TAC 2016 - Abstract book - Université de Reims Champagne

Transcription

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Titan Aeronomy & Climate
Workshop
Reims, France – June 2016
Motivation of the Workshop
The observations of the Cassini spacecraft since 2004 revealed that Titan, the largest moon of Saturn, has an
active climate cycle with a cloud cover related to the large scale atmospheric circulation, lakes of methane and
hyrdrocarbons with variable depth, a dried fluvial system witnessing a past wetter climate, dunes, and deep
changes in the weather and atmospheric structure as Titan went through the North Spring equinox. Moreover,
the upper atmosphere is now considered the cradle of complex chemistry leading to aerosol formation, as well
as the manifestation place of atmospheric waves. However, as the Cassini mission comes to its end, many
fundamental questions remain unresolved. . .
The objective of the workshop is to bring together international experts from different fields of Titan’s research
in order to have an overview of the current understanding, and to determine the remaining salient scientific
issues and the actions that could be implemented to address them. PhD students and post-doc researchers are
welcomed to present their studies. This conference aims to be a brainstorming event leaving abundant time for
discussion during oral and poster presentations.
Scientific Organizing Committee
B. Bézard
P. Lavvas
P. Rannou
C. Sotin
D. Strobel
R. West
R. Yelle
LESIA
GSMA
GSMA
JPL
Dep. of Earth & Planetary Sc.
JPL
LPL
Obs. Paris-Meudon
Univ. Reims Champagne-Ardenne
Univ. Reims Champagne-Ardenne
NASA/Caltech
J. Hopkin Univ.
NASA/Caltech
Univ. of Arizona
Local Organizing Committee (GSMA)
D. Cordier / T. Cours / P. Lavvas / B. Poty / P. Rannou / B. Seignovert
Financial and Logistics Support
FR
FR
FR
USA
USA
USA
USA
General information
Table of Contents
Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abstracts: Atmospheric structure and aeronomy . . .
Abstracts: Aerosols formation and properties . . . .
Abstracts: Composition and seasonal cycle . . . . . .
Abstracts: CH4 cycle (surface, clouds and rains) and
Abstracts: Posters . . . . . . . . . . . . . . . . . . . . . . .
Social Event . . . . . . . . . . . . . . . . . . . . . . . . . . .
Outreach . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
List of participants . . . . . . . . . . . . . . . . . . . . . . .
Authors index . . . . . . . . . . . . . . . . . . . . . . . . . .
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Location
The workshop will take place into l’Hotel de la Paix, in the center of Reims:
9 rue Buirette, 51100 Reims, France
More info on Reims could be find on the website of the workshop
TAC 2016
2 / 35
Schedule
Schedule
Monday 27
09:00
Welcome and general information
Atmospheric structure and aeronomy
Conveners: P. Lavvas and D. Snowden
09:15
09:35
09:55
10:15
10:35
11:15
11:35
11:55
12:15
14:00
Strobel et al.
Feofilov et al.
Coates et al.
Snowden et al.
Coffee break
Royer et al.
Crary
Dubois
Lunch
Desai et al.
14:20
Discussion
Comparative Planetary Nitorgen Atmospheres: Titan, Triton and Pluto
Non-LTE diagnostics of infrared radiation of Titan’s atmosphere
Titan’s plasma interaction: photoelectrons and negative ions
Explaining the high electron density observed during T57
Enhanced airglow at Titan
A survey of heavy ions in Titan’s ionosphere
Chemistry of neutral species in Titan’s ionosphere: an experimental approach
Cassini CAPS-ELS observations of carbon-based anions and aerosol growth in
Titan’s ionosphere
Aerosol Formation and Properties
Conveners: N. Carrasco and R. West
15:00
15:20
16:00
Vuitton et al.
Coffee break
Tigrine et al.
16:20
Gautier et al.
16:40
17:00
Carrasco et al.
Poster session
Titan’s Oxygen Chemistry and its Impact on Haze Formation
VUV photodynamics of free tholins nanoparticles investigated by imaging
Angle-Resolved Photoemission with the Synchrotron Radiation
Mass spectrometry investigation of Titan aerosols analogs formed with traces
of aromatic compounds
Nitrogen fractionation in Titan’s aerosols
Tuesday 28
09:00
09:20
09:40
10:00
Lavvas et al.
Seignovert et al.
West et al.
Fabiano et al.
10:20
11:00
Coffee break
Maltagliati et al.
11:20
11:40
12:00
13:45
Rannou et al.
Sotin et al.
Lunch
Discussion
Aerosol properties in Titan’s upper atmosphere
Aerosols particles properties in Titan’s Detached Haze Layer
Cassini ISS Observations of Titan’s Haze 2012-2016
Are Titan aerosols really tholins? Constraining the aerosol extinction coefficient from VIMS in the 4 to 5 µm range
A new description of Titan’s aerosol optical properties from the analysis of
VIMS Emission Phase Function observations
Titan’s aerosol optical properties with VIMS observations at the limb
Titan’s haze as seen by VIMS during solar occultation observations
Composition and Seasonal Cycle
Conveners: B. Bézard and V. Vuitton
14:25
Cordiner
14:45
15:05
15:45
Molter et al.
Coffee break
Jolly
16:05
16:25
16:45
Yelle et al.
Flasar et al.
Coustenis et al.
18:00
Social event
TAC 2016
Detection and mapping of organic molecules in Titan’s atmosphere using
ALMA
Isotopic Ratios in Nitrile Species on Titan using ALMA
Search for minor molecular compounds in Titan’s atmosphere using infrared
spectroscopy
Coupled, Nitrogen, Oxygen, Carbon and Ion Chemistry on Titan
Titan’s Temperature and Zonal Wind Structure and Seasonal Behavior
Cassini/CIRS results on Titan’s atmospheric properties changes since the
northern equinox
Visit of Lanson Champagne Cellar
3 / 35
Schedule
Wednesday 29
09:00
Vinatier et al.
09:20
09:40
10:00
Sylvestre et al.
Teanby et al.
Bjoraker et al.
10:20
11:00
11:20
12:00
Coffee break
Jennings
Discussion
Lunch
Seasonal variations in Titan’s stratosphere observed with Cassini/CIRS after
the northern spring equinox
Seasonal variations of C4 H2 , C2 N2 and C3 H4 in Titans lower stratosphere
Post-equinox evolution of Titan’s south-polar atmosphere
The Abundance of C6 H6 and HC3 N over Titan’s South Pole as winter approaches
Seasonal Evolution of Titan’s South Pole 220 cm−1 Cloud
CH4 Cycle and Climate
Conveners: S. Rafkin and C. Sotin
13:45
14:05
14:25
14:45
15:05
15:45
16:05
16:25
16:45
19:00
Young et al.
Lora et al.
Barth
Rafkin et al.
Coffee break
Lorenz
Tokano
Charnay et al.
Discussion
Outreach
Mapping Methane in Titan’s Atmosphere near Titan’s Surface
Constraining and Interpreting Titan’s Methane Hydrologic Cycle
Cloud formation in Titan’s Stratosphere
Towards More Realistic Simulation of Air-Sea Interaction over Lakes on Titan
How often does it rain on Titan? (And what happens when it does?)
Likelihood of nitrogen condensation in Titan’s present atmosphere
Paleoclimates on Titan: the case of a pure nitrogen atmosphere
Exploration of extra-terrestrial oceans
Monday 27
09:00
09:15
09:35
09:55
10:15
10:35
11:15
11:35
11:55
12:15
14:00
14:20
15:00
15:20
16:00
16:20
16:40
17:00
Welcome
Strobel et al.
Feofilov et al.
Coates et al.
Snowden et al.
Coffee break
Royer et al.
Crary
Dubois
Lunch
Desai et al.
Discussion
Vuitton et al.
Coffee break
Tigrine et al.
Gautier et al.
Carrasco et al.
Poster session
TAC 2016
Tuesday 28
09:00
09:20
09:40
10:00
10:20
11:00
11:20
11:40
12:00
13:45
14:25
14:45
15:05
15:45
16:05
16:25
16:45
18:00
Lavvas et al.
Seignovert et al.
West et al.
Fabiano et al.
Coffee break
Maltagliati et al.
Rannou et al.
Sotin et al.
Lunch
Discussion
Cordiner
Molter et al.
Coffee break
Jolly
Yelle et al.
Flasar et al.
Coustenis et al.
Social Event
Wednesday 29
09:00
09:20
09:40
10:00
10:20
11:00
11:20
12:00
13:45
14:05
14:25
14:45
15:05
15:45
16:05
16:25
16:45
19:00
Vinatier et al.
Sylvestre et al.
Teanby et al.
Bjoraker et al.
Coffee break
Jennings
Discussion
Lunch
Young et al.
Lora et al.
Barth
Rafkin et al.
Coffee break
Lorenz
Tokano
Charnay et al.
Discussion
Outreach
4 / 35
Monday
Abstracts: Atmospheric structure and aeronomy
Conveners: P. Lavvas and D. Snowden
Monday 27, 09:15 - 09:35
Comparative Planetary Nitorgen Atmospheres: Titan, Triton and Pluto
Darrell F. Strobel1 and Xun Zhu2
1
2
Johns Hopkins University
Johns Hopkins University Applied Physics Laboratory
Titan has a massive atmosphere in comparison to Triton and Pluto which are widely regarded as the largest endmembers of Kuiper-Belt objects and as ’twins’ with thin buffered N2 atmospheres controlled by interactions with
surface ices, primarily N2 and CH4 frost. But one can compare them with Titan’s upper atmosphere by noting that
14 microbars on Titan is at an altitude of approximately 400 km. At this level Titan has haze layers as Pluto does
and less so on Triton.
The talk will emphasize the fundamental role that CH4 plays in controlling the thermal structure of these atmospheres
and is one of the principal reasons for the differences in the thermal structure of Pluto’s and Triton’s atmospheres.
Titan and Pluto have in common photochemical production of nitriles at detectable abundances, whereas Triton does
not. The cold upper atmosphere of Pluto remains a mystery as the reported abundances of HCN are insufficient to
cool the atmosphere in contrast to Titan’s thermosphere.
Monday 27, 09:35 - 09:55
Non-LTE diagnostics of infrared radiation of Titan’s atmosphere
Artem Feofilov1 , Ladislav Rezac2 , Alexander Kutepov3 , Sandrine Vinatier4 , Michael
Rey5 , Andrew Nikitin6 and Vladimir Tyuterev5
1
2
3
4
5
6
Laboratory of Dynamic Meteorology/IPSL/FX-Conseil, CNRS, Ecole Polytechnique, Universite Paris-Saclay, France
Max-Planck Institute for Solar System Research, Goettingen, Germany
The Catholic University of America / NASA Goddard Space Flight Center, Greenbelt, MD, USA
LESIA, Observatoire de Paris-Meudon, Meudon, France
GSMA, University of Reims, France
QUAMER Laboratory of Tomsk University, Russia
Yelle (1991) and Garcia-Comas et al, (2011) demonstrated the importance of accounting for the local thermodynamic
equilibrium (LTE) breakdown in the middle and upper atmosphere of Titan for the interpretation of infrared radiances measured at these heights.
In this work, we make further advance in this field by:
• updating the non-LTE model of CH4 emissions in Titan’s atmosphere and including a new extended database
of CH4 spectroscopic parameters
• studying the non-LTE CH4 vibrational level populations and the impact of non-LTE on limb infrared emissions
of various CH4 ro-vibrational bands including those at 7.6 and 3.3 µm
• implementing our non-LTE model into the LTE-based retrieval algorithm applied by Vinatier et al., (2015) for
processing the Cassini/CIRS spectra.
We demonstrate that accounting for non-LTE leads to an increase in temperatures retrieved from CIRS 7.6 µm limb
emissions spectra (∼10 K at 600 km altitude) and estimate how this affects the trace gas density retrieval.
Finally, we discuss the effects of including a large number of weak one-quantum and combinational bands on the
calculated daytime limb 3.3 µm emissions and the impact they may have on the CH4 density retrievals from the
Cassini VIMS 3.3 µm limb emission observations.
References:
Yelle, R.V., Non-LTE models of Titan’s upper atmosphere, Astrophys. J., 383, 380–400, (1991).
García-Comas et al, Analysis of Titan CH4 3.3 µm upper atmospheric emission as measured by Cassini/VIMS, Icarus, 214(2), 571–583,
(2011).
Vinatier et al., Seasonal variations in Titan’s middle atmosphere during the northern spring derived from Cassini/CIRS observations,
Icarus, 250, 95-115, (2015).
TAC 2016
5 / 35
Monday
Monday 27, 09:55 - 10:15
Titan’s plasma interaction: photoelectrons and negative ions
Andrew Coates1 , Anne Wellbrock1 , Ravi Desai1 and Hunter Waite2
1
2
UCL-MSSL
SwRI
We present a review of some of the most important results from the CAPS electron spectrometer.These include the
role of photoelectrons and polar wind escape processes, and remarkable negative ion observations.
Monday 27, 10:15 - 10:35
The Spatial and Temporal Variability of Ion and Electron Precipitation in Titan’s
Atmosphere
Darci Snowden1 , Mike Smith1 and Theo Jimson1
1
Central Washington University
Previous work (e.g. Snowden et al. 2014) showed that energy deposition rates in Titan’s atmosphere due to the
precipitation of magnetospheric electrons and ions are small compared to the energy flux due to solar EUV. However,
some of these results relied on energy flux rates at Titan’s exobase calculated from Voyager 1 data or data from a
small number of Cassini flybys. Cassini has shown that the plasma environment around Titan is extremely variable
and that the Voyager 1 conditions are not characteristic of an average plasma environment. Therefore, we further
investigate the issue using particle tracing simulations for ions and a two-stream model for electrons in combination
with a 3D model of Titan’s induced magnetosphere. We find that energy deposition and ionization rates in Titan’s
atmosphere do not only depend on the upstream energy distribution of magnetospheric plasma near Titan (e.g.
plasma sheet or lobe-like), but also on the characteristics of Titan’s Alfven wing structure and the strength of the
induced field. Surprisingly, we find that the energy deposition and ionization rates in Titan upper atmosphere may be
higher when Titan is in Saturn’s magnetospheric lobes due reduced shielding of magnetospheric ions. Our simulations
confirm that the globally averaged energy deposition rates due to magnetospheric particles are smaller than solar
radiation.
