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PAMPRE and the Chemistry of Neutral Species in Titan’s Upper Atmosphere
David Dubois, Nathalie Carrasco, Sarah Tigrine, Ludovic Vettier, Guy Cernogora
To cite this version:
David Dubois, Nathalie Carrasco, Sarah Tigrine, Ludovic Vettier, Guy Cernogora. PAMPRE and the Chemistry of Neutral Species in Titan’s Upper Atmosphere. Exobiologie Jeunes Chercheurs 2015, Nov 2015, Paris, France. 2015. �insu-01336838�
PAMPRE and the Chemistry of Neutral Species in
Titan’s Upper Atmosphere
D. Dubois, N. Carrasco, S. Tigrine, L. Vettier, G. Cernogora
Université Versailles St-Quentin, UPMC Univ. Paris 06, CNRS, LATMOS, 11 Blvd. d’Alembert, 78280 Guyancourt, France
[1] Abstract
[2] Introduction
[4] Infrared Spectroscopy
[5] Mass Spectrometry
References
[6] Perspectives
A complex atmospheric photochemistry has been revealed in Titan’s
atmosphere by the ongoing Cassini-Huygens mission. Its
composition mainly made out of N
2-CH
4leads to ionization and
photo-dissociative processes that eventually form solid organic aerosols
called tholins. Tholins are assumed to be formed in the ionosphere,
where they coexist with the gas phase, in an ionic and neutral medium.
The PAMPRE set-up aims at simulating the reactivity and production of
solid aerosols in Titan’s ionospheric conditions through heterogeneous
chemistry in a radiofrequency-induced plasma.
In this study, our aim was to accumulate gas products in an N
2-CH
4(90-10%) mixture using a cold trap to retain the products. These were
then released after end of cooling and analyzed with infrared
spectroscopy and mass spectrometry in order to better understand the
chemical reactivity at work.
Fig. 9. (a) Ion mass spectra measured in an RF plasma (adapted from
Mutsukura, 2001)
(b) Qualitative comparison of positive ions in an RF plasma and in
Titan’s ionosphere (Carrasco et al., 2012)
Ø Cable, M., Hörst, S., Hodyss, R., Beauchamp, P., Smith, M., Willis, P., 2011. Titan
Tholins: Simulating Titan Organic Chemistry in the Cassini-Huygens Era, Chem. Rev., 112, 1882-1909.
Ø Carrasco, N., Gautier, T., Es-sebbar, E., Pernot, P., Cernogora, G., 2012. Volatile
products controlling Titan’s tholins production. Icarus 219, 230-240.
Ø Mandt, K., et al., 2012. Ion densities and composition of Titan’s upper atmosphere,
JGR, 117, E10006.
Ø Mutsukura, N., 2001. Deposition of diamondlike carbon film and mass spectrometry
measurement in CH4/N2 RF plasma. Plasma Chem. Plasma Process. 21, 265–277.
Ø Szopa, C., Cernogora, G., Boufendi, L., Correia, J-J., Coll, P., 2006. PAMPRE: A dusty
plasma experiment for Titan's tholins production and study. Planetary and Space Science, 54, 394-404.
Fig. 1. The intense photochemistry leading up to
the formation of aerosols that make up the hazy layers on Titan. Image credit: ESA/ATG medialab
Fig. 2. The PAMPRE RF plasma experiment
(Szopa et al., 2006)
[3] The experiment
Fig. 4. The cryogenic trap system
2015
o The cryogenic trap
was set at a
temperature of Tº=
100 K in order to try
and trap as many
products as possible
1000 1500 2000 2500 3000 3500 4000 0 0.02 0.04 0.06 0.08 0.1 0.12 Wav e n u m b e r ( c m - 1) Ab so rb a n ceI n f r ar e d ab sor b an c e of t h e r e l e ase d gas p r o d u c t s af t e r 10m n an d 24h of w ar m i n g
t=10mn of warming t=24h of warming 1500 2000 2500 3000 3500 4000 0 0.02 0.04 0.06 0.08 0.1 0.12 Wav e n u m b e r ( c m - 1) Abs o rb a n c e R e p r o d u c i b i l i ty i n i n f r ar e d ab sor b an c e of t h e gas p r o d u c t s Gas products released after 24h (1st run)
Gas products released after 21h (2nd run)
0 150 300 450 600 750 900 1050 1200 1350 1500 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 T i m e ( m n ) Pr e ss u re (m b a r)
P r e ssu r e e v ol u t i on of t h e r e l e ase d gas p r o d u c t s d u r i n g w ar m i n g f or 21h
0.38 0.70 0.74 0.93 1.28 1.60 1.84 Gas product pressures
o In light of this study of neutral species, the next step
will be to analyze positive and negative ions by
secondary ion mass spectrometry coupled with the
reactor.
Fig. 6. Infrared absorption of the gas products released after
cryogenic trap, with zoom centered at 4000 cm-1, compared
with the GEISA spectroscopy database
Fig. 7. Test of reproducibility
o Data provided by
the INMS
instrument
onboard Cassini
showed the
prevalence of ion
chemistry leading
to the formation
of the tholins
(Mandt et al.,
2012).
Fig. 5. Pressure evolution of the gas
products released after end of cooling
Fig. 3. Background mass spectrum
0 10 20 30 40 50 60 70 80 90 100 1 2 3 4 5 6 7x 10 −10 M ass ( am u ) Io n c u rr e n t [A ] B ac k gr ou n d N 2- C H 4 m ass sp e c t r u m Background 0 10 20 30 40 50 60 70 80 90 100 10−14 10−13 10−12 10−11 10−10 10−9 10−8 M ass ( am u ) Io n c u rr e n t [A ] M ass sp e c t r a of gas p r o d u c t s i n an N 2- C H 4 m i x t u r e
Products released after 7mn (P=0.38 mbar) Products released after 32mn (P=0.70 mbar)
0 10 20 30 40 50 60 70 80 90 100 10−14 10−13 10−12 10−11 10−10 10−9 10−8 M a s s ( a m u ) Io n c u rr e n t [A ] M a s s s p e c t r a o f g a s p r o d u c t s i n a n N 2 - C H 4 m i x t u r e
Products released after 76mn (P=0.74 mbar) Products released after 125mn (P=0.93 mbar)
0 10 20 30 40 50 60 70 80 90 100 10−14 10−13 10−12 10−11 10−10 10−9 10−8 M as s ( am u ) Io n c u rr e n t [A ] M as s s p e c t r a of gas p r o d u c t s i n an N 2- C H 4 m i x t u r e
Products released after 190mn (P=1.28 mbar) Products released after 300mn (P=1.60 mbar)
0 10 20 30 40 50 60 70 80 90 100 10−14 10−13 10−12 10−11 10−10 10−9 10−8 M as s ( am u ) Io n c u rr e n t [A ] M as s s p e c t r u m of al l gas p r o d u c t s i n an N 2- C H 4 m i x t u r e
Products released after 21h (P=1.84 mbar)
Fig. 8. Gas products released after 32mn (a), 125mn (b), 300mn (c) and 21h
(d). The final pressure of gas products attained here is 1.84 mbar. For the first 32mn, C1 and C2 molecules are already well present. C3 and C4
compounds appear after 76mn. C5, C6 and higher mass molecules are detectable back at room temperature, at the end of our experiment.
