Laboratory measurements of cryogenic liquid alkane microwave absorptivity and implications for the composition of Ligeia Mare, Titan

Mitchell, K. L.; Barmatz, M.; Jamieson, Corey S.; Lorenz, Ralph D.; Lunine, Jonathan I.

doi:10.1002/2014gl059475

Cited by 48 publications

(41 citation statements)

References 27 publications

(57 reference statements)

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“…Such a low best fit dielectric constant not only is consistent with liquid hydrocarbons but also suggests that the composition of Ligeia Mare is dominated by liquid methane rather than liquid ethane (see Figure and Table ). Recent laboratory measurements [ Mitchell et al ., ] have confirmed previous work (see a review in Lorenz et al . [, Table 1]) showing that pure liquid methane has a significantly lower dielectric constant (~1.7) than pure liquid ethane (~2).…”

Section: Resultssupporting

confidence: 90%

“…It is very close to the value measured in laboratory by Mitchell et al . [] which found liquid methane to have ~5 times smaller loss tangent than liquid ethane (see Table ). Nitrogen has a loss tangent somewhat close to that of pure methane.…”

Section: Resultsmentioning

confidence: 99%

“…They found a (very low) value of (4.8 ± 1.0) × 10 −5 for the loss tangent, which suggests a methane‐dominated composition, based on comparison with laboratory data acquired by Mitchell et al . []. It is the extreme transparency of the sea liquid to microwaves that allows the radiometer (and the radar) to sample depths as great as several thousand times its operating wavelength.…”

Section: Introductionmentioning

confidence: 99%

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Composition, seasonal change, and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission

Gall

Malaska

Lorenz

et al. 2016

J. Geophys. Res. Planets

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For the last decade, the passive radiometer incorporated in the Cassini RADAR has recorded the 2.2 cm wavelength thermal emission from Titan's seas. In this paper, we analyze the radiometry observations collected from February 2007 to January 2015 over one of these seas, Ligeia Mare, with the goal of providing constraints on its composition, bathymetry, and dynamics. In light of the depth profile obtained by Mastrogiuseppe et al. (2014) and of a two-layer model, we find that the dielectric constant of the sea liquid is <1.8, and its loss tangent is < 3:6 þ4:3 À2:1 Â10 À5 . Both results point to a composition dominated by liquid methane rather than ethane. A high methane concentration suggests that Ligeia Mare is primarily fed by methane-rich precipitation and/or ethane has been removed from it (e.g., by crustal interaction). Our result on the dielectric constant of the seafloor is less constraining < 2:9 þ0:9 À0:9 À Á , but we favor a scenario where the floor of Ligeia Mare is covered by a sludge of compacted and possibly nitrile-rich organic material formed by the deposition of photochemical haze or by rain washing of the nearby shores. We use these results to produce a low-resolution bathymetry map of the sea. We also estimate the temperature variation of the bulk sea between February 2007 and July 2013 to be <2 K, which provides a constraint on its net evaporative cooling currently being explored in ocean circulation models. Lastly, we suggest a lag in the summer warming of the northern polar terrains.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Composition, seasonal change, and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission

Gall

Malaska

Lorenz

et al. 2016

J. Geophys. Res. Planets

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“…Because they are impossible to form naturally in a warmer world containing water and oxygen, only future exploratory missions to Titan can test the hypothesis that natural chemical systems evolve chemical complexity in almost any circumstance (3). The larger seas of Titan have been determined by radar sounding to be mostly methane with significant admixtures (∼10%) of ethane and nitrogen (27,28). Because HCN is mostly insoluble in such mixtures (29), it is unlikely that polymers will form there.…”