Monday 27, 11:15 - 11:35
Enhanced airglow at Titan
Emilie Royer1 , Larry Esposito1 and Jan-Erik Wahlund2
1
2
University of Colorado-Boulder
Swedish Institut of Space Physics
The Cassini Ultraviolet Imaging Spectrograph (UVIS) instrument made thousand of observations of Titan since its
arrival in the Saturnian system in 2004, but only few of them have been analyzed yet. Using the imaging capability of UVIS combined to a big data analytics approach, we have been able to uncover an unexpected pattern
in this observations: on several occasions the Titan airglow exhibits an enhanced brightness by approximately a
factor of 2, generally combined with a lower altitude of the airglow emission peak. These events typically last from
10 to 30 minutes and are followed and preceded by an airglow of regular and expected level of brightness and altitude.
Observations made by the Cassini Plasma Spectrometer (CAPS) instrument onboard Cassini allowed us to correlate the enhanced airglow observed on T-32 with an electron burst. The timing of the burst and the level of
energetic electrons (1 keV) observed by CAPS correspond to a brighter and lower than typical airglow displayed
on the UVIS data. Furthermore, during T-32 Titan was inside the Saturn’s magnetosheath and thus more subject
to bombardment by energetic particles. However, our analysis demonstrates that the presence of Titan inside the
magnetosheath is not a necessary condition for the production of an enhanced airglow, as we detected other similar
events while Titan was within Saturn’s magnetosphere.
The study presented here aims to a better understanding of the interactions of Titan’s upper atmosphere with
its direct environment.
TAC 2016
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Monday
Monday 27, 11:35 - 11:55
A survey of heavy ions in Titan’s ionosphere
Frank Crary1
1
University of Colorado, LASP
The Cassini Plasma Spectrometer (CAPS) has observed heavy positive ions, with masses up to approximately 300
amu, as well as negative ions with even higher masses. The abundance and density of these positive ions have been
reported for selected encounters, especially during those where comparisons with Ion and Neutral Mass Spectrometer
(INMS) data are possible. The present work presents a survey of all available encounters, showing the density of ions
in various mass ranges and their spatial distribution. The influence of the broad mass distribution on ionospheric
conductivity will also be discussed.
Monday 27, 11:55 - 12:15
Chemistry of neutral species in Titan’s ionosphere: an experimental approach
David Dubois1
1
LATMOS
Titan’s gas phase atmospheric chemistry leading to the formation of solid organic aerosols can be simulated in
laboratory simulations. Typically, plasma reactors can be used to achieve Titan-like conditions. The discharge
induces photodissociation and photoionization processes to the N2 -CH4 mixture. It faithfully reproduces the electron
energy range of magnetospheric electrons entering Titan’s atmosphere and it can also approximate the solar UV input
at Titan’s ionosphere. In this context, it is deemed necessary to apply and exploit such a technique in order to better
understand the chemical reactivity occurring in Titan-like conditions.
In the present work, we use the Pampre cold dusty plasma experiment with an N2 -CH4 gaseous mixture under
controlled pressure and gas influx, hence, emphasizing on the gas phase which we know is key to the formation
of aerosols on Titan. An internal cryogenic trap has been developed to accumulate the gas products during their
production and facilitate their detection. Those are identified and quantified by in situ mass spectrometry and
infrared spectroscopy. We present here results from this experiment in an 90-10% N2 -CH4 mixing ratio, using a
quantitative approach on nitriles and polycyclic aromatic hydrocarbons.
Monday 27, 14:00 - 14:20
Cassini CAPS-ELS observations of carbon-based anions and aerosol growth in
Titan’s ionosphere
Ravindra Desai1 , Andrew Coates1 , Anne Wellbrock1 , Dhiren Kataria1 , Geraint Jones1 ,
Gethyn Lewis1 and J Waite2
1
2
Mullard Space Science Laboratory, University College London, UK.
Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA.
Cassini observations of Titans ionosphere revealed an atmosphere rich in positively charged ions with masses up to >
350 amu and negatively charged ions and aerosols with mass over charge ratios as high as 13,800 amu/q. The detection
of negatively charged molecules by the Cassini CAPS Electron Spectrometer (CAPS-ELS) was particularly surprising
and showed how the synthesis of large aerosol-size particles takes place at altitudes much greater than previously
thought. Here, we present further analysis into this CAPS-ELS dataset, through an enhanced understanding of the
instrument’s response function. In previous studies the intrinsic E/E energy resolution of the instrument did not
allow specific species to be identified and the detections were classified into broad mass ranges. In this study we use
an updated fitting procedure to show how the ELS mass spectrum can be resolved into specific peaks at multiples of
carbon-based anions up to > 100 amu/q. The negatively charged ions and aerosols in Titans ionosphere increase in
mass with decreasing altitude, the lightest species being observed close to Titan’s exobase of ∼1,450km and heaviest
species observed at altitudes < 950km. We identify key stages in this apparent growth process and report on key
intermediaries which appear to trigger the rapid growth of the larger aerosol-size particles.
TAC 2016
7 / 35
Aerosols formation and properties
Monday
Abstracts: Aerosols formation and properties
Conveners: N. Carrasco and R. West
Monday 27, 15:00 - 15:20
Titan’s Oxygen Chemistry and its Impact on Haze Formation
Veronique Vuitton1 , Nathalie Carrasco2 , Laurène Flandinet1 , Sarah Hörst3 , Stephen
Klippenstein4 , Panayotis Lavvas5 , François-Régis Orthous-Daunay1 , Roland Thissen1
and Roger Yelle6
1
Université Grenoble Alpes, CNRS, IPAG
Université Versailles St-Quentin, Sorbonne Universités, UPMC Univ. Paris 06, CNRS/INSU, LATMOS-IPSL
3
Department of Earth and Planetary Sciences, Johns Hopkins University
4
Chemical Sciences and Engineering Division, Argonne National Laboratory
2
5
6
Groupe de Spectroscopie Moléculaire et Atmosphérique, Université de Reims, Champagne-Ardenne, CNRS UMR 7331
Lunar and Planetary Laboratory, University of Arizona
Though Titan’s atmosphere is reducing with its 98% N2 , 2% CH4 and 0.1% H2 , CO is the fourth most abundant
molecule with a uniform mixing ratio of ∼50 ppm. Two other oxygen bearing molecules have also been observed in
Titan’s atmosphere: CO2 and H2 O, with a mixing ratio of ∼15 and ∼1 ppb, respectively. The physical and chemical
processes that determine the abundances of these species on Titan have been at the centre of a long-standing debate
as they place constraints on the origin and evolution of its atmosphere [1]. Moreover, laboratory experiments have
shown that oxygen can be incorporated into complex molecules, some of which are building blocks of life [2]. Finally,
the presence of CO modifies the production rate and size of tholins [3,4], which transposed to Titan’s haze may have
some strong repercussions on the temperature structure and dynamics of the atmosphere.
We present here our current understanding of Titan’s oxygen chemistry and of its impact on the chemical composition of the haze. We base our discussion on a photochemical model that describes the first steps of the chemistry
and on state-of-the-art laboratory experiments for the synthesis and chemical analysis of aerosol analogues. We used
a very-high resolution mass spectrometer (LTQ-Orbitrap XL instrument) to characterize the soluble part of tholin
samples generated from N2 /CH4 /CO mixtures at different mixing ratios and with two different laboratory set-ups.
These composition measurements provide some understanding of the chemical mechanisms by which CO affects particle formation and growth. Our final objective is to obtain a global picture of the fate and impact of oxygen on
Titan, from its origin to prebiotic molecules to haze particles to material deposited on the surface.
References:
[1] S.M. Hörst, V. Vuitton, R.V. Yelle, The origin of oxygen species in Titan’s atmosphere, J. Geophys. Res., 113, E10006 (2008).
[2] S.M. Hörst, R.V. Yelle, A. Buch, N. Carrasco, G. Cernogora, O. Dutuit, E. Quirico, E. Sciamma-O’Brien, M.A. Smith, Á. Somogyi,
C. Szopa, R. Thissen, V. Vuitton, Formation of amino acids and nucleotide bases in a Titan atmosphere simulation experiment,
Astrobiology, 12, 809-17 (2012).
[3] B. Fleury, N. Carrasco, T. Gautier, A. Mahjoub, J. He, C. Szopa, E. Hadamcik, A. Buch, G. Cernogora, Influence of CO on Titan
atmospheric reactivity, Icarus, 238, 221-9 (2014).
[4] S.M. Hörst and M.A. Tolbert, The effect of carbon monoxide on planetary haze formation, Astrophys. J., 781, 53 (2014).
Monday 27, 16:00 - 16:20
VUV photodynamics of free tholins nanoparticles investigated by imaging AngleResolved Photoemission with the Synchrotron Radiation
Sarah Tigrine1,2 , Laurent Nahon2 , Nathalie Carrasco1 and Gustavo Garcia-Macias2
1
2
LATMOS
Synchrotron SOLEIL
Thanks to the Cassini Huygens mission, it is now established that the aerosols appear from an altitude of 1,000 km
in Titan’s atmosphere. Once they are formed and through their descent towards the surface, those grains will still
interact with persistent UV/VUV radiations, at different energies, that can reach lower atmospheric layers. This interaction has some impact, for example on the radiative transfer or on the ionization yield of the atmospheric compounds.
Models are a good way to study those processes, but the lack of data on the refractive index or the absolute
TAC 2016
8 / 35
Monday
absorption/ionization cross subsections of the aerosols can be an obstacle.
In order to shed some light and quantify those processes, we ionize analogs of aerosols produced with the PAMPRE
experiment (LATMOS) on the SAPHIRS platform from the DESIRS VUV beamline at the synchrotron SOLEIL,
equipped with an aerodynamic lens. The aerosols are injected directly under vacuum as isolated free nanoparticles
and do not need to take the form of a film deposited on a substrate. The generated photoelectrons are then collected
with a Velocity Map Imaging detector and their energetic and angular signatures are analyzed using the ARPES
method (Angle-Resolved PhotoElectron Spectroscopy).
Both the nanoparticles size distribution and the incident wavelength determine the parameters governing the photoemission process (intra-particles electron mean free path, photon penetration depth) as revealed by the angular
distribution of the photoelectron showing in same cases a marked forward/backward asymmetry with respect to the
photon axis. Those parameters may provide us with information on the optical behavior of the aerosols. In addition
we can extract the ionization potential in direct connection with the absorption cross subsections of the aerosol, from
which altitude dependent photodynamics can be unraveled.
We will present here the experiments performed, at different VUV energies, on Titan’s aerosol analogs with the
ARPES method and show how the first results can have implications regarding Titan’s atmosphere overall optical
characteristics.
Monday 27, 16:20 - 16:40
Mass spectrometry investigation of Titan aerosols analogs formed with traces of
aromatic compounds
Thomas Gautier1 , Melissa Trainer2 , Joshua Sebree3 , Xiang Li4 , Veronica Pinnick4 , Stephanie
Getty2 and Will Brinckerhoff2
1
NPP - NASA Goddard Space Flight Center, Greenbelt, USA
NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, USA
3
University of Northern Iowa, Cedar Falls, USA
2
4
CRESST, University of Maryland, Baltimore, USA
The detection of benzene at ppm levels in Titan’s atmosphere [1] by Cassini’s Ion and Neutral Mass Spectrometer
(INMS) supports the idea that aromatic and heteroaromatic reaction pathways may play an important role in Titan’s aerosols formation. In laboratory studies it has been shown that these aromatic molecules are easily dissociated
by ultraviolet radiation and can therefore contribute significantly to aerosol formation [2] and be used to dope the
production of aerosol analogs [3].
In this work we investigate the effect on the aerosol composition and growth pattern of the chemical nature of
the aromatic reactant used to produce aerosol. Analysis are performed using Laser Desorption-Time of Flight mass
spectrometry (LD-TOF) and Fourier Transform Infrared Spectroscopy (FTIR)
Infrared analysis of our samples shows that inclusion of aromatic compounds as trace precursors allows to better
fit laboratory data to Titan aerosol spectra observed by Cassini [3,4]. The improvement is especially visible on the
far infrared (∼200 cm−1 ) bands observed by CIRS [5].
LDMS results show that the aerosol growth patterns depend both on the number of rings and on the nitrogen content
of the trace precursor used. We also perform MS/MS analysis on some prominent peaks of aerosol mass spectra.
This MS/MS approach allows us to identify some of the key compounds in the aerosol growth processes.
References:
[1] Waite et al. (2007), Ion Neutral Mass Spectrometer Results from the First Flyby of Titan, Science 316, 870-875
[2] Trainer et al. (2013), The Influence of Benzene as a Trace Reactant in Titan Aerosol Analogs, ApJL 766, L4
[3] Sebree et al. (2014), Titan aerosol analog absorption features produced from aromatics in the far infrared, Icarus 236, 146-152
[4] Gautier et al. (2015), Temperature and aging effects on the Far-Infrared absorption features of aromatic-based Titan aerosol analogs,
submitted in Icarus
[5] Anderson et al. (2011) Titan’s aerosol and stratospheric ice opacities between 18 and 500 µm: Vertical and spectral characteristics
from Cassini CIRS, Icarus 212, 762-778
TAC 2016
9 / 35
Monday/Tuesday
Monday 27, 16:40 - 17:00
Nitrogen fractionation in Titan’s aerosols
Nathalie Carrasco1 , Maia Kuga2 , Bernard Marty2 , Benjamin Fleury1 and Yves Marrocchi2
1
Université de Versailles Saint Quentin
2
Université de Lorraine
A strong nitrogen fractionation is found by Cassini in Titan’s atmosphere with the detection of 15N-rich HCN relative
to N2 . Photodissociation of N2 associated or not to self-shielding might involve 15N-rich radicals prone to incorporation into forming organics. However the isotopic composition is only available for very simple gaseous N-bearing
compounds, and the propagation and conservation of such a large N-isotopic fractionation upon polymerization is
actually out of reach with the instruments onboard Cassini. We will therefore present a first laboratory investigation
of the possible enrichment in the solid organic aerosols. We will also discuss the space instrumention required in the
future to answer this pending issue on Titan.
