2014 Annual Science Report

NASA Jet Propulsion Laboratory - Titan Reporting  |  SEP 2013 – DEC 2014

Longer Wavelength Photochemistry of Condensates and Aerosols in Titan’s Lower Atmosphere and on the Surface

Project Summary

This study focuses on the condensed phase photochemistry on Titan. In particular, we focus on understanding longer wavelength photochemistry of solid hydrocarbons so simulate photochemistry that could occur based on the UV penetration through the atmosphere and on the evolution of complex organic species in astrobiologically significant regions on Titan’s surface. Here we investigate the oxygenation chemistry involving the condensed Titan’s organic aerosols with water-ice on Titan’s surface – induced by high energy photons simulating the cosmic ray induced chemistry on Titan’s surface.

4 Institutions
3 Teams
2 Publications
0 Field Sites
Field Sites

Project Progress

The majority of our laboratory work was focused during the Summer June – August 2014, during which one joint PhD student (Benjamin Fleury) and one masters student (Laura Selliez) from the collaborator Prof. Nathalie Carrasco’s group worked with Murthy Gudipati in conducting the experimental work. The focus of this work is to determine whether photons at longer wavelength could induce chemical reactions involving one of the most abundant unsaturated molecules in Titan’s atmosphere: acetylene when accreted on to laboratory generated “tholins and organic polymers” – analogs of Titan’s aerosols and surface organics. We were successful and observed consistently that acetylene is depleted during photolysis only when adsorbed on tholins. One publication for a high-impact journal is in preparation, involving Bob West and the Cassini team and two French teams.

During March-April 2014 Murthy Gudipati took various tholin samples, including the photopolymer from dicyano acetylene (C4N2) — which was the focus of our Nature Communications Paper in 2013 — to Grenoble to Veronique Vuitton’s lab to conduct their mass spectroscopic analysis. The results from these “orbitrap” mass spectrometry are very exciting. We could clearly see dimers, trimers of C4N2, further evidence for longer-wavelength induced photopolymerization in condensed Titan’s molecular ices. One publication is in preparation.

Infrared spectra of non-volatile residue obtained at room temperature produced by λ>300 nm photochemistry of C4N2 ice compared with the spectra of tholins made from electrical discharge experiments and Cassini CIRS and VIMS data in the far IR and mid IR, respectively. The olefinic, aromatic, and aliphatic IR bands are shifted to lower frequency (red arrow), whereas the nitrile (-CN) and isonitrile (-NC) bands are shifted to higher frequency (blue arrow) in the UV photolysis experiments relative to discharge studies.

    Murthy Gudipati
    Project Investigator

    Nathalie Carrasco

    Isabelle Couturier

    Benjamin Fleury

    Véronique Vuitton

    Robert West

    Objective 1.1
    Formation and evolution of habitable planets.

    Objective 2.2
    Outer Solar System exploration

    Objective 3.1
    Sources of prebiotic materials and catalysts

    Objective 3.2
    Origins and evolution of functional biomolecules

    Objective 3.3
    Origins of energy transduction