbar), MS3 (+22?C, 1.84 mbar) color-coded labels correspond to the three spectra of Fig. 4 taken at their corresponding temperatures and pressures, No cryogenic trap. Mass spectra of a 90-10% N 2 -CH 4 mixture with plasma off (red) and plasma on (black). The consumption of methane at m/z 16 and its fragments m/z 15, vol.13

=. 10%, Plots marked in blue, red and black represent intermittent spectra taken 7 min, 76 min and 21h after commencing volatile release back to room temperature (MS1, MS2 and MS3, respectively)

, In black, the initial mass spectrum taken before release of the volatiles, still at low-controlled temperature (and representative of the blank of our mass spectrometer). In blue and brown, the final state of volatiles at, p.61

, N 2 -CH 4 plasma conditions, plotted with an arbitrary absorbance against a 650-4000 cm ?1 wavenumber range. The volatile density produced during the plasma discharge is being incrementally released and analyzed through IR spectroscopy. Top: Total gas pressures of 0.38 mbar (-130?C), 0.93 mbar (-66?C), 1.28 mbar (-44?C) and 1.84 mbar (+22?C) are shown in black, blue, cyan and red, respectively. Bottom: Total measured gas pressures of 0 mbar (-73?C), 0.12 mbar (-41?C), 0.20 mbar (-8?C) and 0.34 mbar (+22?C) with the same color code. One clear difference is in the absence of any substantial aliphatic compounds (2800-3100 cm ?1 ) at, FT-IR spectra of the volatiles taken after the 90-10% (top) and 99-1% (bottom)

, Top: Molecular densities and average interpolated kinetic profile of C 2 H 2 . Bottom: NH 3 and HCN. Approximate temperatures are also labeled over each data point. The error bars represent the dispersion of the data points for all three experiments, p.65

. .. , 66 3.9 [CH 4 ] 0 = 1%. Main absorption bands of (A) NH 3 (930 cm ?1 and 960 cm ?1 doublet), (B) C 2 H 2 (729.25 cm ?1 ), (C) HCN (713 cm-1), (D) C 2 H 4 (949.55 cm ?1 ). The color code is the same as in Figure 3.6. The vertical dashed gray lines correspond to the integration band used for the density calculations on either side of the absorption peaks, 8 10% methane conditions. Top: Molecular densities and average interpolate kinetic profiles of C 2 H 2 and C 2 H 4 . Bottom: NH 3 and HCN, p.75

, 3) of selected species, NH 3 (m/z 17), C 2 H 2 (m/z 26), HCN (m/z 27), C 2 H 4 (m/z 28) and CH 3 CN (m/z 41) over time, Evolution of the intensities (same time scale as Figure, vol.3

, In particular, the ion and neutral mass spectrometer is visible to the right of the chamber. The chamber and mass spectrometer are separated by a VAT valve, enabling a residual gas pressure within the transfer tube of 10 ?9 mbar. The residual pressure in the PAMPRE chamber is 10 ?6 mbar, The PAMPRE cold plasma chamber, along with its suite of instruments

, Schematic diagram of the two electrodes creating the plasma discharge, with the extractor head of the EQP extracting the ions from the plasma, vol.86

, The ions are extracted from the plasma by the transfer tube on the left-hand side. The extractor's floating potential enables the extraction of the positive ions. Then, the ions are guided by a series of lenses until they hit the multiple detector. We set the multiplier to 1800 V. The RF head analyzes the impacted particles and sends the counts to a computer, Diagram of the EQP by Hiden Analytics, vol.87

, 4 IED of m/z 32 in an O 2 plasma discharge. The vertical white dashed line indicates the energy peak for this ion, i.e. 0.6 V. This is the value that will be subsequently used hereafter

, Mass spectra in an O 2 plasma discharge, with the positive ion energy filter set at 0.6 V

, Mass spectra for [N 2 ?CH 4 ] 0 = 1% with m/z < 100. Four spectra are plotted, which overall, show similar ion distributions, p.91