Tuesday 28, 09:00 - 09:20
Aerosol properties in Titan’s upper atmosphere
Panayotis Lavvas1 , Tommi Koskinen2 , Emilie Royer3 , Pascal Rannou1 and Robert West4
1
2
3
4
GSMA/CNRS
LPL
LASP
JPL
Multiple Cassini observations reveal that the abundant aerosol particles in Titan’s atmosphere are formed at high
altitudes, particularly in the thermosphere. They subsequently fall towards the lower atmosphere and in their path
their size, shape, and population change in reflection to the variable atmospheric condition. Although multiple
observations can help us retrieve information for the aerosol properties in the lower atmosphere, we have limited
information for the aerosol properties between their formation region in the thermosphere and the upper region of
the main haze layer or the detached aerosol layer. Observations at UV wavelengths are the only way to probe this
part of the atmosphere and help us retrieve the aerosol properties. The presentation will provide an overview of the
available observations, and discuss their implications for the production and evolution of Titan’s aerosols.
Tuesday 28, 09:20 - 09:40
Aerosols particles properties in Titan’s Detached Haze Layer
Benoît Seignovert1 , Pascal Rannou1 , Panayotis Lavvas1 and Robert West2
1
2
GSMA - Université Reims Champagne Ardenne, Reims, FR
Jet Propulsion Laboratory - California Institute of Technology, Pasadena, CA, USA
Titan’s Detached Haze Layer (DHL) first observed in 1983 by Rages and Pollack during the Voyager 2 [1] is a consistent spherical haze feature surrounding Titan’s upper atmosphere and detached from the main haze. Since 2005,
the Imaging Science Subsystem (ISS) instrument on board the Cassini mission performs a continuous survey of the
Titan’s atmosphere and confirmed its persistence at 500 km up to the equinox (2009) before its drop and disappearance in 2012 [2]. Previous analyses showed, that this layer corresponds to the transition area between small spherical
aerosols and large fractal aggregates and play a key role in the aerosols formation in Titan’s atmosphere [3-5].
In this study we perform UV photometric analyses on ISS observations taken from 2005 to 2007 based on radiative
transfer inversion to retrieve aerosols particles properties in the DHL (bulk and monomer size, fractal dimension and
local density).
References:
[1] Rages and Pollach, Icarus 55 (1983); [2] West, et al., Icarus 38 (2011); [3] Rannou, et al., Icarus 147 (2000); [4] Lavvas, et al., Icarus
201 (2009); [5] Cours, et al., ApJ Lett. 741 (2015)
TAC 2016
10 / 35
Tuesday
Tuesday 28, 09:40 - 10:00
Cassini ISS Observations of Titan’s Haze 2012-2016
Robert West1,2 , Pascal Rannou2 , Panayotis Lavvas2 and Aida Ovanessian1
1
2
JPL
Université Reims Champagne-Ardenne
Since approximately late 2012 the ’Detached’ haze layer that was so prominent in short-wavelength Cassini ISS
(Imaging Science Subsystem) images from 2004 to 2012 and also seen in Voyager images has not been detected in
Cassini images. This development provides an important clue to the nature of processes responsible for the haze
and its structure., although it is unclear yet how to interpret this as well as the evolution of the haze prior to its
disappearance. Here we provide details on the time evolution of the haze as it disappeared and as it has been observed
by the Cassini ISS from 2012 to the present.
Tuesday 28, 10:00 - 10:20
Are Titan aerosols really tholins? Constraining the aerosol extinction coefficient
from VIMS in the 4 to 5 µm range
Federico Fabiano1,2 , Bianca Dinelli2 , Marco Ridolfi1 , Manuel Lòpez Puertas3 , Alberto
Adriani4 , Maria Moriconi4 and Emiliano D’Aversa4
1
University of Bologna
ISAC - CNR Bologna
3
IAA - CSIC Granada
4
IAPS - INAF Roma
2
Since the very first images of Titan made by Voyager I, it was evident that the planet was covered by a thick reddish
haze that prevented the spacecraft from seeing the surface. In the last twenty years, various models have been
developed in order to explain the production and aggregation of complex organic molecules on Titan to produce haze
particles. In most models, the optical properties of the aerosol particles are usually assumed to be similar to those of
the tholins first produced in the lab by Khare et al. (1984).
However, the spectral properties of Titan aerosols inferred from CIRS and VIMS observations in the infrared are
significantly different from those of the lab tholins both in the NIR, around 3 µm, and in the FIR (Vinatier et al.,
2012; Rannou et al., 2010).
In this work, we analyze a collection of night-side VIMS limb spectra at stratospheric altitudes in the 4 to 5 µm region,
where no direct measurement of the aerosol extinction coefficient has been made so far. Our simulated spectra include
non-LTE emission due to CO and CH3 D and thermal emission from the aerosols. We find that the optical properties
of Titan’s aerosols in this spectral region are not compatible with those of the tholins produced in the lab (Khare et
al., 2002; Imanaka et al., 2004; Quirico et al., 2008) and infer the actual extinction coefficient in this spectral range
from VIMS observations. In particular, the prominent 4.6 µm peak in the tholins absorbance spectrum, due to C-N
stretching, appears to be shifted at smaller wavelengths, raising further questions about the actual composition of
Titan aerosols.
Tuesday 28, 11:00 - 11:20
A new description of Titan’s aerosol optical properties from the analysis of VIMS
Emission Phase Function observations
Luca Maltagliati1,2 , Sébastien Rodriguez1,3 , Christophe Sotin4 , Pascal Rannou5 , Bruno
Bézard2 and Thomas Cornet6
1
AIM CEA Saclay
LESIA Observatoire de Paris
3
Université Paris 7
4
JPL / LPG Nantes
5
GSMA Reims
2
6
ESAC/ESA
TAC 2016
11 / 35
Tuesday
The Huygens probe gave unprecedented information on the properties of Titan’s aerosols (vertical distribution, opacity
as a function of wavelength, phase function, single scattering albedo) by in-situ measurements (Tomasko et al. 2008).
Being the only existing in-situ atmospheric probing for Titan, this aerosol model currently is the reference for many
Titan studies (e.g. by being applied as physical input in radiative transfer models of the atmosphere). Recently a
reanalysis of the DISR dataset, corroborated by data from the Downward-Looking Visible Spectrometer (DLVS), was
carried out by the same group (Doose et al. 2016), leading to significant changes to the indications given by Tomasko
et al. (2008).
Here we present the analysis of the Emission Phase Function observation (EPF) performed by VIMS during the
Cassini flyby T88 (November 2012). An EPF observes the same spot on the surface (and thus the same atmosphere)
with the same emergence angle but with different incidence angles. In this way, our EPF allows, for the first time, to
have direct information on the phase function of Titan’s aerosols, as well as on other important physical parameters
of the aerosols as the behavior of their extinction as a function of wavelength and the single scattering albedo (also as
a function of wavelength) for the whole VIMS range (0.8-5.2 µm). The T88 EPF is composed of 25 VIMS datacubes
spanning a scattering angle range approximately from 0°to 70°.
We used the radiative transfer model described in Hirtzig et al. (2013) as baseline, updated with improved methane
(+ related isotopes) spectroscopy. By changing the aerosol description in the model, we found the combination of
aerosol optical parameters that fits best a constant aerosol column density over the whole set of the VIMS datacubes.
We confirmed that the new results from Doose et al. (2016) do improve the fit for what concerns the vertical profile
and the extinction as a function of wavelength. However, a different phase function with respect to what they propose
must be employed, especially in the trend towards the backscattering peak. We also find that darker aerosols are
needed in order to reproduce the value of the column opacity measured in-situ by Huygens.
Tuesday 28, 11:20 - 11:40
Titan’s aerosol optical properties with VIMS observations at the limb
Pascal Rannou1 , Benoît Seignovert1 , Stéphane Le Mouélic2 and Christophe Sotin3
1
Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, Reims, France
Laboratory de Planétoloogie et Géodynamique, Université de Nantes, France
3
Jet Propulsion Laboratory, NASA-Caltech, Pasadena, États-Unis
2
The study of Titan properties with remote sensing relies on a good knowledge of the atmosphere properties. The
in-situ observations made by Huygens combined with recent advances in the definition of methane properties enable
to model and interpret observations with a very good accuracy. Thanks to these progresses, we can analyze in this
work the observations made at the limb of Titan in order to retrieve information on the haze properties as its vertical
profiles but also the spectral behaviour between 0.88 and 5.2 µm. To study the haze layer and more generally the
source of opacities in the stratosphere, we use some observation made at the limb of Titan by the VIMS instrument
onboard Cassini. We used a model in spherical geometry and in single scattering, and we accounted for the multiple
scattering with a parallel plane model that evaluate the multiple scattering source function at the plane of the limb.
Our scope is to retrieve informations about the vertical distribution of the haze, its spectral properties, but also to
obtain details about the shape of the methane windows to desantangle the role of the methane and of the aerosols.
We started our study at the latitude of 55°N, with a image taken in 2006 with a relatively high spatial resolution
(for VIMS). Our preliminary results shows the spectral properties of the aerosols are the same whatever the altitude.
This is a consequence of the large scale mixing. From limb profile between 0.9 and 5.2 µm, we can probe the haze
layer from about 500 km (at 0.9 µm) to the ground (at 5.2 µm). We find that the vertical profile of the haze layer
shows three distinct scale heights with transitions around 250 km and 350 km. We also clearly a transition around
70-90 km that may be due to the top of a condensation layer.
TAC 2016
12 / 35
Tuesday
Tuesday 28, 11:40 - 12:00
Titan’s haze as seen by VIMS during solar occultation observations
Christophe Sotin1 , Ken Lawrence1 , Fang Xu1 , Robert West1 , Robert Brown2 , Kevin
Baines1 , Bonnie Buratti1 , Roger Clark3 and Phil Nicholson4
1
2
3
4
Jet Propulsion Laboratory - California Institute of Technology, Pasadena, CA, USA
Department of Planetary Sciences, University of Arizona, Tucson, USA
Planetary Science Institute, Tucson, AZ, USA
Department of Astronomy, Cornell University, Ithaca, USA
This study describe solar occultation observations of Titan’s atmosphere by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. These observations include two recent observations made in the last
few months. The solar occultation observations have been made at different latitudes and seasons, which allows us
to investigate the variability of the density profile of aerosols. We present the line curves in the different atmospheric
windows, and the data processing and the inversion method to retrieve vertical density profile. This unique data
set provides information on Titan’s opacity in the atmospheric windows, which is important to retrieve the surface
properties. It also provides information on the cross-subsection of the aerosols as a function of wavelength in the
wavelength range 1 to 5 micron.
TAC 2016
13 / 35
Composition and seasonal cycle
Tuesday
Abstracts: Composition and seasonal cycle
Conveners: B. Bézard and V. Vuitton
Tuesday 28, 14:25 - 14:45
Detection and mapping of organic molecules in Titan’s atmosphere using ALMA
Martin Cordiner1
1
NASA Goddard Space Flight Center
Titan’s atmospheric photochemistry results in the production of a wide range of organic molecules, including hydrocarbons, nitriles, aromatics and other complex species of possible pre-biotic relevance. Studies of Titan’s atmospheric
chemistry thus provide a unique opportunity to explore the origin and evolution of organic matter in primitive (terrestrial) planetary atmospheres. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful new
facility, well suited to the study of molecular emission from Titan’s upper and middle-atmosphere. Results will be
presented from our ongoing studies of Titan using ALMA data obtained during the period 2012-2014 [1,2], including
detection and mapping of emission from C2 H5 CN, HNC, HC3 N, CH3 CN and CH3 CCH. In addition, combining
data from multiple ALMA Band 6 observations, we obtained high-resolution spectra with unprecedented sensitivity,
enabling the first detection of C2 H3 CN (vinyl cyanide) on Titan, and derived a mean C2 H3 CN/C2 H5 CN abundance
ratio above 300 km of 0.3. Vinyl cyanide has recently been investigated as a possible constituent of (pre-biotic) vesicle
membranes in Titan’s liquid CH4 oceans [3]. Radiative transfer models and possible chemical formation pathways
for the detected molecules will be discussed. ALMA observations provide instantaneous snapshot mapping of Titan’s
entire Earth-facing hemisphere for gases inaccessible to previous studies, and therefore provide new insights into
photochemical production and transport, particularly at higher altitudes. Our maps show spatially resolved peaks in
Titan’s northern and southern hemispheres, consistent with the molecular distributions found in previous studies at
infrared wavelengths by Voyager and Cassini, but high-altitude longitudinal asymmetries in our nitrile data indicate
that the mesosphere may be more spatially variable than previously thought.
References:
[1] Cordiner, M. A., Nixon, C. A., Teanby, N. A., et al. (2014). ALMA Measurements of the HNC and HC3N Distributions in Titan’s
Atmosphere. ApJ, 795, L30.
[2] Cordiner, M. A., Palmer, M. Y., Nixon, C. A. et al. (2015). Ethyl Cyanide On
Titan: Spectroscopic Detection and Mapping Using ALMA. ApJ, 800, L14.
[3] Stevenson, J., Lunine, J., Clancy, P. (2015). Membrane alternatives in worlds without oxygen: Creation of an azotosome. Sci. Adv.,
1, e1400067.
