Article

# Brown, R. H. et al. The identification of liquid ethane in Titan's Ontario Lacus. Nature 454, 607-610

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Department of Planetary Sciences, University of Arizona, Tucson, Arizona 85721, USA.
(Impact Factor: 41.46). 08/2008; 454(7204):607-10. DOI: 10.1038/nature07100
Source: PubMed

ABSTRACT

Titan was once thought to have global oceans of light hydrocarbons on its surface, but after 40 close flybys of Titan by the Cassini spacecraft, it has become clear that no such oceans exist. There are, however, features similar to terrestrial lakes and seas, and widespread evidence for fluvial erosion, presumably driven by precipitation of liquid methane from Titan's dense, nitrogen-dominated atmosphere. Here we report infrared spectroscopic data, obtained by the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini spacecraft, that strongly indicate that ethane, probably in liquid solution with methane, nitrogen and other low-molecular-mass hydrocarbons, is contained within Titan's Ontario Lacus.

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Available from: Jason W. Barnes
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• "C 2 H 6 is found in all four giant planets [4] [5] [6], Titan [7], comets [8] and even as an ice in Kuiper Belt objects [9]. For Titan, observations indicate C 2 H 6 is a constituent of light hydrocarbon lakes [10]. In the atmospheres of the giant planets and Titan, C 2 H 6 is primarily formed from the photolysis of methane, CH 4 [11] [12], and subsequent recombination of methyl radicals, CH 3 [13] [14] [15]. "
##### Article: High-resolution absorption cross sections of C$_{2}$H$_{6}$ at elevated temperatures
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ABSTRACT: Infrared absorption cross sections near 3.3 $\mu$m have been obtained for ethane, C$_{2}$H$_{6}$. These were acquired at elevated temperatures (up to 773 K) using a Fourier transform infrared spectrometer and tube furnace with a resolution of 0.005 cm$^{-1}$. The integrated absorption was calibrated using composite infrared spectra taken from the Pacific Northwest National Laboratory (PNNL). These new measurements are the first high-resolution infrared C$_{2}$H$_{6}$ cross sections at elevated temperatures.
Preview · Article · Oct 2015
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• "While the lakes are thought to be dominated by ethane and methane, there is little direct evidence on the exact amount of these components in the liquid phase. Brown et al. (2008) reported on spectral features observed by the Visible and Infrared Mapping Spectrometer (VIMS) in Ontario Lacus that were interpreted as liquid ethane. Alternatively, Moriconi et al. (2010) suggest the same absorption feature might be in the region surrounding the lake, and could be associated with damp sediments of ethane, propane, methane and possibly other minor hydrocarbons, indicative of retreat due to evaporation. "
##### Article: Experimental constraints on the composition and dynamics of Titan's polar lakes
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ABSTRACT: Titan's polar lakes are thought to be predominantly composed of liquid ethane and methane; however, little is known on the ratio of these hydrocarbons in the lakes, and the stability and dynamics of these mixtures. Here we provide the first experimental constraints under Titan surface conditions of liquid hydrocarbon mixture evaporation. Our results are relevant to Titan's polar temperatures and pressures (∼92 K and 1.5 bar), and cover a wide range of methane–ethane compositions. We show that evaporation is negligible for pure ethane, but increases nearly linearly with increasing methane concentration. Early dissolution of N2 results in ternary mixtures evaporating, which is modeled by a ‘hybrid’ thermodynamic equilibrium approach combining Perturbed-Chain Statistical Associating Fluid Theory with a diffusion and buoyancy-driven mass flux model. The approach follows the experimental evaporation rate measurements presented in this study, and allows for the calculation of the corresponding liquid methane–ethane–nitrogen ratios. Such results along with Cassini inferred lake evaporation rates can be used to estimate the composition of Titan's polar liquids, and may have implications on their origin. Our results suggest that Ontario Lacus is predominantly composed of ethane (>50–80 mol%), indicating it may be a residual lake following extensive seasonal methane evaporation, and/or might be in contact with a subsurface liquid reservoir.
Full-text · Article · Jan 2015 · Earth and Planetary Science Letters
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• "A specular reflection observed in VIMS data also indicates surface liquids (Stephan et al., 2010; Soderblom et al., 2012). Although ethane has been detected as a component of the liquid (Brown et al., 2008), the composition remains largely uncertain (Cordier et al., 2012). The most recent radar analyses indicate that the lakes have a very smooth surface (Zebker et al., 2014) and are remarkably transparent (Mastrogiuseppe et al., 2014), suggesting that they are mostly composed of methane. "
##### Article: Science goals and mission concept for the future exploration of Titan and Enceladus
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ABSTRACT: Saturn's moons, Titan and Enceladus, are two of the Solar System's most enigmatic bodies and are prime targets for future space exploration. Titan provides an analogue for many processes relevant to the Earth, more generally to outer Solar System bodies, and a growing host of newly discovered icy exoplanets. Processes represented include atmospheric dynamics, complex organic chemistry, meteorological cycles (with methane as a working fluid), astrobiology, surface liquids and lakes, geology, fluvial and aeolian erosion, and interactions with an external plasma environment. In addition, exploring Enceladus over multiple targeted flybys will give us a unique opportunity to further study the most active icy moon in our Solar System as revealed by Cassini and to analyse in situ its active plume with highly capable instrumentation addressing its complex chemistry and dynamics. Enceladus' plume likely represents the most accessible samples from an extra-terrestrial liquid water environment in the Solar system, which has far reaching implications for many areas of planetary and biological science. Titan with its massive atmosphere and Enceladus with its active plume are prime planetary objects in the Outer Solar System to perform in situ investigations. In the present paper, we describe the science goals and key measurements to be performed by a future exploration mission involving a Saturn-Titan orbiter and a Titan balloon, which was proposed to ESA in response to the call for definition of the science themes of the next Large-class mission in 2013. The mission scenario is built around three complementary science goals: (A) Titan as an Earth-like system; (B) Enceladus as an active cryovolcanic moon; and
Full-text · Article · Dec 2014 · Planetary and Space Science