, Mass spectra for [N 2 ?CH 4 ] 0 = 5% with m/z < 100, p.92

, Mass spectra for [N 2 ?CH 4 ] 0 = 10% with m/z < 100, p.92

, ] 0 = 1% mixing ratio for selected ions m/z 14, vol.16

, = 1% mixing ratio, with the positive ion energy filter set at 2.2 eV, i.e. the maximum energy for m/z 28 (see Figure 4.10)

, = 10% mixing ratio, with the the positive ion energy filter set at 1.2 V, i.e. the maximum energy for m/z 28 (see Figure 4.10)

, 5% and 10% mixing ratio, in black, purple and gray, respectively. The energy filter was settled at 2.2, 2.2 and 1.2 V for the experiments at 1%, 5% and 10%, respectively, p.98

. .. =-1%,

. .. =-1%,

. .. =-1%,

.. .. ,

, Comparison of three normalized mass spectra taken with 1% CH 4 and degraded at the same resolution of 1 amu. a) shows the entire normalized averaged spectrum in positive ion mode of Figures 4.144.17, b) was taken with the plasma discharge on in RGA neutral mode, with an electron energy of 70 V and filament emission of 5 µA in the same conditions. Lastly, c) is the neutral spectrum taken in our previous study, which analyzed the volatile products formed in N 2 -CH 4 mixtures and released after being cryotrapped. For more details on these results, the reader is referred to Chapter, 2019.

, Comparison of three normalized mass spectra taken with 10% CH 4 and degraded at the same resolution of 1 amu. a) shows the entire normalized averaged spectrum in positive ion mode of Figures 4.144.17, b) the spectrum was taken in RGA neutral mode with the plasma discharge on, with an electron energy of 70 V and filament emission of 5 µA under the same conditions. Lastly, c) is the neutral spectrum taken in our previous study, which analyzed the volatile products formed in N 2 -CH 4 mixtures and released after being cryotrapped, 2008.

, Mass spectrum taken by INMS during the outbound leg of the T40 flyby, at 1097 km. The mass plot is separated in 1 Da. bins and plotted against raw IP counts. The INMS operated in open source ion mode during this flyby in order to detect low energy ions (< 100 eV, p.109

, Mass spectrum taken during the outbound leg of the T40 flyby (in blue), at 1097 km, compared with our experimental averaged spectra taken in 1% CH 4 . The mass plot is separated in 1 Da, p.110

, Mass spectrum taken during the outbound leg of the T40 flyby (in blue), at 1097 km, compared with our experimental averaged spectra taken in 5% CH 4 . The mass plot is separated in 1 Da, p.111

. .. Bins, 111 experimental conditions, compared with 26 measurements during the inbound and outbound leg of T40, for an altitude range of 1000-1150 km. Mass data is all separated in 1 Da. bins and y axis values increase downward, Mass spectrum taken during the outbound leg of the T40 flyby

, Relative evolution trends of the main C 2 species in our three experimental conditions, compared with 26 measurements during the inbound and outbound leg of T40, for an altitude range of 1000-1150 km. Mass data is all separated in 1 Da. bins and y axis values increase downward

, species in our three experimental conditions, compared with 26 measurements during the inbound and outbound leg of T40, for an altitude range of 1000-1150 km. Mass data is all separated in 1 Da. bins and y axis values increase downward, vol.3

, species in our three experimental conditions, compared with 26 measurements during the inbound and outbound leg of T40, for an altitude range of 1000-1150 km. Mass data is all separated in 1 Da. bins and y axis values increase downward, vol.4

, 125 4.30 IED with a [N 2 ?CH 4 ] 0 = 5% mixing ratio for m/z 28. The maximum is at 2.2 V. As the two previous conditions have shown similar IEDs for all ions, and tholins are rapidly produced at 5% CH 4 , we only obtained an IED for m/z 28, vol.14, p.28

D. Kok, with the detection of an HCN cloud in the winter polar vortex (blue) at 300 km. Red and green correspond to the illuminated surface and non-LTE emission, respectively. The presence of HCN ice particles at these high altitudes was unexpected and explained by an efficient post-equinox cooling, 2014.