Tuesday 28, 14:45 - 15:05
Isotopic Ratios in Nitrile Species on Titan using ALMA
Edward Molter1,2 , Conor Nixon1 , Martin Cordiner1,2 , Joseph Serigano3 , Patrick Irwin4 ,
Nicholas Teanby5 , Steven Charnley1 and Johan Lindberg1
1
NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, USA
Department of Physics, Catholic University of America, Washington, USA
3
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, USA
4
Atmospheric, Oceanic, and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, UK
5
School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, UK
2
The atmosphere of Titan is primarily composed of molecular nitrogen (N2 , ∼98%) and methane (CH4 , ∼2%), but also
hosts a myriad of trace organic species. Two of the simplest and most abundant of these are hydrogen cyanide (HCN)
and cyanoacetylene (HC3 N). The advent of ALMA provides the opportunity to observe rotational transitions in these
molecules and their isotopologues with unprecendented sensitivity and spatial resolution. We searched through the
ALMA archive for publicly available high-resolution observations of Titan as a flux calibrator source taken between
April and July 2014; each integration lasted around 160 seconds. Using spectra of HCN and HC3 N isotopologues
found in these data, we derive vertical abundance profiles and determine the isotopic ratios 14N/ 15N and 12C/ 13C
in these molecules. We also report the detection of a new HCN isotopologue on Titan, H13 C615 N, and use a high
signal-to-noise spectrum of DCN to determine the D/H ratio in HCN on Titan for the first time. These isotopic
ratios are leveraged to constrain the physical and chemical processes occurring in Titan’s atmosphere.
TAC 2016
14 / 35
Tuesday
Tuesday 28, 15:45 - 16:05
Search for minor molecular compounds in Titan’s atmosphere using infrared
spectroscopy
Antoine Jolly1
1
LISA-UPEC
The Composite Infrared Spectrometer (CIRS) on-board Cassini has recorded spectra in the far and mid-infrared since
2004 with a spectral resolution of up to 0.5 cm−1 .
Improvement in the spectroscopic parameters has led to the detection of 13C isotopologues of HC3 N (Jennings 2008)
and C4 H2 (Jolly 2010). The study on C2 N2 opens the way to the detection of 15N isotopologues whose abundances
could give some clues to understand the origin and the evolution of Titan’s atmosphere (Fayt 2012). The higher
accuracy of spectroscopic data used to model CIRS spectra enables the search for longer carbon chains on Titan such
as HC5 N, C6 H2 and C4 N2 . Intensity measurements and a careful analysis of high resolution data has led to the first
line lists for C4 N2 . No detection of this molecule was possible but a precise abundance upper limit of C4 N2 in the
gas phase in Titan’s atmosphere could be determined (Jolly 2015).
Photochemical models of Titan’s atmosphere predict significant amount of allene (CH2 CCH2 ) and butane (C4 H10 ).
Allene reacts chemically very similarly to its isomer propyne (CH3 CCH) which is easily detected in the infrared.
Butane is supposed to be almost as abundant as propane (C3 H8 ) which has a large number of infrared signatures in
the CIRS spectra of Titan’s atmosphere. And yet, both hydrocarbons have not been detected on Titan so far.
Low temperature spectra down to 150 K have been recorded in the mid and far infrared at the AILEs beamline of the
SOLEIL synchrotron facility. Line lists or pseudo line lists have been compiled to search for the infrared signature of
those molecules in the CIRS spectra of Titan’s atmosphere.
Tuesday 28, 16:05 - 16:25
Coupled, Nitrogen, Oxygen, Carbon and Ion Chemistry on Titan
Roger Yelle1 , Véronique Vuitton2 , Panayotis Lavvas3 , Stephen Klippenstein4 and Sarah
Hörst5
1
Dept of Planetary Sciences, University of Arizona
2
Université Grenoble Alpes, CNRS, IPAG
Groupe de Spectroscopie Moléculaire et Atmosphérique, Université de Reims
4
Chemical Sciences and Engineering Division, Argonne National Laboratory
5
Department of Earth and Planetary Sciences, Johns Hopkins University
3
We present simulations of the coupled nitrogen, oxygen, and ion chemistry on Titan using a state-of-the-art photochemical model. The model is one dimensional and extends from the surface to the exobase. The chemistry
linking 160 neutral species and 172 ion species is described through networks including 1139 neutral reactions and
4361 ion reactions. UV photolysis of 59 species is included as well as dissociation and ionization of 16 species due to
suprathermal electrons. Reaction rate coefficients are obtained from a thorough review of the literature supplemented
by calculations of rates of important reactions when laboratory values are not available. Comparison of the model
with available observational constraints helps to determine the fundamental chemical pathways in the atmosphere.
We will discuss in particular the importance of recent measurements of HNC, HC15 N, CO2 , and H2 O and the role of
ion chemistry in the synthesis of neutral species. Key reactions that require further laboratory of theoretical study
will be identified.
TAC 2016
15 / 35
Tuesday
Tuesday 28, 16:25 - 16:45
Titan’s Temperature and Zonal Wind Structure and Seasonal Behavior
F. Flasar1 , Richard Achterberg2 and Paul Schinder3
1
2
University of Maryland
3
Cornell University
Titan’s atmosphere near 80 km (20 mbar) marks the transition between large radiative damping times at lower
altitudes, where seasonal variations are muted, and small damping times higher up, where temperatures and winds
vary significantly over the year. Cassini CIRS and Radio-Occultation measurements obtained in 2004-2016 have
tracked the evolution of temperatures and winds in Titan’s atmosphere from early northern winter to late spring. In
winter, the northern hemisphere was characterized by cold temperatures at high latitudes in the lower stratosphere
and a strong circumpolar vortex that extended to subtropical northern latitudes. At high altitudes over the north
pole, there was an elevated stratopause with a temperature roughly 30 K above the seasonal average, associated
with subsidence and adiabatic warming. As the northern hemisphere has moved toward summer the dissolution
of the circumpolar vortex has been gradual, and there is no evidence of rapid distortion and disruption forced by
planetary waves like that seen on Earth. During this time, the southern hemisphere has cooled fairly abruptly at high
latitudes. A circumpolar vortex has formed in the stratosphere, but it is more compact than seen in the north, with
maximum winds at 60°S. Potential vorticity maps now indicate steep meridional gradients at high southern latitudes,
implying a barrier to efficient mixing between the polar region and lower latitudes. One of the curious features of
Titan’s temperatures has been the destabilization seen in the winter north polar region, where negative temperature
gradients were observed between 80 and 100 km. As the southern hemisphere moves toward winter, temperatures
retrieved from radio occultation soundings have shown the early development this phenomenon at high southern
latitudes. The cause of the destabilization in winter may be associated with a cloud of organic ices. However, the
transition region near 80 km is also where the zonal winds exhibit a sharp minimum, first seen by the Huygens Probe
near 10°S, but later shown to exist globally from analysis of radio occultation soundings. The cause of this peculiar
behavior is not really understood, but it is reasonable that momentum damping of the zonal winds in the tropopause
region and lower stratosphere by breaking gravity waves may play a role.
Tuesday 28, 16:45 - 17:05
Cassini/CIRS results on Titan’s atmospheric properties changes since the northern equinox
Athena Coustenis1 , Don Jennings2 , Panayiotis Lavvas3 , Richard Achterberg2,4 , Georgios
Bampasidis5 , Conor Nixon2 , Gordon Bjoraker2 , F. Flasar2 and Nicholas Teanby6
1
2
3
4
5
6
LESIA, Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, Meudon Cedex, France
NASA/Goddard Space Flight Center, Greenbelt, USA
GSMA, Université de Reims, Reims, France
Department of Astronomy, University of Maryland, Maryland, USA
National and Kapodistrian University of Athens, Faculty of Phys., Astrophys., Astron. and Mech., Athens, Greece
School Earth Sci., Univ. Bristol, UK
Since 2010, we observe the onset and enhancement at Titan’s south pole of several trace species, such as HC3 N and
C6 H6 , observed only at high northern latitudes before equinox. We will present an analysis of spectra acquired by
Cassini/CIRS at high resolution mode since 2012 in nadir mode. We investigated several latitudes of 70°S to 70°N
since 2010 (after the Southern Autumnal Equinox) until end of 2014 [1-3]. For some of the most abundant and
longest-lived hydrocarbons (C2 H2 , C2 H6 and C3 H8 ) and CO2 , the evolution in the past 4 years at a given latitude
is not very significant within error bars especially until mid-2013 [1-4]. On the contrary, in the more recent dates,
these molecules show a dramatic trend for increase in the south. The 70°S and 50°S or mid-latitudes show different
behavior demonstrating that they are subject to different dynamical processes in and out of the polar vortex region.
For most species, we find higher abundances at 50°N compared to 50°S, with the exception of C3 H8 , CO2 , C6 H6 and
HC3 N, which arrive at similar mixing ratios after mid-2013 [3,4]. While the 70°N data show generally no change with
a trend rather to a small decrease for most species within 2014, the 70°S results indicate a strong enhancement in
trace stratospheric gases after 2012. In particular, HC3 N, HCN and C6 H6 have increased by 3 orders of magnitude
over the past 3-4 years while other molecules, including C2 H4 , C3 H4 and C4 H2 , have increased less sharply (by 1-2
orders of magnitude). This is a strong indication of the rapid and sudden buildup of the gaseous inventory in the
TAC 2016
16 / 35
Tuesday/Wednesday
southern stratosphere during 2013-2014, as expected as the pole moves deeper into winter shadow. Subsidence gases
that accumulate in the absence of ultraviolet sunlight, evidently increased quickly since 2012 and some of them may
be responsible also for the reported haze decrease in the north and its appearance in the south at the same time [5].
We also look for the build-up and appearance of condensate signatures in large averages of CIRS spectra, based on
model predictions.
References:
[1] Coustenis, et al., Icarus 207, 461, 2010 ;
[2] Bampasidis et al., ApJ 760, 144, 8 p., 2012.
[3] Coustenis et al., Astrophys. J. 799, 177, 9p, 2013 ;
[4] Coustenis, A., et al., Icarus 270, 409, 2016;
[5] Jennings, D. E., et al., ApJ Lett., 804, L34, 2015.
Wednesday 29, 09:00 - 09:20
Seasonal variations in Titan’s stratosphere observed with Cassini/CIRS after the
northern spring equinox
Sandrine Vinatier1 , Bruno Bézard1 , Nick Teanby2 , Sébastien Lebonnois3 , Rich Achterberg4 , Mike Flasar5 and The CIRS Team
1
LESIA, Observatoire de Paris-Meudon, France
School of Earth Science, University of Bristol, UK
3
LMD, University Paris 6, France
4
Department of Astronomy, University of Maryland, USA
2
5
NASA/GSFC, Greenbelt, USA
Since 2004, Cassini has made more than 116 Titan flybys, observing its atmosphere with instruments including
the Cassini Composite InfraRed Spectrometer (CIRS). We know from CIRS observations that the global dynamics
drastically changed after the northern spring equinox that occurred in August 2009 ([1-4]). The pole-to-pole middle atmosphere dynamics (above 100 km) experienced a global reversal in less than 2 years after the equinox [4],
while the northern hemisphere was entering spring. This new pattern, with downwelling at the south pole, resulted
in enrichment of almost all molecules inside the southern polar vortex, while a persistent enhancement due to the
former northern winter subsidence is still seen in the north pole region. According to General Circulation Model
calculations, this single circulation cell pattern should remain until 2025. We will present new 2015-2016 CIRS limb
observations analysis. We will show that many species (C2 H2 , HCN, HC3 N, C6 H6 , C4 H2 , CH3 CCH, C2 H4 ) are now
highly enriched near the south pole, by factors ∼100 at 500 km compared to just a few years ago. Such large middle
atmospheric enrichments were never observed before and are similar to in situ results from INMS at 1000 km [5]. We
will also show that the north pole displays for the first time since the beginning of the Cassini mission, a depletion
of molecular gas mixing ratios at altitudes higher than 300 km, while deeper levels remains enriched compared to
mid-latitude regions.
References:
[1] Teanby, N., et al., Nature, 491, pp. 733-735, 2012.
[2] Achterberg et al., DPS 46, abstract 102.07,Tucson, 2014.
[3] Coustenis et al., DPS 46, abstract 102.46, Tucson, 2014.
[4] Vinatier et al., Icarus, 250, 95-115, 2015.
[5] Cui et al., Icarus, 200, 581-615, 2009.
TAC 2016
17 / 35
Wednesday
Wednesday 29, 09:20 - 09:40
Seasonal variations of C4 H2 , C2 N2 and C3 H4 in Titan’s lower stratosphere
Melody Sylvestre1 , Nicholas Teanby1 and Patrick Irwin2
1
2
School of Earth Sciences, University of Bristol
Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory
Due to its obliquity (26.7°), Titan’s atmosphere undergoes significant seasonal variations of insolation, which are
expected to affect significantly its photochemistry and large-scale dynamics. The duration of the Cassini mission
enables us to monitor these changes and to better understand the atmospheric processes at play.
Here, we study the seasonal evolution of the composition of Titan’s lower stratosphere (10 mbar). We analyse
nadir high resolution (0.5 cm−1 ) spectra from Cassini/CIRS (Composite InfraRed Spectrometer) in the far infrared
(200-400 cm−1 ), in order to retrieve the abundances of three photochemical species: C2 N2 (cyanogen), C4 H2 (diacetylene), and C3 H4 (methylacetylene). These data span all the latitudes and were acquired from 2004 to 2015.
Consequently, they provide a good overview of the seasonal evolution of the meridional distributions of C2 N2 , C4 H2 ,
and C3 H4 , from northern winter to spring. For instance, these measurements show a strong enrichment in these three
species at the South pole in the lower stratosphere, consistent with previous observations (Coustenis et al., 2016 ;
Vinatier et al., 2015 ; Teanby et al., 2012). In contrast, other latitudes present much less variations in the mixing
ratios of these gases, especially at the North Pole. These measurements will be used to provide constraints on the
photochemistry and atmospheric dynamics in Titan’s lower stratosphere.
