[Show abstract][Hide abstract] ABSTRACT: Titan, the moon of Saturn with a thick atmosphere and an active hydrocarbon-based weather cycle, is considered the best target in the solar system for the study of organic chemistry on a planetary scale. Microfluidic devices that employ liquid phase techniques such as capillary electrophoresis with ultrasensitive laser-induced fluorescence detection offer a unique solution for in situ analysis of complex organics on Titan. We previously reported a protocol for nonaqueous microfluidic analysis of primary aliphatic amines in ethanol, and demonstrated separations of short- and long-chain amines down to -20 °C. We have optimized this protocol further, and used it to analyze Titan aerosol analogues (tholins) generated in two separate laboratories under a variety of different conditions. Ethylamine was a major product in all samples, though significant differences in amine content were observed, in particular for long-chain amines (C12-C27). This work validates microfluidic chemical analysis of complex organics with relevance to Titan, and represents a significant first step in understanding tholin composition via targeted functional group analysis.
[Show abstract][Hide abstract] ABSTRACT: Abstract The discovery of large (>100 u) molecules in Titan's upper atmosphere has heightened astrobiological interest in this unique satellite. In particular, complex organic aerosols produced in atmospheres containing C, N, O, and H, like that of Titan, could be a source of prebiotic molecules. In this work, aerosols produced in a Titan atmosphere simulation experiment with enhanced CO (N(2)/CH(4)/CO gas mixtures of 96.2%/2.0%/1.8% and 93.2%/5.0%/1.8%) were found to contain 18 molecules with molecular formulae that correspond to biological amino acids and nucleotide bases. Very high-resolution mass spectrometry of isotopically labeled samples confirmed that C(4)H(5)N(3)O, C(4)H(4)N(2)O(2), C(5)H(6)N(2)O(2), C(5)H(5)N(5), and C(6)H(9)N(3)O(2) are produced by chemistry in the simulation chamber. Gas chromatography-mass spectrometry (GC-MS) analyses of the non-isotopic samples confirmed the presence of cytosine (C(4)H(5)N(3)O), uracil (C(5)H(4)N(2)O(2)), thymine (C(5)H(6)N(2)O(2)), guanine (C(5)H(5)N(5)O), glycine (C(2)H(5)NO(2)), and alanine (C(3)H(7)NO(2)). Adenine (C(5)H(5)N(5)) was detected by GC-MS in isotopically labeled samples. The remaining prebiotic molecules were detected in unlabeled samples only and may have been affected by contamination in the chamber. These results demonstrate that prebiotic molecules can be formed by the high-energy chemistry similar to that which occurs in planetary upper atmospheres and therefore identifies a new source of prebiotic material, potentially increasing the range of planets where life could begin. Key Words: Astrochemistry-Planetary atmospheres-Titan-Astrobiology. Astrobiology 12, 809-817.
[Show abstract][Hide abstract] ABSTRACT: Groups of peaks with mass spacing of ∼13.5 are observed in all of the
tholin spectra. Analysis of the Orbitrap tholin measurements indicates
that these groups EPSC Abstracts Vol. 6, EPSC-DPS2011-1627, 2011
EPSC-DPS Joint Meeting 2011 c Author(s) 2011 can be defined by
molecules that have a constant number of heavy atoms (C+N). The average
number of C, N, and H atoms in each group increases linearly as a
function of increasing mass. These trends can therefore be extrapolated
to the higher masses observed in the CAPS measurements as a first
estimate of the possible composition of those molecules. The spacing
appears to be a consequence of the degree of saturation of the
molecules. The INMS spectra and the CAPSIBS (positive ions) spectra
exhibit groups of very regularly spaced peaks as well. The spacing in
the INMS data is ∼12.5 but seems to increase towards 13.5 for the
heavier masses in the CAPS-IBS data. The spacing change may be
indicative of the transition from gas phase molecules to aerosols.