, The sample holder containing the sapphire window is at the center. It can be rotated over 360 ? . The MCT corresponds to the Mercury Cadmium Telluride infrared detector, 2 Acquabella chamber top-view diagram, 2015.

, On the left-hand side, the chamber surrounded by the FTIR, the spray nozzle, the UV-VIS CCD detector and cooling system

, The sample holder holds a sapphire window substrate, with a N 2 -CH 4 10% yellowish-coated tholin deposition, produced in the PAMPRE reactor. The sapphire windows are cleaned with isopropanol and in an ultrasonic bath in between experiments to remove any roomtemperature residue

, 139 5.6 The ramp under a fume hood that we used, connected to a primary pump, on the right. The HCN is synthesized in the Schlenk flask (see inset), transferred to the manifold until the pressure is stable, and finally reaches the cryogenic chamber. The flask seen in the upper-right corner contains the stearic acid in excess, and the KCN as a white powder, Schematics of the substrate/sample holder setup in UV-VIS transmission configuration

, Schematic diagram of an HCN-C 4 H 2 deposition performed at 80K. ..142 5.8 A mass spectrum taken at 80K during an HCN-C 4 H 2 deposition. HCN is visible at m/z 27, with its CN fragment at m/z 26. C 4 H 2 at m/z 50 and its m/z 49 and m/z 48 fragments are also visible, p.142

. .. Nm, 146 5.11 IR spectrum of pure HCN ice taken at 70K. The ? 1 and ? 2 fundamentals are clearly distinguishable at 3126 cm ?1 and 2099 cm ?1 , respectively.147 5.12 HCN ice evolution after an accumulation of a 6h irradiation at 320 nm. No significant HCN consumption is seen, UV-VIS interference fringes, for pure HCN ice sample deposited atop a 1% CH 4 tholin film

, 149 5.15 HCN coated on a 10% CH 4 tholin sample. The successive irradiation does not seem to affect the ice film, 13 IR spectrum of pure HCN ice deposited on a 1% CH 4 tholin film at 70K.149 5.14 HCN coated on a 1% CH 4 tholin sample

, Residual gas analysis measurements of a few select species, during irradiation of our sample. The reason for the absence of any volatile products detected in our chamber during irradiation can be instrumental or that the putative chemistry occurs in the solid phase, p.151

H. An, C 4 H 2 UV absorption spectrum, showing the important photosensitivity of C 4 H 2 in the UV

, 18 IR spectrum of an HCN -C 4 H 2 mixture taken at 80K. The first two HCN modes dominate the spectrum, while the 2? 3 overtone also peaks out. C 4 H 2 is visible through its ? 4 C -H stretch, and less importantly the ? 5 C ---C stretch

, The ? 2 fundamental of HCN, showing its consumption centered at 2105 cm ?1 , after a 12h accumulated irradiation at 355 nm. This consumption is accompanied by an increasing active compound at a slightly lower frequency of 2098 cm ?1

, The ? 2 fundamental of C 4 H 2 , showing its consumption centered at 3272 cm ?1 , after a 12h accumulated irradiation at 355 nm, p.155

, Relative area losses due to photochemical consumption for C 4 H 2 (top) and HCN (middle and bottom), of their respective bands. Each data point corresponds to the area calculated under each band after the 7 irradiations

. Mcdonald, aimed at simulating (i) the gas phase volatile chemistry in N 2 /CH 4 mixtures using complementary energy sources (plasma discharges, UV lamps, synchrotron beam lines...), (ii) specific neutral and ion reaction pathways and low-temperature kinetics, (iii) tholin solid-state photochemistry in the lower atmosphere and cloud nucleation in the lower atmosphere, and (iv) the interaction between tholin material and hydrocarbon liquids, and lacustrine evaporation rates, List of some historical and current complementary experimental methods with their corresponding references, 1966.