Wednesday 29, 09:40 - 10:00
Post-equinox evolution of Titan’s south-polar atmosphere
Nicholas Teanby1 , Sandrine Vinatier2 , Remco de Kok3 , Conor Nixon4 , Melody Sylvestre1
and Patrick Irwin5
1
University of Bristol
2
LEISA
SRON
4
GSFC
5
University of Oxford
3
Since northern spring equinox in mid-2009, Titan’s atmosphere has demonstrated dramatic changes in temperature
(Achterberg et al 2014), composition (Teanby et al 2012, Vinatier et al 2015, Coustenis et al 2016), and aerosol/ice
distribution (de Kok et al 2014, Jennings et al 2015, West et al 2016). The greatest changes have been at the southern
winter pole, which continues to enter deeper into Titan’s shadow. Observational highlights include development of a
south polar hot-spot, nitrile ice clouds, dense condensate clouds, and extreme trace gas concentrations.
Here we use recent infrared spectral limb observations by Cassini/CIRS to determine the evolution of temperature
and composition of the south polar region since equinox. Our observations show that the south polar hot-spot initially
observed following equinox has now disappeared and been replaced by extremely low temperatures throughout the
stratosphere, suspected to be due to enhanced radiative cooling. There also appears to be an unusual distribution of
nitrile species, which suggests trace gases are now escaping the newly formed winter vortex. Thus providing clues to
the underlying circulation. The new observations will be presented and implications for Titan’s polar atmospheric
dynamics discussed.
References:
Achterberg et al (2014), DPS46, 102.07, Tucson.
Coustenis et al (2016), Icarus, 270, 409-420.
de Kok et al (2014), Nature, 514, 65-67.
Jennings et al (2015), ApJL, 804, L34.
Teanby et al (2012), Nature, 491, 732-735.
Vinatier et al (2015), Icarus, 250, 95-115.
West et al (2016), Icarus, 270, 399-408.
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Wednesday
Wednesday 29, 10:00 - 10:20
The Abundance of C6 H6 and HC3 N over Titan’s South Pole as winter approaches
Gordon Bjoraker1 , Valeria Cottini2 , Richard Achterberg2 and Athena Coustenis3
1
2
NASA/GSFC
U. Maryland
3
Observatoire de Paris-Meudon
Benzene and cyanoacetylene have increased dramatically near Titan’s South Pole since 2011. First detected near the
South Pole in limb measurements, CIRS can now see strong emission lines of these species in nadir observations. This
is remarkable because at the same time stratospheric temperatures at the 1-mbar level (185 km) at 70°S have dropped
more than 30K in the past 5 years. CIRS obtained measurements of emission from these molecules as a function of
latitude during the T104 flyby on 2014 August 20. These data show the strongest emission at 83°S, falling off rapidly
towards 70°S. Recently, during T117 on 2016 February 16, CIRS obtained limb spectra at 80°S. These observations
show peak emission for C6 H6 between 200 and 250 km, while HC3 N peaks between 250 and 300 km (0.25 to 0.1
mbars) where the stratospheric temperature is near 160 K. These molecules are tracers of meridional transport in
Titan’s stratosphere and their confinement near the South Pole is reminiscent of the Antarctic ozone hole on Earth.
Wednesday 29, 11:00 - 11:20
Seasonal Evolution of Titan’s South Pole 220 cm−1 Cloud
Donald Jennings1
1
Goddard Space Flight Center
A cloud of ices that had been seen only in Titan’s north during winter began to emerge at the south pole in 2012.
Discovered by Voyager IRIS as an emission feature at 220 cm−1 , the cloud has been studied extensively in both the
north and south by Cassini CIRS. The spectral feature acts as a tracer of the seasonal changes at Titan’s poles,
relating to evolving composition, temperature structure and dynamics. Although candidates have been proposed,
the chemical makeup of the cloud has never been identified. The cloud is composed of condensates derived from
gases created at high altitude and transported to the cold, shadowed pole. In the north the cloud has diminished
gradually over the Cassini mission as Titan has transitioned from winter to spring. The southern cloud, on the other
hand, grew rapidly after 2012. By late 2014 it had developed a complex ring structure that was confined to latitudes
poleward of 70°S within the deep temperature well that had formed at the south pole [1]. The location of the cloud
coincides in latitude with the HCN cloud reported by ISS and VIMS [2,3]. CIRS also saw enhanced gas emissions at
those latitudes [4]. When it first formed, the cloud was abundant at altitudes as high as 250 km, while later it was
found mostly at 100-150 km, suggesting that the material that had been deposited from above had gathered at the
lower altitudes. Radiance from the southern cloud increased until mid-2015 and since then has decreased. The cloud
may be transitioning to the more uniform hood morphology familiar in the north. Taking the north and south together, by the end of the Cassini mission in 2017 we will have observed almost an entire seasonal cycle of the ice cloud.
References:
[1] Jennings, D. E., et al., ApJ Lett., 804, L34 (2015).
[2] West, R. A., et al., DOI10.1016/j.icarus.2014.11.038 (2014).
[3] de Kok, R. et al., Nature, 514, 65, (2014).
[4] Coustenis, A., et al., Icarus 270, 409 (2016).
TAC 2016
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CH4 cycle (surface, clouds and rains) and Climate
Wednesday
Abstracts: CH4 cycle (surface, clouds and rains) and Climate
Conveners: S. Rafkin and C. Sotin
Wednesday 29, 13:45 - 14:05
Mapping Methane in Titan’s Atmosphere near Titan’s Surface
Eliot Young1 , Jason Soderblom2 and Jason Barnes3
1
Southwest Research Institute
Massachusetts Institute of Technology
3
University of Idaho
2
Titan’s atmospheric methane may be coupled to sources and sinks on its surface. In order to map methane concentrations in layers just above Titan’s surface, we use data sets in which locations on Titan are imaged from a variety
of viewing angles (and within a short time span). We also use a radiative transfer code based on the Markov Chain
method of Esposito and House (1978, AJ 219, 1058) to accommodate spherical atmospheric geometries. We report
on (a) selected Cassini/VIMS flybys that image terrain on Titan from different angles, (b) the expected vertical
resolution of methane maps near the surface from these flybys and (c) preliminary results: 3D methane and haze
distributions and surface albedos.
Wednesday 29, 14:05 - 14:25
Constraining and Interpreting Titan’s Methane Hydrologic Cycle
Juan Lora1 , Jonathan Mitchell1 and Mate Adamkovics2
1
2
UCLA
UC Berkeley
Titan’s surface supports large reservoirs of stable hydrocarbon liquids, while active weather and a seasonal cycle
operate in the troposphere. Titan’s hydrologic cycle transports methane between the atmosphere, the surface, and,
potentially, the sub-surface on various timescales. Yet the detailed distribution of methane both in the lower atmosphere and in the surface is essentially unknown, though studies of the processes that control it, from seasonal to
orbital timescales, are now relatively mature. Many conundrums remain regarding observed hydrologic phenomena.
For example, why have widely-expected cloud outbursts at the North pole failed to materialize? Why are there
extensive fluvial surface features at the dry low latitudes? Using a combination of general circulation, radiative
transfer, and surface modeling, in conjunction with ground-based and Cassini observations, we are working to better
characterize and predict tropospheric cloud occurrence, measure and interpret the variability of lower-atmosphere
humidity, and clarify the distribution of lakes and surface features and their connection to the atmosphere. Within
this context, I will summarize our efforts to improve our understanding of the atmospheric circulation, dynamics, and
surface-atmosphere interactions that affect the hydrologic cycle, to gain a better insight into Titan’s climate system
and its evolution.
Wednesday 29, 14:25 - 14:45
Cloud formation in Titan’s Stratosphere
Erika Barth1
1
In addition to the organic haze particles produced photochemically in Titan’s upper atmosphere, a number of trace
gases are also created. These hydrocarbon and nitrile species include C2 H6 , C2 H2 , C4 H10 , HCN, HC3 N, C2 H5 CN
and many more. While both Voyager and Cassini observations have found evidence for ices (e.g. C4 N2 , HCN) in the
atmosphere above Titan’s poles, these species are also likely to condense at other latitudes forming optically thin ice
layers in the stratosphere. A series of simulations have been conducted using Titan CARMA, a 1-D microphysics
and radiative transfer model, to explore cloud particle formation with ∼20 of Titan’s trace hydrocarbon and nitrile
gases. These species reach their condensation temperatures between 60 and 110 km. Most condense solely as ices,
however, C3 H8 will condense first near 70 km as a liquid and then freeze as the droplets descend toward the surface.
C3 H8 and C2 H6 join CH4 as a liquid at Titan’s surface. Many ices have long condensation timescales resulting
in particle radii ∼1 micron or less. Several (including HCN, C3 H8 , C2 H2 ) will grow 10-50 times larger. Expected
TAC 2016
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Wednesday
condensation altitudes and particle sizes will be presented, as well as the implications for the optical properties of
Titan’s stratospheric aerosol particles.
Wednesday 29, 14:45 - 15:05
Towards More Realistic Simulation of Air-Sea Interaction over Lakes on Titan
Scot Rafkin1 and Alejandro Soto1
1
The exchange of methane between the atmosphere and surface liquid reservoirs dominates the short time-scale
methanological cycle. In this study, previous two-dimensional simulations of the exchange of methane vapor, sensible heat and momentum between the atmosphere and lakes are updated with the inclusion of radiative forcing and
extended to three dimensions, including the introduction of realistic coastlines. Previous studies of Titan’s air-sea
exchange in two dimensions suggested that the exchange process was self-limiting. Evaporation from lakes produced
a shallow but extremely stable marine layer that suppressed turbulent exchange. Furthermore, the circulation associated with the higher buoyancy of methane-rich atmosphere over the lake was offset by the oppositely directed
thermal sea breeze circulation, which muted the mean wind. Two major weaknesses of this previous work were the
lack of radiative forcing and the imposition of two dimensionality that limited the full range of dynamical solutions.
Based on early theoretical studies, it was thought that magnitude of turbulent energy flux exchanges would be much
larger than radiative fluxes, thereby justifying the neglect of radiation, but the two-dimensional simulations indicated
that this was not a valid assumption. The dynamical limitations of two-dimensional simulations are well known.
Vorticity stretching (i.e., circulation intensification through vertical motion) is not possible and it is also not possible
to produce dynamically balanced gradient wind-type circulations. As well, the irregular shape of a realistic coastline
cannot be expressed in two dimensions, and these realistic structures will generally induce complex convergence and
divergence circulations in the atmosphere. The impact of radiative forcing and the addition of the third dimension
on the air-sea exchange are presented.
Wednesday 29, 15:45 - 16:05
How often does it rain on Titan? (And what happens when it does?)
Ralph Lorenz1
1
JHU Applied Physics Laboratory
Titan precipitation indicated by global circulation models may be several m/yr at the poles, but much less at the
equator. This amount is rather higher than the few cm/yr estimated pre-Cassini from globally-averaged radiative
fluxes and reflects the strong seasonal modulation of the surface energy balance. Although the poles evidently receive
more precipitation overall, accounting in part for the observed distribution of lakes and seas at high latitude and
dune-covered deserts at low latitudes, it was immediately obvious from the Huygens DISR images (and subsequent
Cassini radar observations) that river channels do form at the equator. However, the rarity of dunes cut by river
channels confirms that storms must be relatively rare.
Mesoscale models indicate that many tens of cm of rain can fall in an individual storm cell (with a rain shaft
diameter comparable with the atmospheric scale height) over a few hours. These basic properties guide an overall
perspective on ’what the weather is like’, useful both for estimating rates of geomorphological change, as well as
spacecraft mission planning.
The amount of precipitation delivered over a given area by a given event also drives Titan’s transient hydrology
- like many terrestrial deserts, there are abundant river valleys, but most are dry most of the time. The duration of
flow can be estimated as a function of catchment area, bed roughness, width and slope etc.
An important additional effect of the latitude gradient in precipitation is the possible forcing of a compositional
distinction between the northernmost seas Punga and Ligeia, and Kraken which sprawls towards the warmer, dryer
equator. This ’Flushing of Ligeia’ scenario, like the Black Sea and Mediterranean, remains to be confirmed by observations, and depends on the hydraulic connection between the seas (Trevize Fretum). The strong seasonal cycle in
precipitation may lead to a seasonal composition variation, and indeed a change in the sea level in, Ligeia Mare.
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Wednesday
Wednesday 29, 16:05 - 16:25
Likelihood of nitrogen condensation in Titan’s present atmosphere
Tetsuya Tokano1
1
Institut für Geophysik und Meteorologie, Universität zu Köln
Nitrogen condensation is considered to have taken place in Titan’s atmosphere in the past when the atmosphere
contained much less methane than today or the solar luminosity was smaller. On the other hand, it is not known
for sure whether nitrogen condensation takes place on present-day Titan. Vertical temperature profiles in Titan’s
troposphere obtained Voyager, Huygens and Cassini do not reach the pressure-dependent nitrogen condensation
temperature at any location, so that nitrogen condensation was probably not occurring along these profiles at the
time of measurements. However, these spacecraft may not have sounded the coldest seasons and areas of Titan
since they all took place in the seasons following perihelion. The seasonal cycle of temperature and nitrogen relative
humidity in Titan’s troposphere has been simulated by a general circulation model in an effort to explore possible
areas and seasons of nitrogen condensation on present Titan. In contrast to the upper stratosphere, the seasonal
temperature variation in the troposphere is more strongly controlled by Saturn’s orbital eccentricity than by Saturn’s
obliquity. Consequently, the tropospheric temperature globally decreases between the northern vernal equinox and
autumnal equinox and reaches the annual minimum around the northern autumnal equinox approximately one season
after aphelion. It is possible if not certain that the polar atmosphere between 30 and 40 km altitude temporarily
reach the nitrogen condensation temperature in this season and thereby causes liquid nitrogen clouds. Qualitative
differences to the more common methane condensation as well as possible impact on Titan’s weather are discussed.