[Show abstract][Hide abstract] ABSTRACT: Titan, the organic-rich moon of Saturn, possesses a thick atmosphere of nitrogen, globally covered with organic haze layers. The recent Cassini's INMS and CAPS observations clearly demonstrate the importance of complex organic chemistry in the ionosphere. EUV photon radiation is the major driving energy source there. Our previous laboratory study of the EUV-VUV photolysis of N2/CH4 gas mixtures demonstrates a unique role of nitrogen photoionization in the catalytic formation of complex hydrocarbons in Titan's upper atmosphere (Imanaka and Smith, 2007, 2009). Such EUV photochemistry could also have played important roles in the formation of complex organic molecules in the ionosphere of the early Earth. It has been suggested that the early Earth atmosphere may have contained significant amount of reduced species (CH4, H2, and CO) (Kasting, 1990, Pavlov et al., 2001, Tian et al., 2005). Recent experimental study, using photon radiation at wavelengths longer than 110 nm, demonstrates that photochemical organic haze could have been generated from N2/CO2 atmospheres with trace amounts of CH4 or H2 (Trainer et al., 2006, Dewitt et al., 2009). However, possible EUV photochemical processes in the ionosphere are not well understood. We have investigated the effect of CO2 in the possible EUV photochemical processes in simulated reduced early Earth atmospheres. The EUV-VUV photochemistry using wavelength-tunable synchrotron light between 50 - 150 nm was investigated for gas mixtures of 13CO2/CH4 (= 96.7/3.3) and N2/13CO2/CH4 (= 90/6.7/3.3). The onsets of unsaturated hydrocarbon formation were observed at wavelengths shorter than the ionization potentials of CO2 and N2, respectively. This correlation indicates that CO2 can play a similar catalytic role to N2 in the formation of heavy organic species, which implies that EUV photochemistry might have significant impact on the photochemical generation of organic haze layers in the upper atmosphere of the early Earth.
[Show abstract][Hide abstract] ABSTRACT: The large abundance of NH3 in Titan's upper atmosphere is a consequence of coupled ion and neutral chemistry. The density of NH3 is inferred from the measured abundance of NH4+. NH3 is produced primarily through reaction of NH2 with H2CN, a process neglected in previous models. NH2 is produced by several reactions including electron recombination of CH2NH2+. The density of CH2NH2+ is closely linked to the density of CH2NH through proton exchange reactions and recombination. CH2NH is produced by reaction of N(2D) and NH with ambient hydrocarbons. Thus, production of NH3 is the result of a chain of reactions involving non-nitrile functional groups and the large density of NH3 implies large densities for these associated molecules. This suggests that amine and imine functional groups may be incorporated as well in other, more complex organic molecules.
[Show abstract][Hide abstract] ABSTRACT: The observations by the Cassini Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) clearly demonstrate the importance of complex organic chemistry in the upper atmosphere of Titan; a complex coupling of neutral and ion chemistry for organic aerosol generation induced by EUV photons and Saturn's magnetospheric charged particles. To understand the dominant energy source for aerosol formation and its formation chemistry, we comparatively investigate the chemical mechanism in N2/CH4 gas mixtures resulting from EUV-VUV synchrotron radiation (50-150 nm) and tunable mono-energetic electron beam irradiation (5 eV - 2000 eV). These excitation energy sources cover the dominant energy source available in Titan's upper atmosphere. Our previous study of the EUV-VUV photolysis of N2/CH4 gas mixtures revealed the unique role of nitrogen photoionization in the catalytic formation of complex hydrocarbons and in the major nitrogen fixation process in Titan's upper atmosphere (Imanaka and Smith, 2007, 2009, 2010). However, relative roles of ion-molecule reactions and radical/neutral reactions in such complex chemistry remain to be determined. We characterized the electron energy distribution by conducting the Langmuir probe measurements. Degradation of the primary photoelectron from N2 photoionization at 20.6 eV photons is clearly observed, and the electron density rapidly decreases down to 109-10 cm-3, which suggests the complex coupling of ion-molecular reactions and dissociative ion-electron recombination reactions for the observed development of complex organic molecules. The electron beam irradiation experiments at energy larger than 200 eV shows distinct gaseous product distribution with nitrogenated gaseous species from those with EUV irradiation products. The generation of secondary electrons and multiple inelastic collisions of fast electrons might increases the nitrogen fixation efficiency. The much less stringent spin selection rules could provide many additional chemical pathways not open to optical absorption processes. We acknowledge support from the NASA grants NNX08AO13G, NNX09AM95G, NNX10AF08G, and the NAI program.