O. Gupta, ;. Ponnamperuma, and . Scattergood, 16 Imanaka and Smith, vol.14, p.25, 1966.

. Couturier-tamburelli, , p.38, 1975.

, Vapor pressures P sub (mbar) calculated at 93K (-180?C) for HCN, C 2 H 2 and C 2 H 4 . The T p and A i columns correspond to the triple points and coefficients of the polynomials of extrapolations, respectively, 2009.

, For more details on the bands and absorption cross-sections used for the molecular density calculations, the reader is referred to Table 3 and Figures 9 and 10 of the Supplementary Material, vol.2, 1984.

, IR peak locations, fundamental frequencies and integrated wavenumber ranges, absorption cross-sections (cm 2 .molecule ?1 ) for each selected volatile, as analyzed in both methane conditions. For the calculation results

. Sharpe, , 2004.

=. 1%, for three different data sets. T 1?6 correspond to measurements done at approximately 30 min (-130?C), 60 min (-85?C), 120 min (-70?C), 180 min (-41?C), 1200 min (+22?C) and 1440 min (+22?C), respectively. Each column corresponds to one experiment. Number density calculations are performed with the integrated absorption cross-section of the ExoMol or Hitran databases at the resolution of our experimental spectra (see Table 3.3). Blank boxes indicate the absence of the species where no number density was derived

, for two different data sets. T 1?4 correspond to measurements done at approximately 7 min (-130?C), 125 min (-66?C), 190 min (-44?C) and 21h (+22?C), respectively. Each column corresponds to one experiment. Number density calculations are performed with the integrated absorption cross-section of the ExoMol or Hitran databases at the resolution of our experimental spectra (see Table 3.3). Blank boxes indicate the absence of the species where no number density was derived

, Global Environment Editor example for a given positive ion mass spectrum acquisition using the MASoft Hiden Analytics software. The Group column corresponds to the different components of the Electrostatic Quadrupole Plasma system, as shown in Figure 4.3. The second column represents all of the tunable variables, and their respective values, p.88

1. .. =1%, 2 Energy distribution maxima for, p.95

, Tentative attributions of several species from the C 1 ,C 2 ,C 3 and C 4 groups. These attributions are based on INMS observations and modeldependent calculated ion densities (Vuitton, Yelle, and McEwan, 2007.

, Pie charts representing the normalized mean intensities, for the C x molecular groups, as a function of the methane initial concentration (%)

.. .. ?-c-x-values,

, Pie charts of the first four C x H y N z groups of the T40 INMS spectrum taken at 1097 km, normalized by m/z 28

. Westlake, The m/z 29 contribution attributed to N 2 H + at 39% is only given in a nitrogen-rich mixture, denoted W2012, vol.122, 2012.

P. Couturier-tamburelli and G. Minaev, Gas-phase UV-Vis spectroscopic properties of HCN and C 4 H 2 , with their S 0 ground states, first excited singlet S 0 -S 1 and triplet S 0 -T 1 thresholds, 1994.

, 2 Compilation of all the experiments that were done with respective temperature, irradiation and mixing ratio conditions, p.144

, List of the 4 vibrational modes of gas phase HCN. 3a and 3b are degenerated modes. All are Raman and IR active

, The ? 4 and ? 5 vibrational modes of C 4 H 2 seen Figure B.10, p.153

, List of all Titan flybys from the Prime through the Solstice Mission. Altitudes are given in km. SOI stands for Saturn Orbit Insertion, p.201

, Chaque diagramme représente la contribution de chacun des ions (parties colorées), normalisée sur l'ensemble du spectre (partie grise), Diagrammes circulaires illustrant la variabilité des ions positifs présents dans des décharges plasma à 1%, 5% et 10% de CH 4

, 22 Reaction {7}: CH + 5 conversion into C 2 H + 5

, Reaction {36}: Major ion reaction 1

, Reaction {37}: Major ion reaction 2

, Reaction {38}: Major ion reaction 3

, List of Reactions Reaction, vol.44