2014 Annual Science Report
NASA Jet Propulsion Laboratory - Titan Reporting | SEP 2013 – DEC 2014
Investigation of Electron-Molecule Chemistry and Micrometeorite Induced Reactions on Titan’s Surface
Low-energy electron-beam irradiation and dissociative electron attachment (DEA) experiments were performed on nitrogen-containing organic condensates as a model for cosmic-ray induced polymerization processes and charging events that can occur within Titan’s atmosphere and on Titan’s organic-rich surface. In addition, detailed analysis of meteorite surfaces were analyzed with an emphasis of understanding the corrosion of schreibersite and the role this may play in the formation of phosphorylated pre-biotic molecules.
Dissociative electron attachment (DEA) experiments were performed on nitrogen-containing organic condensates as a model for low-energy electron-induced polymerization processes and charging events that can occur within Titan’s atmosphere. DEA experiments were performed to probe the desorption of H- from hydrogen cyanide (HCN), acetonitrile (CH3CN), and aminoacetonitrile (NH2CH2CN) ices, as well as from synthesized tholin materials condensed or deposited onto a graphite substrate maintained at low temperature (90-130 K). H- desorption cross-sections were acquired from these organics upon low-energy electrons irradiation (3-15 eV) and compared to that of synthesized tholin material. Chemical and structural transformations of HCN upon electron irradiation were investigated using X-ray photoelectron (XPS) and Fourier-transform infrared (FTIR) spectroscopy techniques. In addition, information regarding the charging properties of these condensates has been obtained to study the relationship between DEA processes and surface charging of organic aerosols likely present in the atmosphere of Titan.
We have also completed a comprehensive investigation of schreibersite inclusions within meteorites, the associated intrinsic low-temperature oxidation products as well as synthetic schreibersite surrogates Fe3P and Fe2NiP using surface characterization techniques. These include micro-Raman spectroscopy, atomic force microscopy (AFM), electrostatic force microscopy (EFM), electron microprobe (EPMA), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). In addition, thermodynamic equilibrium modeling of the oxidation of schreibersite was carried out. We determined that oxidation of schreibersite is mostly limited to the surface in the absence of other ions and/or water. This oxidation occurs rapidly at the surface and is mediated by the atmosphere, forming primarily iron oxides and iron phosphates. In addition, we also demonstrated that synthetic schreibersite surrogates are reasonable chemical proxies for natural schreibersite, bearing similar chemistry both at the surface and at depth. These meteorite inclusions and corrosion products may play a role in stimulating the formation of pre-biotic molecules on Titan’s surface.
PROJECT MEMBERS:Thomas Orlando
RELATED OBJECTIVES:Objective 3.1
Sources of prebiotic materials and catalysts
Origins and evolution of functional biomolecules
Biosignatures to be sought in Solar System materials