Wednesday 29, 16:25 - 16:45
Paleoclimates on Titan: the case of a pure nitrogen atmosphere
Benjamin Charnay1 , François Forget2 , Gabriel Tobie3 , Christophe Sotin4 and Robin Wordsworth5
1
University of Washington
LMD
3
LPGN
2
4
5
JPL
Harvard University
Several clues indicate that Titan’s atmosphere has been depleted in methane during some period of its history, possibly as recently as 0.5–1 billion years ago. It could also happen in the future. Under these conditions, the atmosphere
becomes only composed of nitrogen with a range of temperature and pressure allowing liquid or solid nitrogen to
condense. We explored these exotic climates throughout Titan’s history with a 3D Global Climate Model (GCM)
including the nitrogen cycle and the radiative effect of nitrogen clouds (Charnay et al. 2014). We found that for
the last billion years, only small polar nitrogen lakes should have formed. Yet, before 1 Ga, a significant part of
the atmosphere could have condensed, forming deep nitrogen polar seas, which could have flowed and flooded the
equatorial regions. During this talk, I will present our results and discuss the possible implications for the erosion
and the age of Titan’s surface, for the flattening of the polar regions and for the methane outgassing on Titan.
References:
Charnay et al. (2014), Icarus
TAC 2016
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Posters
Monday
Posters session
Poster 1
Global frequency and intensity analysis of the ν10 /ν7 /ν4 /ν12 band system of
at 10 µm using the D2h Top Data System
12
C2 H4
Abdulsamee Alkadrou1 , Marie-Thérèse Bourgeois1 , Maud Rotger1 , Vincent Boudon1
and Jean Vander Auwera1
1
GSMA - Université de Reims Champagne-Ardenne
A global frequency and intensity analysis of the infrared tetrad of 12C2 H4 located in the 600-1500 cm−1 region
was carried out using the tensorial formalism developed in Dijon for X2 Y4 asymmetric-top molecules. It relies on
spectroscopic information available in the literature and retrieved from high-resolution Fourier transform infrared
spectra recorded in Brussels in the frame of either the present or previous work. In particular, 645 and 131 lines
intensities have been respectively measured for the weak ν10 and ν4 bands. Including the Coriolis interactions affecting
the upper vibrational levels 101 , 71 , 41 and 121 , a total of 10,737 line positions and 1,867 line intensities have been
assigned and fitted with global root mean square deviations of 2.6 10−4 cm−1 and 2.4 %, respectively. Relying on
the results of the present work and available in the literature, a list of parameters for 65,420 lines in the ν10 , ν7 , ν4
and ν12 bands of 12C2 H4 was generated. To the best of our knowledge, this is the first time that a global intensity
analysis is carried out in this range of the ethylene spectrum.
Poster 2
Ab initio calculations of low temperature hydrocarbon spectra for astrophysics:
application to the modeling of methane absorption in the Titan atmosphere in
a wide IR range
Michael Rey1 , Andrei Nikitin2 , Bruno Bézard3 , Pascal Rannou1 , Athena Coustenis3 and
Vladimir Tyuterev1
1
GSMA - Université de Reims Champagne-Ardenne, France
Institute of Atmospheric Optics SB, Russian Academy of Sciences, Tomsk, Russia
3
LESIA, Observatoire de Paris, Meudon, France
2
Knowledge of intensities of spectral transitions in various temperature ranges including very low-T conditions is essential for the modeling of optical properties of planetary atmospheres and for other astrophysical applications. The
temperature dependence of spectral features is crucial, but quantified experimental information in a wide spectral
range is generally missing. A significant progress has been recently achieved in first principles quantum mechanical
predictions (ab initio electronic structure + variational nuclear motion calculations) of rotationally resolved spectra
for hydrocarbon molecules such as methane , ethylene and their isotopic species [1,2] . We have recently reported the
TheoReTS information system (theorets.univ-reims.fr, theorets.tsu.ru) for theoretical spectra based on variational
predictions from molecular potential energy and dipole moment surfaces [3] that permits online simulation of radiative
properties including low-T conditions of cold planets. In this work, we apply ab initio predictions of the spectra of
methane isotopologues down to T=80 K for the modeling of the transmittance in the atmosphere of Titan, Saturn’s
largest satellite explored by the Cassini-Huygens space mission. A very good agreement over the whole infrared
range from 6,000 to 11,000 cm−1 compared with observations obtained by the Descent Imager / Spectral Radiometer
(DISR) on the Huygens probe [4,5] at various altitudes will be reported.
References:
[1] M. Rey, A.V. Nikitin and Vl. G. Tyuterev, Phys. Chem. Chem. Phys., 15, 10049 (2013); J. Chem. Phys., 141 (2014) 044316;
J.Mol.Spectrosc. 291, 85 (2013).
[2] T. Delahaye, A. Nikitin, M. Rey, P. Szalay, V.Tyuterev, Chem.Phys.Lett. 639, 275 (2015)
[3] M. Rey, A.Nikitin, Yu.Babikov and V. Tyuterev, J.Mol.Spectrosc. , April 2016 doi:10.1016/j.jms.2016.04.006
[4] M. Tomasko, et al., Nature 438, 765-778 (2005)
[5] B. Bézard , Icarus 242, 64-73 (2014)
TAC 2016
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Posters
Monday
Poster 3
Anion-molecule reactions in Titan’s atmsophere: a laboratory perspective
Ludovic Biennier1 , Baptiste Joalland1 , Nour Jamal-Eddine1 , Sophie Carles1 , Jean-Claude
Guillemin2 and Yann Trolez2
1
Institut de Physique de Rennes
2
Ecole Nationale Supérieure de Chimie de Rennes
Heavy ions discovered in the upper atmosphere of Titan may play some role in the production of aerosols observed at
lower altitudes. The composition of the large ions and molecules found in the ionosphere, and their precise formation
mechanisms are still largely unknown. This lack of information includes the first steps leading to the production of
these species, which govern the growth rate. In particular, negative ion cold chemistry has not been explored systematically. There have been a number of experimental studies conducted to determine the kinetics of anion-neutral
reactions, but a fraction only has simultaneously led to the determination of the nature of products and even less to
the branching ratio into the different exit channels.
In the laboratory, we recently engaged in kinetics studies of anion-molecule reactions starting with the reaction of
CN– and C3 N– with cyanoacetylene HC3 N over the 50-300 K temperature range using the CRESU technique (French
acronym standing for Reaction Kinetics in Uniform Supersonic Flow). The results show that the CN– + HC3 N
reaction contributes directly to the growth of larger anions whereas CN– + HC3 N does not. The investigation was
recently extended in the laboratory to larger ions and other polar co-reactants. The development of a versatile
selected anion source, to be combined with the CRESU apparatus, will be also presented.
Poster 4
Investigating the first steps of hydrocarbon condensation in the laboratory and
in Titan’s atmosphere
Ludovic Biennier, Jérémy Bourgalais1 , Abdessamad Benidar1 and Sébastien Le Picard1
1
Hydrocarbons formed in Titan's cold atmosphere, starting with ethane C2 H6 , ethylene C2 H4 , acetylene C2 H2 , propane
C3 H8 ,... up to benzene C6 H6 , play some role in aerosol production, cloud processes, rain generation and Titan's lakes
formation.
We have started to study in the laboratory the kinetics of the first steps of condensation of these hydrocarbons.
Rate coefficients are very sensitive to the description of the potential interaction surfaces of the molecules involved.
Combined theoretical and experimental studies at the molecular level of the homogenous nucleation of various small
molecules should improve greatly our fundamental understanding. This knowledge will serve as a model for studying
more complex nucleation processes actually taking places in planetary atmospheres.
Here we present the first experimental kinetic study of the dimerization of two small hydrocarbons: ethane C2 H6 and
propane C3 H8 . We have performed experiments to identify the temperature and partial densities ranges over which
small hydrocarbon clusters form in saturated uniform supersonic flows. Using our unique reactor based on a Laval
nozzle expansions, the kinetics of the formation has also been investigated down to 23 K. The chemical species present
in the reactor are probed by a time of flight mass spectrometer equipped with an electron gun for soft ionization of
the neutral reagents and products.
This work aims at putting some constraints on the role of small hydrocarbon condensation in the formation of
haze particles in the dense atmosphere of Titan.
Poster 5
Day to night ion transport flow and its variation with SLT
Yingjuan Ma1 and Andy, F. Nagy2
1
UCLA
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24 / 35
Posters
2
Monday
University of Michigan
In this presentation, we will examine the day to night ion transport flow at Titan based on 3D MHD model results.
As this flow is influenced by the relative direction of the upstream co-rotation plasma flow as Titan moved along its
orbit, we will present and compare the day-to-night ion transport flow at four different SLTs.
Poster 6
Influence of traces elements in the organic chemistry of upper atmosphere of
Titan
Christophe Mathé1 , Nathalie Carrasco1 , Melissa, G. Trainer2 , Thomas Gautier3 , Lisseth Gavilan1 , David Dubois1 and Xiang Li4
1
LATMOS
NASA-GSFC
3
Center for Space Science and Technology, Universities Space Research Association, USRA
4
Center for Space Science and Technology, University of Maryland,Baltimore County
2
In the upper atmosphere of Titan, complex chemistry leads to the formation of organic aerosols. Since the work
of Khare et al. in 1984, several experiments investigated the formation of Titan aerosols, so called tholins, in the
laboratory. It has been suggested that nitrogen-containing compounds may contribute significantly to the aerosols
formation process. In this study, we focused on the influence of pyridine, the simplest nitrogenous aromatic hydrocarbon, on the chemistry of Titan's atmosphere and on aerosol formation.
To assess the effect of pyridine on aerosol formation chemistry, we used two different experimental setups : a capacitively coupled radio-frequency (electronic impact), and a VUV Deuterium lamp (photochemistry) in a collaboration
between LATMOS (Guyancourt) and NASA-GSFC (Greenbelt), respectively. Aerosols produced with both setups
were first analyzed using a FTIR-ATR (Fourier Transform Infrared spectroscopy - Attenuated Total Reflection) with
a spectral range of 4000-800 cm−1 to characterize their optical properties. Next the samples were analysed using a
Bruker Autoflex Speed MALDI mass spectrometer with a m/z range up to 2000 Da in order to infer their composition.
Infrared spectroscopy analysis showed that tholins produced with a nitrogen-methane gas mixture (95:5) and nitrogenpyridine gas mixture (99:250ppm) present very similar spectra features. Tholins produced with a mixture of nitrogenmethane-pyridine (99:1:250ppm) do not present aliphatic CH2 or CH3 vibrational signatures. This could indicate a
cyclic polymerization by a pyridine skeleton. Mass spectrometry is still in progress to confirm this.
Poster 7
Could PAH or HAC explain the Titan’s stratosphere absorption around 3.4 µm
revealed by solar occultations?
Daniel Cordier1 , Thibaud Cours1 , Michael Rey1 , Luca Maltagliati2 , Benoît Seignovert1
and Ludovic Biennier3
1
GSMA - Université Reims Champagne Ardenne, Reims, FR
LESIA-Observatoire de Paris
3
2
In 2006, during Cassini's 10th flyby of Titan (T10), Bellucci et al. (2009) observed a solar occultation by Titan’s
atmosphere through the solar port of the Cassini/VIMS instrument. These authors noticed the existence of an unexplained additional absorption superimposed to the CH4 3.3 µm band. Because they were unable to model this
absorption with gases, they attributed this intriguing feature to the signature of solid state organic components. Kim
et al. (2011) revisited the data collected by Bellucci et al. (2009) and they considered the possible contribution of
aerosols formed by hydrocarbon ices. They specifically took into account C2 H6 , CH4 , CH3 CN, C5 H12 and C6 H12
ices. More recently, Maltagliati et al. (2015) analyzed a set of four VIMS solar occultations, corresponding to flybys
performed between January 2006 and September 2011 at different latitudes. They confirmed the presence of the
3.3 µm absorption in all occultations and underlined the possible importance of gaseous ethane, which has a strong
plateau of absorption lines in that wavelength range.
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Posters
Monday
In this work, we show that neither hydrocarbon ices nor molecular C2 H6 cannot satisfactorily explain the observed
absorption. Our simulations speak in favor of an absorption due to the presence of PAH molecules or HAC in the
stratosphere of Titan. PAH have been already considered by Lopes-Puertas et al. (2013) at altitudes larger than ∼900
km and tentatively identified in the stratosphere by Maltagliati et al. (2015); PAH and HAC are good candidates for
Titan’s aerosols precursors.
Poster 8
ALMA observations of Titan : Vertical and spatial distributions of nitriles
Raphael Moreno1 , Emmanuel Lellouch1 , Sandrine Vinatier1 , Mark Gurwell2 , Arielle
Moullet3 , Luisa Lara4 and Taufiq Hidayat5
1
Observatoire de Paris-Meudon
Harvard-Smithsonian CfA
3
NRAO
4
IAA-CSIC
2
5
Bandung observatory
We report submm observations of Titan performed with the ALMA interferometer centered at the rotational frequencies of HCN(4-3) and HNC(4-3), i.e. 354 and 362 GHz. These measurements yielded disk-resolved emission spectra of
Titan with an angular resolution of ∼0.47”. Titan’s angular surface diameter was 0.77”. Data were acquired in summer 2012 near the greatest eastern and western elongations of Titan at a spectral resolution of 122 kHz (λ/dλ = 3106).
We will present radiative transfer analysis of the acquired spectra. With the combination of all the detected rotational lines, we will constrain the atmospheric temperature, the spatial and vertical distribution HCN, HC3 N,
CH3 CN, HNC, C2 H5 CN, as well as isotopic ratios.
