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<b>Abstract</b>— <p>Titan, Saturn’s largest moon, is unique in its composition, structure, and formation history. Titan stands out among other bodies in the Solar System due to its dense nitrogen-methane atmosphere with a variety of organic compounds and a surface covered with liquid hydrocarbons. Based on cosmochemical and geophysical data, equations of state of meteoritic matter and H<sub>2</sub>O (water, water ice) models of the internal structure of Titan, composed of carbonaceous (CI/CM) and ordinary (L/LL) chondrites, with different contents of organic material (OM) of low (ρ<sub>OM</sub> ~ 1.3−1.4 g/cm<sup>3</sup>) and high (1.4 &lt; ρ<sub>OM</sub> &lt; 2.2 g/cm<sup>3</sup>) density have been constructed. In the absence of OM, three-layer models of a partially differentiated satellite with an outer water-ice shell, an intermediate rock-ice mantle, and an inner CI/CM or L/LL core may be implemented. The presence of an impurity OM with a density 1.3–1.8 g/cm<sup>3</sup> in Titan’s chondrite material provides the possibility of transition from three-layer partially differentiated models of the satellite to two-layer models of full differentiation (without rock-ice mantle)—structures free from restrictions on the melting of mantle ice. The structure of a fully differentiated Titan generally includes: a water-ice shell with a mandatory internal ocean and a layer of partially melted high-pressure V-VI ices and a central CI/CM or L/LL chondrite core with a radius of ~2100 km. Such models without OM admixture do not satisfy the conditions of conservation of mass and moment of inertia of the satellite; their consistency with geophysical constraints is due to the presence of OM in amounts of 10−22 wt % and 20−28 wt % in the CI/CM and L/LL cores, respectively. Models of Titan with high density OM (ρ<sub>OM</sub> &gt; 1.8 g/cm<sup>3</sup>) do not suggest separation of the ice and rock components, the satellite remaining partially differentiated. The estimates of the organic material content of Titan are consistent with those for a number of other icy moons of the giant planets and most Kuiper belt objects that formed beyond the snow line. This may indicate a common reservoir of precursor material in the outer Solar System and also suggests a potential genetic link between celestial bodies in this region, which requires further study.</p>

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Organic Matter in Titan: Models of Internal Structure

  • 期刊论文

  • 发表日期：

    2025年7月30日

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  • A. N. Dunaeva,
  • V. A. Kronrod,
  • O. L. Kuskov

摘要

Abstract—

Titan, Saturn’s largest moon, is unique in its composition, structure, and formation history. Titan stands out among other bodies in the Solar System due to its dense nitrogen-methane atmosphere with a variety of organic compounds and a surface covered with liquid hydrocarbons. Based on cosmochemical and geophysical data, equations of state of meteoritic matter and H2O (water, water ice) models of the internal structure of Titan, composed of carbonaceous (CI/CM) and ordinary (L/LL) chondrites, with different contents of organic material (OM) of low (ρOM ~ 1.3−1.4 g/cm3) and high (1.4 < ρOM < 2.2 g/cm3) density have been constructed. In the absence of OM, three-layer models of a partially differentiated satellite with an outer water-ice shell, an intermediate rock-ice mantle, and an inner CI/CM or L/LL core may be implemented. The presence of an impurity OM with a density 1.3–1.8 g/cm3 in Titan’s chondrite material provides the possibility of transition from three-layer partially differentiated models of the satellite to two-layer models of full differentiation (without rock-ice mantle)—structures free from restrictions on the melting of mantle ice. The structure of a fully differentiated Titan generally includes: a water-ice shell with a mandatory internal ocean and a layer of partially melted high-pressure V-VI ices and a central CI/CM or L/LL chondrite core with a radius of ~2100 km. Such models without OM admixture do not satisfy the conditions of conservation of mass and moment of inertia of the satellite; their consistency with geophysical constraints is due to the presence of OM in amounts of 10−22 wt % and 20−28 wt % in the CI/CM and L/LL cores, respectively. Models of Titan with high density OM (ρOM > 1.8 g/cm3) do not suggest separation of the ice and rock components, the satellite remaining partially differentiated. The estimates of the organic material content of Titan are consistent with those for a number of other icy moons of the giant planets and most Kuiper belt objects that formed beyond the snow line. This may indicate a common reservoir of precursor material in the outer Solar System and also suggests a potential genetic link between celestial bodies in this region, which requires further study.