Laboratory measurements of the optical constants of complex organic matter

Grant #: NNX14AF61G
Senior Scientist: Hiroshi Imanaka

Summary of Research Program

Understanding the chemical nature of haze particles in the atmospheres of Titan and Saturn and materials on the surface of the Saturn system bodies is one of the goals of the Cassini-Huygens mission. Complex organic materials may exist as haze layers in the atmospheres of Titan and Saturn and as dark coloring agents on icy satellite surfaces. Laboratory measurements of optical constants of laboratory haze/condensate analogs at broad spectral wavelengths are crucial for the effort of interpreting the spectral observations by the Cassini-Huygens mission. However, there is a general lack of studies in vacuum ultraviolet, near-IR, and far-IR spectral regions, which is necessary for the Cassini’s UVIS, VIMS, and CIRS instruments. We propose to determine the optical constants of laboratory-generated complex organic matter in the wavelength region between 0.030 μm and 500 μm (20 cm-1), which covers spectral region crucial for the Cassini spectroscopic instruments (the UVIS, ISS, VIMS, and CIRS) and the DISR on the Huygens Probe. Our initial effort would be focused on the plausible organic hazes in Titan and Saturn by investigating complex organic materials 1) with/without nitrogen inclusion and 2) various degree of saturation [(H-N)/C]. Comlex organics consisting of C/H/O elements will also be investigated as potential organic matter on the surface of icy bodies and Saturn’s ring particles. Reliable optical constants from this proposed work would help the effort in interpretation of broad spectral observations by the Cassini mission to constrain the chemical and physical nature of those organic haze materials.

Research Goals

We propose to determine the optical constants of laboratory generated complex organic matter in the wavelength region between 0.030 μm and 500 μm (20 cm-1), which is crucial for interpreting observations by the Cassini spectroscopic instruments (the UVIS, ISS, VIMS, and CIRS) and the DISR on the Huygens Probe. The objectives of this proposal are as follows;

Goal 1: Determine the optical constants (n + ik) of Titan haze analogs at wavelengths between 30 nm and 500 μm (20 cm-1), to help constrain the chemical nature of Titan’s haze particles.

Goal 2: Reveal the difference/similarity of optical constants of Titan and Saturn’s haze analogs, by investigating the complex organic matter consisting of only C/H elements. This may provide a guide for the likely optical constants of Saturn haze particles, and this comparison may reveal the uniqueness of Titan haze particles with possible nitrogen inclusion.

Goal 3: Correlate, empirically but quantitatively, the optical constants in the UV/Vis/Near-IR region with specific absorption band shapes observed in the IR spectral region, such as band shape at 3.4 μm region. Systematic measurements of optical constants in broad spectral region might help us correlate the specific fingerprints with the coloration in the visible spectral region.

Goal 4: Determine the optical constants of complex organic matter consisting of C/H/O elements, which could serve as an end member of the potentially plausible organic matter on the surface of icy bodies.