Poster 9
Isotopic Ratios of Carbon and Oxygen in Titan’s CO using ALMA
Joseph Serigano1 , Conor, A. Nixon2 , Martin, A. Cordiner2 , Patrick, G. J. Irwin3 , Nick,
A. Teanby4 , Steven, B. Charnley2 and Johan, E. Lindberg2
1
2
3
4
University of Oxford
The advent of the Atacama Large Millimeter/Submillimeter Array (ALMA) has provided a new and powerful facility
for probing the atmospheres of solar system targets at long wavelengths (84-720 GHz) where the rotational lines of
small, polar molecules are prominent. In the complex atmosphere of Titan, photochemical processes dissociate and
ionize molecular nitrogen and methane in the upper atmosphere, creating a complex inventory of trace hydrocarbons
and nitriles. Additionally, the existence of oxygen on Titan facilitates the synthesis of molecules of potential astrobiological importance.
Utilization of ground-based submillimeter observations of Titan has proven to be a powerful tool to complement
results from spacecraft observations. ALMA provides the ability to probe this region in greater detail with unprecedented spectral and spatial resolution at high sensitivity, allowing for the derivation of vertical mixing profiles,
molecular detections, and observations of latitudinal and seasonal variations. Recent ALMA studies of Titan have
presented spectrally and spatially-resolved maps of HNC and HC3 N emission (Cordiner et al. 2014), as well as the
first spectroscopic detection of ethyl cyanide (C2 H5 CN) in Titan’s atmosphere (Cordiner et al. 2015).
This poster will focus on ALMA observations of carbon monoxide (CO) and its isotopologues 13CO, C18 O, and
C17 O in Titan’s atmosphere. Molecular abundances and the vertical atmospheric temperature profile were derived
by modeling the observed emission line profiles using NEMESIS, a line-by-line radiative transfer code (Irwin et al.
2008). This study reports the first spectroscopic detection of 17O in the outer solar system with C17 O detected at
>8σ confidence. The abundances of these molecules and isotopic ratios of 12C/ 13C, 16O/ 18O, and 16O/ 17O will be
presented. General implications for the history of Titan from these measurements will be discussed.
TAC 2016
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Posters
Monday
Poster 10
Explaining the high electron density observed during T57
Darci Snowden1 , Mike Smith1 and Theo Jimson1
1
RPWS observed abnormally high electron densities on the solar limb of Titan’s atmosphere during T57 and several
other flybys. We show that ion precipitation likely provided the additional ionization needed to explain the T57 data.
To show this we use a 3D model of Titan’s interaction with Saturn’s magnetosphere to simulate the magnetic and
electric fields near Titan. Then we use a particle tracing code to calculate the global energy flux of ions onto Titan’s
exobase. Finally, we calculate the energy deposition rates and ionization rates of the ions as they penetrate Titan’s
atmosphere.
Poster 11
Simulating the VUV photochemistry in the upper atmosphere of Titan
Sarah Tigrine1,2 , Nathalie Carrasco1 , Ludovic Vettier1 and Guy Cernogora1
1
2
Synchrotron SOLEIL
LATMOS
The Cassini mission around Titan revealed that the interaction between the N2 and CH4 molecules and the solar VUV
radiation leads to a complex chemistry above an altitude of 800 km with the detection of heavy organic molecules
like benzene (C6 H6 ). This is consistent with an initiation of the aerosols in Titan’s upper atmosphere. The presence
of those molecules makes Titan a natural laboratory to witness and understand prebiotic-like chemistry but despite
all the data collected, all the possible photochemical processes in such a hydrocarbon-nitrogen-rich environment are
not precisely understood.
This is why Titan’s atmospheric chemistry experiments are of high interest, especially those focusing on the photochemistry as most of the Titan-like experiments are based on N2 -CH4 plasma techniques. In order to reproduce this
VUV photochemistry of N2 and CH4 , we designed a photochemical reactor named APSIS which is to be coupled
window-less with a VUV photon source as N2 needs wavelengths shorter than 100 nm in order to be dissociated.
Those wavelengths are available at synchrotron beamlines but are challenging to obtain with common laboratory discharge lamps. At LATMOS, we developed a table-top VUV window-less source using noble gases for the micro-wave
discharge. We started with Neon, as it has two resonance lines at 73.6 and 74.3 nm which allow us to dissociate
and/or ionize both CH4 and N2 .
We will present here our first experimental results obtained with APSIS coupled with this VUV source and then
discuss them regarding the Cassini data and other previous laboratory photochemical studies.
Poster 12
Nitrile and Hydrocarbon Spatial Abundance Variations in Titan’s Atmosphere
Alexander, E. Thelen1 , Conor, A. Nixon2 , Edward Molter2 , Joseph Serigano3 , Martin,
A. Cordiner2 , Steven, B. Charnley2 , Nick Teanby4 and Nancy Chanover1
1
New Mexico State University
2
4
3
Many minor constituents of Titan’s atmosphere exhibit latitudinal variations in abundance as a result of atmospheric
circulation, photochemical production and subsequent destruction throughout Titan’s seasonal cycle [1,2]. Species
with observed spatial abundance variations include hydrocarbons - such as CH3 CCH - and nitriles - HCN, HC3 N,
CH3 CN, and C2 H5 CN - as found by Cassini [3,4]. Recent calibration images of Titan taken by the Atacama Large
Millimeter/Submillimeter Array (ALMA) allow for measurements of rotational transition lines of these species in
spatially resolved regions of Titan’s disk [5]. Abundance profiles in Titan’s lower/middle atmosphere are retrieved
by modeling high resolution ALMA spectra using the Non-linear Optimal Estimator for MultivariatE Spectral analySIS (NEMESIS) radiative transfer code [6]. We present continuous abundance profiles for various species in Titan’s
TAC 2016
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Posters
Monday
atmosphere obtained from ALMA data in 2014. These species show polar abundance enhancements which can be
compared to studies using Cassini data [7]. Measurements in the mesosphere will constrain molecular photochemical
and dynamical models, while temporal variations inform our knowledge of chemical lifetimes for the large inventory
of organic species produced in Titan’s atmosphere. The synthesis of the ALMA and Cassini datasets thus allow us to
observe the important changes in production and circulation of numerous trace components of Titan’s atmosphere,
which are attributed to Titan’s seasons.
References:
[1] Coustenis, A., Jennings, D. E., Nixon, C. A., et al. 2010, Icarus, 207, 461
[2] Cordiner, M. A., Nixon, C. A., Teanby, N. A., et al. 2014, ApJ, 795, L30
[3] Teanby, N. A., Irwin, P. G. J., de Kok, R., et al. 2007, Icarus, 186, 364
[4] Vinatier, S., Bézard, B., Fouchet, T., et al. 2007, Icarus, 188, 120
[5] Cordiner, M. A., Palmer, M. Y., Nixon, C. A., et al. 2015, ApJ, 800, L14
[6] Irwin, P. G. J., Teanby, N. A., de Kok, R., et al. 2008, JQSRT, 109, 1136
[7] Teanby, N. A., Irwin, P. G. J., Nixon, C. A., et al. 2013, Planetary & Space Sci., 75, 136
Poster 13
Large-scale simultaneous mapping of Titan’s aerosol opacity and surface albedo
by a new massive inversion method of Cassini/VIMS data
Luca Maltagliati1,2 , Sébastien Rodriguez1,3 , Christophe Sotin4,5 , Pascal Rannou6 , Bruno
Bézard2 , Anezina Solomonidou4 , Athena Coustenis2 , Thomas Apperé1 , Thomas Cornet7
and Stéphane Le Mouélic5
1
2
3
4
5
6
7
AIM CEA Saclay
LESIA Observatoire de Paris
Université Paris 7
JPL
LPG Nantes
GSMA Reims
ESAC/ESA
We have still limited information on Titan’s surface albedo in the near-infrared. Only few spectral windows exist
in between the intense methane bands, and even those windows are strongly affected by atmospheric contributions
(absorption, scattering). Yet, this part of the spectrum is important to determine the surface composition thanks
to the wealth of absorption bands by minerals and ices present there. A radiative transfer model is an effective
tool to take the atmospheric effects into consideration in the analysis (e.g. Rannou et al. 2010, Griffith et al 2012,
Solomonidou et al. 2016,...), but it is too time-consuming to process the whole VIMS hyperspectral dataset (millions
of spectra) and create large-scale maps of the surface albedo.
To overcome this problem, we developed an inversion method of VIMS data that employs lookup tables of synthetic
spectra produced by a state-of-the-art radiative transfer model (described in its original form in Hirtzig et al. 2013).
The heavy computational part (calling the radiative transfer model) is thus done only once for all during the creation
of the modeled spectra. We updated the model with new methane spectroscopy and the new aerosol parameters
we found in our analysis of the VIMS Emission Phase Function (see the other Maltagliati et al. abstract in this
workshop). We analyzed in detail the behavior of the spectra as a function of the free parameters of the model
(three inputs, the incidence, emergence and azimuth angles; and two products: the aerosol opacity and the surface
albedo) in order to create an optimized grid for the lookup table. The lookup tables were then grafted onto an ad-hoc
inversion model.
Our method can process a whole 64x64 VIMS datacube in few minutes, with a gain in computational time of a
factor of more than one thousand with respect to the standard method. This will consent for the first time a truly
massive inversion of VIMS data and large-scale acquisition of Titan’s surface albedo, paving the way for global maps
of mineralogical composition (and related temporal variations). Results of simultaneous maps of aerosol opacity
and surface albedo for the various surface windows are shown for some selected flybys observing the same area with
different geometries, to highlight the robustness of the method to correct seamlessly the atmospheric effects.
TAC 2016
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Posters
Monday
Poster 14
Explorer of Enceladus and Titan (E2T)
Giuseppe Mitri1 , Gabriel Tobie1 , Frank Postberg2 , Jason , M. Soderblom3 , Peter Wurz4 ,
Jason , W. Barnes5 , Marco Berga6 , Athena Coustenis7 , Andrea d’Ottavio8 , Alexander, G. Hayes9 , Paul, O. Hayne10 , Jean-Pierre Lebreton11 , Ralph , D. Lorenz12 , Andrea
Martelli8 , Anastassios , E. Petropoulos10 , Chen-wan, L. Yen10 , Kim, R. Reh10 , Christophe
Sotin10 , Ralf Srama13 and Paolo Tortora14
1
University of Nantes
University of Heidelberg
3
Massachusetts Institute of Technology
4
University of Bern
5
University of Idaho
2
6
Thales Alenia Space
LESIA, Observatoire de Paris
8
Thales Alenia Space
9
Cornell University
10
Jet Propulsion Laboratory
11
LPC2E
7
12
JHU Applied Physics Laboratory
University of Stuttgart
14
13
The NASA-ESA Cassini-Huygens mission has revealed Titan and Enceladus to be two of the most enigmatic worlds
in the Solar System. Titan, with its organically rich and dynamic atmosphere and geology, and Enceladus, with its
active plume, both harboring subsurface oceans, are prime environments in which to investigate the conditions for
the emergence of life and the habitability of Ocean Worlds. Explorer of Enceladus and Titan (E2T) is dedicated
to investigating the evolution and habitability of these Saturnian satellites and will be proposed as a medium-class
mission led by ESA in collaboration with NASA in response to ESA’s M5 Call. E2T has a focused payload that
will provide in-situ sampling and high-resolution imaging during multiple flybys of Enceladus and Titan using a
solar-electric powered spacecraft in orbit around Saturn. The E2T mission will provide high-resolution mass spectroscopy of the plume emanating from Enceladus’ south polar terrain (SPT) and of Titan’s upper atmosphere as well
as high-resolution IR imaging of the plume and the source fractures on Enceladus’ SPT, and it will detail Titan’s
geomorphology at 50-100 m resolution. The E2T mission has three scientific goals: 1) Investigate the origin and
evolution of volatile-rich icy worlds by examining both Enceladus and Titan, 2) Investigate the habitability and
potential for life in ocean worlds on both Enceladus and Titan and 3) Investigate Titan as an Earth-like world with
an evolving climate and landscape. These investigations will be accomplished by measuring the nature, abundance
and isotopic properties of solid- and vapor-phase species in Enceladus’ plume and Titan’s upper atmosphere. E2T’s
high-resolution time-of-flight mass spectrometers will enable us to untangle the ambiguities left by Cassini regarding
the identification of low-mass organic species, identify high-mass organic species for the first time, further constrain
trace species such as the noble gases, and clarify the evolution of solid and volatile species. High-resolution IR imaging
will reveal Titan’s surface and Enceladus’s fractured SPT and plume in detail unattainable by the Cassini mission,
allowing us to investigate the processes that are transporting and transforming organic materials on the surface of
Titan, and constrain the mechanisms controlling, and the energy dissipated by, Enceladus’ plume. The proposed
mission will address key scientific questions regarding extraterrestrial habitability, abiotic/prebiotic chemistry and
emergence of life, which are among the highest priorities of ESA’s Cosmic Vision program.
TAC 2016
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Posters
Monday
Poster 15
Exploring the Composition of Titan’s Lakes through Laboratory Experiments
Jennifer Hanley1 , Garrett Thompson2 , Henry Roe1 and Will Grundy1
1
2
Lowell Observatory
Northern Arizona University
Previous studies have shown that the lakes of Titan are composed of methane and/or ethane, but the relative
proportions are mostly unclear. Understanding the past and current stability of these lakes requires characterizing
the interactions of liquid methane and ethane. Mixtures of these hydrocarbons are not fully understood, and a phase
diagram has not yet been established. Our current cryogenic laboratory setup reaches temperatures down to 30 K,
allowing us to map the full liquidus line (freezing points) of the methane-ethane system as a function of composition
and temperature. While pure methane and ethane both freeze around 91 K, our results show that when mixed, the
freezing point is depressed down to ∼72 K for a mixture of ∼64% methane and ∼36% ethane. Any mixing of these
two species together will depress the freezing point of the lake below Titan’s surface temperature, preventing them
from freezing. Also, when ethane ice forms, it freezes on the bottom of the liquid, while methane ice freezes at the
top of the liquid, implying ethane ice is denser than the solution, while methane ice is less dense; this holds for all
concentrations. Concurrently with the phase diagram determination, we have acquired transmission spectra of these
mixtures to understand how the spectral features change with concentration and temperature. These results will help
interpret future observational data, and guide current theoretical models.