[Show abstract][Hide abstract] ABSTRACT: We show that certain types of organic molecules that might exist on Mars are resistant to UV photolysis. Data obtained by thermal decomposition of irradiated organic molecules could help constrain the chemical composition of Martian organics.
[Show abstract][Hide abstract] ABSTRACT: The Phoenix lander is the first mission since Viking that could detect organics. Mellitic acid is a possible decay product of meteoritic organics. We irradiate mellitic acid with UV, producing a residue to analyze and compare to Phoenix results.
[Show abstract][Hide abstract] ABSTRACT: Experimental simulations of the initial steps of the ionic chemistry
occurring in the ionosphere of Titan were performed at the synchrotron
source Elettra in Trieste. The measurements consisted in irradiating
with a monochromatic beam of variable wavelength (from the methane
ionization edge at 12.6 eV, up to the molecular nitrogen dissociative
ionization edge, beyond 24.3 eV) 3 gas mixtures of increasing
complexity. The resulting ionic chemistry was recorded by means of a
high-resolution ion trap. Experimental results give conclusive
information on the validity of ion-chemistry reaction rates used to
perform kinetic simulations, but reveal as well new processes, never
described earlier. These will be discussed and compared to model
[Show abstract][Hide abstract] ABSTRACT: Organic macromolecules ("complex tholins") were synthesized from a 0.95 N(2)/0.05 CH(4) atmosphere in a high-voltage AC flow discharge reactor. When placed in liquid water, specific water soluble compounds in the macromolecules demonstrated Arrhenius type first order kinetics between 273 and 313 K and produced oxygenated organic species with activation energies in the range of approximately 60+/-10 kJ mol(-1). These reactions displayed half lives between 0.3 and 17 days at 273 K. Oxygen incorporation into such materials--a necessary step toward the formation of biological molecules--is therefore fast compared to processes that occur on geologic timescales, which include the freezing of impact melt pools and possible cryovolcanic sites on Saturn's organic-rich moon Titan.
[Show abstract][Hide abstract] ABSTRACT: The success of the Huygens mission does not overshadow the importance of
laboratory simulations of gas-phase and surface reactions that might
occur in Titan's atmosphere and surface, respectively. We present here
our latest results on chemical reactions (hydrolysis, peroxidation and
hydrogenation) of laboratory made tholins obtained by FT-ICR mass
spectrometry. The laboratory synthesis of tholins has been described in
our earlier papers [1,2]. Overall, we conclude that our laboratory
tholins are reactive materials that undergo fast hydrolysis, oxidation
and reduction. Thus, if the tholin on Titan's surface resemble our
laboratory made tholins, it can be considered as a potential starting
material for several synthetic processes that can provide organic
compounds of pre-biotic interest.
Hydrolysis reactions occur with rate constants of 2-10 hour-1
at room temperature. Formal water addition to several species of
CxHyNz has been observed by detecting
the formation of CxHy+2NzO species.
MS/MS fragmentation of the oxygen containing ions leads to the loss of
water, ammonia, HCN, acetonitrile, etc. This suggests that tholin
hydrolysis may occur in temporary melted ponds of water/ammonia ice on
Titan. Peroxidation, which can be considered as a very harsh oxidation,
leads to mono-, and multiple oxygenated compounds within a few minutes.
The MS/MS fragmentation of these compounds suggests the presence of
organic amides and, presumably, amino acid like compounds. Hydrogenation
leads to compounds in which the originally present carbon-carbon or
carbon-nitrogen double and triple bonds are saturated. H/D exchange
experiments show different kinetics depending on the degree of
unsaturation/saturation and the number of N atoms.
 Sarker, N.; Somogyi, A.; Lunine, J. I.; Smith, M. A. Astrobiology,
2003, 3, 719-726.
 Somogyi, A.; Oh, C-H.; Lunine, J. I.; Smith, M. A. J. Am. Soc. Mass
Spectrom. 2005, 16, 850-859.