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Oxygen Ion Irradiation of Tholins: Implications for the Incorporation of Oxygen into Aerosols in Titan’s Atmosphere

Year: 2026

Type: article

Abstract: Heavy molecules reaching several thousand atomic mass units and O + ions have been detected in Titan’s atmosphere and Saturn’s magnetosphere, respectively. The heavy molecules are attributed to potentially nitrogenous polycyclic aromatic hydrocarbons (PANH), while the energetic O + ions deposit in Titan’s upper atmosphere and may be expected to alter the structure and chemical composition of these macromolecules by implantation and incorporation. This process was studied by irradiating thin-film tholin samples with either 18 O q + or 20 Ne q + ions at different energies (35 and 70 keV), temperatures (150 and 300 K), and fluences (0.34–2.28 × 10 15 ions cm −2 ). Ex situ elemental analysis isotope ratio mass spectrometry (EA-IRMS) was used to determine the stable oxygen isotope composition of both the soluble and insoluble fractions of the irradiated samples, assessing ion-induced oxygen incorporation. The results demonstrate an increase in 18 O for all samples irradiated with O ions, whereas nonirradiated and Ne-irradiated samples show no such enhancement. This confirms that oxygen implantation into tholins is possible. The fraction of incident oxygen ions incorporated into the tholins ranges from approximately 4%–27%, depending on sample properties, solubility fractions, and film thickness. These findings provide important insights into the role of energetic oxygen species in modifying Titan’s organic aerosols. The incorporation of oxygen has implications for the formation of oxygenated molecules with astrobiological interest.

Source: The Planetary Science Journal

DOI: 10.3847/psj/aea6d6