Poster 16
Eclipse-induced changes of Titan’s meteorology at equinox
Tetsuya Tokano1
1
Titan experiences solar eclipses by Saturn on ∼20 consecutive orbits around equinox for durations of up to ∼6 hours.
The impact of these eclipses on Titan's surface, lower atmosphere and middle atmosphere is investigated by a global
climate model. When an eclipse commences, the surface temperature on the subsaturnian side drops by up to 0.3
K, so that the diurnal maximum surface temperature remains lower than on the antisaturnian side, which is never
eclipsed. By contrast, the tropospheric air temperature does not abruptly decrease during the eclipses because of the
large thermal inertia, but the diurnal mean temperature slightly decreases. The surface wind at low latitudes becomes
less gusty in the presence of eclipse due to damping of turbulence. The troposphere outside the planetary boundary
layer is not sensitive to eclipses. In most parts of the stratosphere and mesosphere the temperature decreases by up
to 2 K due to eclipses, but there are also layers, which experience relative warming due to thermal contraction of the
underlying layers. The temperature in the middle atmosphere rapidly recovers after the end of the eclipse season.
Eclipse-induced cooling and warming changes the zonal wind speed by a few m/s due to thermal wind adjustment to
changing latitudinal temperature gradients.
TAC 2016
30 / 35
Posters
Monday
Poster 17
Methane storms as a driver of Titan’s dune orientation.
Benjamin Charnay1 , Erika Barth2 , Scot Rafkin2 , Clément Narteau3 , Sébastien Lebonnois4 , Sébastien Rodriguez5 , Sylvain Courrech du Pont5 and Antoine Lucas5
1
2
SWRI
3
IPGP
LMD
5
Université Paris 7
4
Titan’s equatorial regions are covered by eastward oriented linear dunes [1,2]. This direction is opposite to mean
surface winds simulated by Global Climate Models (GCMs) at these latitudes, oriented westward as trade winds
on Earth. We propose that Titan's dune orientation is actually determined by equinoctial tropical methane storms
producing a coupling with superrotation and dune formation [3]. Using meso-scale simulations of convective methane
clouds [4] with a GCM wind profile featuring the superrotation [5,6], we show that Titan's storms should produce fast
eastward gust fronts above the surface. Such gusts dominate the aeolian transport. Using GCM wind calculations
and analogies with terrestrial dune fields [7], we show that Titan's dune propagation occurs eastward under these
conditions. Finally, this scenario combining global circulation winds and methane storms can explain other major
features of Titan's dunes as the divergence from the equator or the dune size and spacing. It also implies an equatorial
origin of Titan's dune sand and a possible occurence of dust storms.
References:
[1] Lorenz et al. (2006), Science, 312, 724-727.
[2] Lorenz & Radebaugh (2009), Geophysical Research Letter, 36, 3202.
[3] Charnay et al. (2015), Nature Geoscience
[4] Barth & Rafkin. (2007), Geophysical Research Letter, 34, 3203.
[5] Charnay & Lebonnois (2012), Nature Geoscience, 5, 106–109.
[6] Lebonnois et al. (2012), Icarus, 205, 719–721.
[7] Courrech du Pont, Narteau & Gao (2014), Geology, 42, 743–746.
TAC 2016
31 / 35
Social Event
Tuesday
Social Event
A social event is organized on Tuesday 28 at 18:00 in:
Lanson Champagne cellar
66 rue de Courlancy, 51100 Reims
Program:
• Visit of the cellar.
• Champagne tasting of 1, 2 or 3 wine(s):
1. Lanson Black Label Brut (20e)
2. Lanson Black Label Brut + Lanson Rosé Label Brut (25e)
3. Lanson Black Label Brut + Lanson Rosé Label Brut + Lanson Millésimé Brut (30e)
Note:
If you plan to take the tramway, we advise you to purchase your tickets in advance to avoid the queue at
the vending machine during the rush hour.
TAC 2016
32 / 35
Outreach
Wednesday
Outreach / Public conference
A public conference in French is given by Christophe Sotin on Wednesday 29 at 19:00 in:
Auditorium de la Villa Douce,
Université de Reims Champagne-Ardenne
9 boulevard de la Paix, 51100 Reims
Exploration des océans extra-terrestres
L’exploration des environnements de Jupiter et de Saturne par les sondes spatiales Galileo et Cassini nous
a fait découvrir des lunes glacées qui abritent des océans sous leur croûte de glace. Certains de ces océans
sont en contact avec le noyau rocheux. Les conditions sont alors très similaires à celles existant au fond des
océans terrestres où la vie se développe au niveau de sources hydrothermales. La conférence fera le point sur les
ressemblances et différences entre les fonds océaniques terrestres et extraterrestres et décrira les futures missions
spatiales qui exploreront ces mondes océaniques. L’étude de ces environnements, qui ne sont finalement pas si
hostiles qu’on pourrait le penser, peuvent apporter des informations importantes sur l’origine de la vie.
Note:
Free admission subject to availability.
TAC 2016
33 / 35
Participants
List of participants
Abdulsamee
Bruno
Erika
Ludovic
Gordon, L.
Nathalie
Benjamin
Andrew
Daniel
Martin
Thibaud
Athena
Frank
Ravindra, T.
David
Federico
Artem
Michael, F.
Thomas
Jennifer
Sarah
Donald, E.
Antoine
Tommi
Panayotis
Sébastien
Emmanuel
Juan, M.
Ralph, D.
Yingjuan
Luca
Christophe
Edward
Scot
Pascal
Michael
Sébastien
Emilie
Benoît
Joseph
Darci
Christophe
Darrell, F.
Melody
Nicholas
Alexander, E.
Sarah
Gabriel
Tetsuya
Jan
Sandrine
Veronique
Robert
Roger, V.
Eliot, F.
TAC 2016
Alkadrou
Bézard
Barth
Biennier
Bjoraker
Carrasco
Charnay
Coates
Cordier
Cordiner
Cours
Coustenis
Crary
Desai
Dubois
Fabiano
Feofilov
Flasar
Gautier
Hanley
Horst
Jennings
Jolly
Koskinen
Lavvas
Lebonnois
Lellouch
Lora
Lorenz
Ma
Maltagliati
Mathé
Molter
Rafkin
Rannou
Rey
Rodriguez
Royer
Seignovert
Serigano
Snowden
Sotin
Strobel
Sylvestre
Teanby
Thelen
Tigrine
Tobie
Tokano
Vatant d’ollone
Vinatier
Vuitton
West
Yelle
Young
GSMA - Université de Reims Champagne-Ardenne
Observatoire de Paris
NASA/GSFC
Université de Versailles Saint Quentin
UCL-MSSL
GSMA - CNRS - Université de Reims-Champagne-Ardenne
Lab. GSMA, Université de Reims-Champagne-Ardenne
Paris Observatory
University of Colorado, LASP
UCL-MSSL
LATMOS
LMD / IPSL / FX-Conseil, CNRS, Ecole Polytechnique, Univ. Paris-Saclay
NASA - Goddard Space Flight Center
Lowell Observatory
Goddard Space Flight Center
LISA-UPEC
University of Arizona
GSMA
LMD/IPSL, CNRS, UPMC
Observatoire de Paris
UCLA
JHU Applied Physics Lab
UCLA
LESIA - Observatoire de Paris
LATMOS
Southwest Research Institute Boulder
University of Reims
GSMA
AIM - Université Paris Diderot
University of Colorado-Boulder
GSMA - Université de Reims
Jet Propulsion Laboratory - California Institute of Technology
University of Bristol - School of Earth Sciences
New Mexico State University
LATMOS/Synchrotron SOLEIL
LPG / CNRS / U. Nantes
LMD/IPSL
LESIA, Observatoire de Paris-Meudon
IPAG - Univ. Grenoble Alpes / CNRS
Jet Propulsion Lab, Caltech and Univ. Reims Champagne-Ardenne (visiting)
Dept of Planetary Sciences, University of Arizona
34 / 35
Authors Index
Authors index
Achterberg, 16, 17, 19
Adamkovics, 20
Adriani, 11
Alkadrou, 23
Apperé, 28
Bézard, 11, 17, 23, 28
Baines, 13
Bampasidis, 16
Barnes, 20, 29
Barth, 20, 31
Benidar, 24
Berga, 29
Biennier, 24, 25
Bjoraker, 16, 19
Boudon, 23
Bourgalais, 24
Bourgeois, 23
Brinckerhoff, 9
Brown, 13
Buratti, 13
Carles, 24
Carrasco, 8, 10, 25, 27
Cernogora, 27
Chanover, 27
Charnay, 22, 31
Charnley, 14, 26, 27
Clark, 13
Coates, 6, 7
Cordier, 25
Cordiner, 14, 26, 27
Cornet, 11, 28
Cottini, 19
Courrech du Pont, 31
Cours, 25
Coustenis, 16, 19, 23, 28, 29
Crary, 7
D’Aversa, 11
Desai, 6, 7
Dinelli, 11
Dubois, 7, 25
Esposito, 6
Fabiano, 11
Feofilov, 5
Flandinet, 8
Flasar, 16, 17
Fleury, 10
Forget, 22
Garcia-Macias, 8
Gautier, 9, 25
Gavilan, 25
Getty, 9
Grundy, 30
Guillemin, 24
Gurwell, 26
TAC 2016
Hörst, 8, 15
Hanley, 30
Hayes, 29
Hayne, 29
Hidayat, 26
Irwin, 14, 18, 26
Jamal-Eddine, 24
Jennings, 16, 19
Jimson, 6, 27
Joalland, 24
Jolly, 15
Jones, 7
Kataria, 7
Klippenstein, 8, 15
Koskinen, 10
Kuga, 10
Kutepov, 5
Lòpez Puertas, 11
Lara, 26
Lavvas, 8, 10, 11, 15, 16
Lawrence, 13
Le Mouélic, 12, 28
Le Picard, 24
Lebonnois, 17, 31
Lebreton, 29
Lellouch, 26
Lewis, 7
Lindberg, 14, 26
Li, 9, 25
Lora, 20
Lorenz, 21, 29
Lucas, 31
Maltagliati, 11, 25, 28
Marrocchi, 10
Martelli, 29
Marty, 10
Mathé, 25
Ma, 24
Mitchell, 20
Mitri, 29
Molter, 14, 27
Moreno, 26
Moriconi, 11
Moullet, 26
Nagy, 24
Nahon, 8
Narteau, 31
Nicholson, 13
Nikitin, 5, 23
Nixon, 14, 16, 18, 26, 27
Orthous-Daunay, 8
Ovanessian, 11
Petropoulos, 29
Pinnick, 9
Postberg, 29
Rafkin, 21, 31
Rannou, 10–12, 23, 28
Reh, 29
Rey, 5, 23, 25
Rezac, 5
Ridolfi, 11
Rodriguez, 11, 28, 31
Roe, 30
Rotger, 23
Royer, 6, 10
Schinder, 16
Sebree, 9
Seignovert, 10, 12, 25
Serigano, 14, 26, 27
Smith, 6, 27
Snowden, 6, 27
Soderblom, 20, 29
Solomonidou, 28
Sotin, 11–13, 22, 28, 29, 33
Soto, 21
Srama, 29
Strobel, 5
Sylvestre, 18
Teanby, 14, 16–18, 26, 27
Thelen, 27
Thissen, 8
Thompson, 30
Tigrine, 8, 27
Tobie, 22, 29
Tokano, 22, 30
Tortora, 29
Trainer, 9, 25
Trolez, 24
Tyuterev, 5, 23
Vander Auwera, 23
Vettier, 27
Vinatier, 5, 17, 18, 26
Vuitton, 8, 15
Wahlund, 6
Waite, 6, 7
Wellbrock, 6, 7
West, 10, 11, 13
Wordsworth, 22
Wurz, 29
Xu, 13
Yelle, 8, 15
Yen, 29
Young, 20
Zhu, 5
d’Ottavio, 29
de Kok, 18
35 / 35
Monday 27
09:00
09:15
09:35
09:55
10:15
10:35
11:15
11:35
11:55
12:15
14:00
14:20
15:00
15:20
16:00
16:20
16:40
17:00
Welcome
Strobel et al.
Feofilov et al.
Coates et al.
Snowden et al.
Coffee break
Royer et al.
Crary
Dubois
Lunch
Desai et al.
Discussion
Vuitton et al.
Coffee break
Tigrine et al.
Gautier et al.
Carrasco et al.
Poster session
Tuesday 28
09:00
09:20
09:40
10:00
10:20
11:00
11:20
11:40
12:00
13:45
14:25
14:45
15:05
15:45
16:05
16:25
16:45
18:00
Lavvas et al.
Seignovert et al.
West et al.
Fabiano et al.
Coffee break
Maltagliati et al.
Rannou et al.
Sotin et al.
Lunch
Discussion
Cordiner
Molter et al.
Coffee break
Jolly
Yelle et al.
Flasar et al.
Coustenis et al.
Social Event
Wednesday 29
09:00
09:20
09:40
10:00
10:20
11:00
11:20
12:00
13:45
14:05
14:25
14:45
15:05
15:45
16:05
16:25
16:45
19:00
Vinatier et al.
Sylvestre et al.
Teanby et al.
Bjoraker et al.
Coffee break
Jennings
Discussion
Lunch
Young et al.
Lora et al.
Barth
Rafkin et al.
Coffee break
Lorenz
Tokano
Charnay et al.
Discussion
Outreach

TAC 2016 - Abstract book - Université de Reims Champagne

Transcription

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