Section: Speculations On the Implications Of These Results For Life Wmentioning

confidence: 99%

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

Rahm

Lunine

Usher

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The chemistry of hydrogen cyanide (HCN) is believed to be central to the origin of life question. Contradictions between Cassini-Huygens mission measurements of the atmosphere and the surface of Saturn's moon Titan suggest that HCN-based polymers may have formed on the surface from products of atmospheric chemistry. This makes Titan a valuable "natural laboratory" for exploring potential nonterrestrial forms of prebiotic chemistry. We have used theoretical calculations to investigate the chain conformations of polyimine (pI), a polymer identified as one major component of polymerized HCN in laboratory experiments. Thanks to its flexible backbone, the polymer can exist in several different polymorphs, which are relatively close in energy. The electronic and structural variability among them is extraordinary. The band gap changes over a 3-eV range when moving from a planar sheet-like structure to increasingly coiled conformations. The primary photon absorption is predicted to occur in a window of relative transparency in Titan's atmosphere, indicating that pI could be photochemically active and drive chemistry on the surface. The thermodynamics for adding and removing HCN from pI under Titan conditions suggests that such dynamics is plausible, provided that catalysis or photochemistry is available to sufficiently lower reaction barriers. We speculate that the directionality of pI's intermolecular and intramolecular =N-H … N hydrogen bonds may drive the formation of partially ordered structures, some of which may synergize with photon absorption and act catalytically. Future detailed studies on proposed mechanisms and the solubility and density of the polymers will aid in the design of future missions to Titan.hydrogen cyanide | prebiotic chemistry | Titan | polymers S aturn's moon Titan is a carbon-rich, oxygen-poor world with a wide range of organic compounds, atmospheric energy sources, and alkane liquid seas-all measured by the remarkably successful Cassini-Huygens mission (1). The extreme cold puts liquid water out of reach-buried 50-100 km below a frigid ice crust (2). The lack of liquid water and presence of liquid hydrocarbons makes Titan a unique "natural laboratory" for exploring potential nonterrestrial forms of prebiotic chemistry or, more speculatively, biochemistry, whose essential biopolymers would differ profoundly from terrestrial ones (3). Regardless of the specific chemistry involved, life requires polymorphic molecules that combine flexibility with the ability to form the organized metastable structures needed for function, adaptation, and evolution. This, almost certainly, requires extended molecules capable of intermolecular and intramolecular hydrogen bonding, but such bonds need not involve oxygen; nitrogen is a potential surrogate. Although =N-H . . . N bonds are weaker than those involving oxygen, their energies are large compared with thermal energy (kT ∼ 0.18 kcal/mol at Titan's low temperature, 90-94 K) and intermolecular and intramolecular bonds need not compete with the strong -O-H . ...

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“…While we focused on an ethane-rich EMP mixture, recent comparisons of microwave absorptivity between the high-latitude northern sea "Ligeia Mare" and the southern hemisphere lake "Ontario Lacus" suggest that other lake/sea compositions, including some of primarily methane, 27,28 are also found on Titan. To see if such variations would significantly affect our results, we conducted additional simulations to compute the PMFs of a single ACN molecule in pure methane, pure ethane, and the EMP liquid (Figure 3).…”

Section: Molecular Dynamics Resultsmentioning

confidence: 99%

Acetonitrile cluster solvation in a cryogenic ethane-methane-propane liquid: Implications for Titan lake chemistry

Corrales

Trumbo

et al. 2017

The Journal of Chemical Physics

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The atmosphere of Titan, Saturn's largest moon, exhibits interesting UV-and radiation-driven chemistry between nitrogen and methane, resulting in dipolar, nitrile-containing molecules. The assembly and subsequent solvation of such molecules in the alkane lakes and seas found on the moon's surface are of particular interest for investigating the possibility of prebiotic chemistry in Titan's hydrophobic seas. Here we characterize the solvation of acetonitrile, a product of Titan's atmospheric radiation chemistry tentatively detected on Titan's surface [H. B. Niemann et al., Nature 438, 779-784 (2005)], in an alkane mixture estimated to match a postulated composition of the smaller lakes during cycles of active drying and rewetting. Molecular dynamics simulations are employed to determine the potential of mean force of acetonitrile (CH 3 CN) clusters moving from the alkane vapor into the bulk liquid. We find that the clusters prefer the alkane liquid to the vapor and do not dissociate in the bulk liquid. This opens up the possibility that acetonitrile-based microscopic polar chemistry may be possible in the otherwise nonpolar Titan lakes.

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Laboratory measurements of cryogenic liquid alkane microwave absorptivity and implications for the composition of Ligeia Mare, Titan

Cited by 48 publications

References 27 publications

Composition, seasonal change, and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission

Composition, seasonal change, and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

Acetonitrile cluster solvation in a cryogenic ethane-methane-propane liquid: Implications for Titan lake chemistry

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