Properties and Behavior of the Acetonitrile–Acetylene Co-Crystal under Titan Surface Conditions

Cable, Morgan L.; Vu, Tuan; Malaska, Michael J.; Maynard-Casely, Helen E.; Choukroun, Mathieu; Hodyss, Robert

doi:10.1021/acsearthspacechem.0c00129

Cited by 20 publications

(29 citation statements)

References 78 publications

(139 reference statements)

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“…In addition to these two structures, numerous acetylenebearing crystalline materials have been discovered, including clathrate hydrates (Kirchner et al, 2004;Vu et al, 2019) and co-crystals with a host of small molecular species (Busker et al, 2008;Boese et al, 2009;Kirchner et al, 2010;Preston & Signorell, 2012). Several of these co-crystals have been demonstrated to form readily under Titan-relevant conditions via Raman microscopy, namely C 2 H 2 -NH 3 (Cable et al, 2018), C 2 H 2 -C 4 H 10 (Cable et al, 2019) and C 2 H 2 -CH 3 CN (Cable et al, 2020). The C 2 H 2 -NH 3 co-crystal is of particular interest as a putative Titan mineral as it forms within minutes from the interaction between solid C 2 H 2 and solid NH 3 at 90 K and remains stable up until about 120 K, even when exposed to simulated pluvial and fluvial events containing liquid methane, ethane and propane (Cable et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Anisotropic thermal expansion of the acetylene–ammonia co-crystal under Titan's conditions

Maynard-Casely

Cable

et al. 2020

J Appl Cryst

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Acetylene and ammonia are known to form a stable orthorhombic co-crystal under the surface conditions of Saturn's moon Titan (1.5 bar = 150 kPa, 94 K). Such a material represents a potential new class of organic minerals that could play an important role in Titan's geology. In this work, the thermal expansion of this co-crystalline system has been derived from in situ powder X-ray diffraction data obtained between 85 and 120 K. The results indicate significant anisotropy, with the majority of the expansion occurring along the c axis (∼2% over the temperature range of interest). Rietveld refinements reveal little change to the structure compared with that previously reported by Boese, Bläser & Jansen [J. Am. Chem. Soc. (2009), 131, 2104–2106]. The expansion is consistent with the alignment of C—H...N interactions along the chains in the a and b axes, and weak intermolecular bonding in the structural layers along the c axis.

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Section: Introductionmentioning

confidence: 99%

Anisotropic thermal expansion of the acetylene–ammonia co-crystal under Titan's conditions

Maynard-Casely

Cable

et al. 2020

J Appl Cryst

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“…Finally, concerning the interaction solid-liquid, we cannot exclude the existence of more complex, and mainly unknown, physico-chemical processes leading to the formation of somewhat exotic species such as the co-crystals recently revealed by laboratory studies (Vu et al 2014(Vu et al , 2020aCable et al 2014Cable et al , 2019Cable et al , 2020McConville et al 2020;Czaplinski et al 2020).…”

Section: Ar Kr Xementioning

confidence: 96%

Vertical compositional variations of liquid hydrocarbons in Titan’s alkanofers

Cordier

Bonhommeau

et al. 2021

A&A

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Context. According to clues left by the Cassini mission, Titan, one of the two Solar System bodies with a hydrologic cycle, may harbor liquid hydrocarbon-based analogs of our terrestrial aquifers, referred to as “alkanofers”. Aims. On the Earth, petroleum and natural gas reservoirs show a vertical gradient in chemical composition, established over geological timescales. In this work, we aim to investigate the conditions under which Titan’s processes could lead to similar situations. Methods. We built numerical models including barodiffusion and thermodiffusion (Soret’s effect) in N2+CH4+C2H6 liquid mixtures, which are relevant for Titan’s possible alkanofers. Our main assumption is the existence of reservoirs of liquids trapped in a porous matrix with low permeability. Results. Due to the small size of the molecule, nitrogen seems to be more sensitive to gravity than ethane, even if the latter has a slightly larger mass. This behavior, noticed for an isothermal crust, is reinforced by the presence of a geothermal gradient. Vertical composition gradients, formed over timescales of between a fraction of a mega-year to several tens of mega-years, are not influenced by molecular diffusion coefficients. We find that ethane does not accumulate at the bottom of the alkanofers under diffusion, leaving the question of why ethane is not observed on Titan’s surface unresolved. If the alkanofer liquid was in contact with water-ice, we checked that N2 did not, in general, impede the clathration of C2H6, except in some layers. Interestingly, we found that noble gases could easily accumulate at the bottom of an alkanofer.

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“…Of course, the straightforward approach described here would deserve a more detailed study. Finally, concerning the interaction solid-liquid, we cannot exclude the existence of more complex, and mainly unknown, physico-chemical processes leading to the formation of somewhat exotic species such as the co-crystals recently revealed by laboratory studies (Vu et al 2014(Vu et al , 2020aCable et al 2014Cable et al , 2019Cable et al , 2020McConville et al 2020;Czaplinski et al 2020).…”

Section: Liquid-solid Interactionmentioning

confidence: 97%

Vertical compositional variations of liquid hydrocarbons in Titan's alkanofers

Cordier,

Bonhommeau,

et al. 2021

Preprint

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Context. According to clues left by the Cassini mission, Titan, one of the two Solar System bodies with a hydrologic cycle, may harbor liquid hydrocarbon-based analogs of our terrestrial aquifers, referred to as "alkanofers". Aims. On the Earth, petroleum and natural gas reservoirs show a vertical gradient in chemical composition, established over geological timescales. In this work, we aim to investigate the conditions under which Titan's processes could lead to similar situations. Methods. We built numerical models including barodiffusion and thermodiffusion (Soret's effect) in N 2 +CH 4 +C 2 H 6 liquid mixtures, which are relevant for Titan's possible alkanofers. Our main assumption is the existence of reservoirs of liquids trapped in a porous matrix with low permeability. Results. Due to the small size of the molecule, nitrogen seems to be more sensitive to gravity than ethane, even if the latter has a slightly larger mass. This behavior, noticed for an isothermal crust, is reinforced by the presence of a geothermal gradient. Vertical composition gradients, formed over timescales of between a fraction of a mega-year to several tens of mega-years, are not influenced by molecular diffusion coefficients. We find that ethane does not accumulate at the bottom of the alkanofers under diffusion, leaving the question of why ethane is not observed on Titan's surface unresolved. If the alkanofer liquid was in contact with water-ice, we checked that N 2 did not, in general, impede the clathration of C 2 H 6 , except in some layers. Interestingly, we found that noble gases could easily accumulate at the bottom of an alkanofer.

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Properties and Behavior of the Acetonitrile–Acetylene Co-Crystal under Titan Surface Conditions

Cited by 20 publications

References 78 publications

Anisotropic thermal expansion of the acetylene–ammonia co-crystal under Titan's conditions

Anisotropic thermal expansion of the acetylene–ammonia co-crystal under Titan's conditions

Vertical compositional variations of liquid hydrocarbons in Titan’s alkanofers

Vertical compositional variations of liquid hydrocarbons in Titan's alkanofers

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