A primordial origin for the atmospheric methane of Saturn's moon Titan

Abstract

The origin of Titan's atmospheric methane is a key issue for understanding the origin of the Saturnian satellite system. It has been proposed that serpentinization reactions in Titan's interior could lead to the formation of the observed methane. Meanwhile, alternative scenarios suggest that methane was incorporated in Titan's planetesimals before its formation. Here, we point out that serpentinization reactions in Titan's interior are not able to reproduce the deuterium over hydrogen (D/H) ratio observed at present in methane in its atmosphere, and would require a maximum D/H ratio in Titan's water ice 30% lower than the value likely acquired by the satellite during its formation, based on Cassini observations at Enceladus. Alternatively, production of methane in Titan's interior via radiolytic reactions with water can be envisaged but the associated production rates remain uncertain. On the other hand, a mechanism that easily explains the presence of large amounts of methane trapped in Titan in a way consistent with its measured atmospheric D/H ratio is its direct capture in the satellite's planetesimals at the time of their formation in the solar nebula. In this case, the mass of methane trapped in Titan's interior can be up to 1,300 times the current mass of atmospheric methane.

Accepted for publication in Icarus

References in corpus (4)

• Determination of the minimum masses of heavy elements in the envelopes of Jupiter and Saturn
• Clathration of Volatiles in the Solar Nebula and Implications for the Origin of Titan's atmosphere
• Constraints from deuterium on the formation of icy bodies in the Jovian system and beyond
• Photochemical enrichment of deuterium in Titan's atmosphere: new insights from Cassini-Huygens

Cited by in corpus (8)

• Methane clathrates in the Solar System
• An experimental study of the surface formation of methane in interstellar molecular clouds
• Laboratory Studies of Methane and Its Relationship to Prebiotic Chemistry
• Moderate D/H Ratios in Methane Ice on Eris and Makemake as Evidence of Hydrothermal or Metamorphic Processes in Their Interiors: Geochemical Analysis
• Measurement of CH${}_3$D on Titan at Submillimeter Wavelengths
• Observations of the D/H ratio in Methane in the atmosphere of Saturn's moon, Titan - where did the Saturnian system form?
• Radiation-induced D/H Exchange Rate Constants in Aliphatics Embedded in Water Ice
• Noble gas depletion on Titan: Clathrate sequestration during the open ocean phase