Morgan L. Cable

Titan tholins: simulating Titan organic chemistry in the Cassini-Huygens era.

Titan Tholins: Simulating Titan Organic Chemistry in the Cassini-Huygens Era Morgan L. Cable, Sarah M. H€orst, Robert Hodyss, Patricia M. Beauchamp, Mark A. Smith, and Peter A. Willis* NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, United States Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, United States Department of Chemistry, University of Arizona, Tucson, Arizona 85721, United States College of Natural Sciences and Mathematics, University of Houston, Houston, Texas 77004, United States

Luminescent lanthanide sensors

Abstract Luminescent lanthanide optical sensors have been developed that utilize ancillary ligands to enhance detection of a target analyte. In these systems, the lanthanide (ligand) binary complex serves as the receptor, which upon analyte binding forms a ternary complex resulting in detectable change in lanthanide luminescence ( Fig. 1 ). The ancillary ligand improves many properties of analyte detection by protecting the lanthanide and strengthening analyte binding affinity. Encapsulation shields the lanthanide ion from solvent-quenching effects and interfering ions, improving assay sensitivity and selectivity. The ligand-induced enhancement in binding affinity appears to be the result of an increase in positive charge at the analyte binding site due to the electronegative ancillary ligand bound on the opposite hemisphere of the lanthanide. We have elucidated the effects of ancillary ligands for various lanthanide/analyte systems and shown how such effects can greatly improve sensor performance for medical, planetary science, and biodefense applications.

Enceladus Life Finder: The search for life in a habitable Moon

Enceladus is one of the most intriguing bodies in the solar system. In addition to having one of the brightest and youngest surfaces, this small Saturnian moon was recently discovered to have a plume erupting from its south polar terrain and a global subsurface ocean. The Cassini Mission discovered organics and nitrogen-bearing molecules in the plume, as well as salts and silicates that strongly suggest ocean water in contact with a rocky core. However, Cassinis instruments lack sufficient resolution and mass range to determine if these organics are of biotic origin. The Enceladus Life Finder (ELF) is a Discovery-class mission that would use two state-of-the-art mass spectrometers to target the gas and grains of the plume and search for evidence of life in this alien ocean.

Formation of a New Benzene–Ethane Co-Crystalline Structure Under Cryogenic Conditions

We report the first experimental finding of a solid molecular complex between benzene and ethane, two small apolar hydrocarbons, at atmospheric pressure and cryogenic temperatures. Considerable amounts of ethane are found to be incorporated inside the benzene lattice upon the addition of liquid ethane onto solid benzene at 90-150 K, resulting in formation of a distinctive co-crystalline structure that can be detected via micro-Raman spectroscopy. Two new features characteristic of these co-crystals are observed in the Raman spectra at 2873 and 1455 cm(-1), which are red-shifted by 12 cm(-1) from the υ1 (a1g) and υ11 (eg) stretching modes of liquid ethane, respectively. Analysis of benzene and ethane vibrational bands combined with quantum mechanical modeling of isolated molecular dimers reveal an interaction between the aromatic ring of benzene and the hydrogen atoms of ethane in a C-H···π fashion. The most favored configuration for the benzene-ethane dimer is the monodentate-contact structure, with a calculated interaction energy of 9.33 kJ/mol and an equilibrium bonding distance of 2.66 Å. These parameters are comparable to those for a T-shaped co-crystalline complex between benzene and acetylene that has been previously reported in the literature. These results are relevant for understanding the hydrocarbon cycle of Titan, where benzene and similar organics may act as potential hydrocarbon reservoirs due to this incorporation mechanism.

Experimental determination of the kinetics of formation of the benzene-ethane co-crystal and implications for Titan

Benzene is found on Titan and is a likely constituent of the putative evaporite deposits formed around the hydrocarbon lakes. We have recently demonstrated the formation of a benzene-ethane co-crystal under Titan-like surface conditions. Here we investigate the kinetics of formation of this new structure as a function of temperature. We show that the formation process would reach completion under Titan surface conditions in ~18 h and that benzene precipitates from liquid ethane as the co-crystal. This suggests that benzene-rich evaporite basins around ethane/methane lakes and seas may not contain pure crystalline benzene, but instead benzene-ethane co-crystals. This co-crystalline form of benzene with ethane represents a new class of materials for Titans surface, analogous to hydrated minerals on Earth. This new structure may also influence evaporite characteristics such as particle size, dissolution rate, and infrared spectral properties.

Microchip nonaqueous capillary electrophoresis of saturated fatty acids using a new fluorescent dye

We demonstrate nonaqueous labeling and separation of the full range of short to long saturated fatty acids (C2 to C30) for the first time on a microfluidic device. A new fluorescent dye, Pacific Blue hydrazide, labels the carboxylic acid in a two-step, one-pot reaction to enable detection via laser-induced fluorescence at 405 nm excitation. Limits of detection for C10 to C30 acids range from 0.9 to 5.7 μM. Fatty acids were successfully quantified in a sediment sample from the ‘Snake Pit’ hydrothermal system of the Mid-Atlantic Ridge, demonstrating the potential of this method to help characterize microbial communities through targeted biomarker analysis. Such a technique could also be utilized to differentiate between abiotic and biotic compounds in the search for life beyond Earth.

Prospects for mineralogy on Titan

Abstract Saturn’s moon Titan has a surface that is dominated by molecular materials, much of which are photochemically produced in the moon’s atmosphere. This outlook reviews the potential minerals that would be expected to form on the surface and subsurface of Titan from these molecular solids. We seek to classify them and look toward how the future study of these minerals will enhance our understanding of this planetary body. The classification uses the basis of intermolecular interactions, with the materials grouped into “Molecular solids,” “Molecular co-crystals,” and “Hydrates” classes alongside speculation on other possible classes of potential Titan minerals.

The NASA Roadmap to Ocean Worlds

Abstract In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to “identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find.” The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists.

Prospects for organic minerals on Saturn's moon Titan

Titan, the largest moon of Saturn, contains a vast inventory of organic molecules and is considered a prebiotic chemical laboratory on a planetary scale. Active photochemistry in the atmosphere via solar radiation and energy from Saturn’s magnetosphere causes nitrogen and methane to dissociate and recombine, generating organics ranging from simple (ethane, acetylene, HCN) to complex (>10,000 Da) molecules. These molecules continue to react as they move through Titan’s atmosphere, forming aerosol haze layers and eventually depositing on the surface [1].

Understanding Icy Worlds to Maximize Science Return on Future Missions

Missions to the outer planets are challenging. Far beyond the asteroid belt, the Sun is a weak source of energy—radioisotope thermoelectric generators (RTGs) tend to be the power system of choice over solar panels. The radiation environments can be extreme. Yet these icy worlds call to us. Some have icy plumes erupting into space; some are laden with organic material. All of the ingredients for life are there—water, chemistry, and energy—meaning that these planets could be livable environments.