Carbon isotopic enrichment in Titanʹs tholins? Implications for Titanʹs aerosols

Since the discovery of the main composition of Titanʹs atmosphere, many laboratory experiments have been carried out to reproduce its chemical evolution, particularly the formation of organic haze particles found throughout this atmosphere. Some of these simulations have produced solid products—referred to as Titanʹs tholins—that are assumed to have properties similar to those of Titanʹs aerosols. In the present work, we focus on the possible isotopic fractionation of carbon during the processes involved in the formation of Titanʹs tholins. Initial 12C/13C isotopic ratios measured on tholins made in the laboratory using cold plasma discharges are presented. Measurements of isotopic enhancement in 13C (δ13C), both on tholins and on the initial gas mixture (N2:CH4 (98:2)) used to produce them do not show any clear deficit or enrichment in 13C relative to 12C in the lab-made tholins compared to the initial gas mixture. Preliminary data recovered from the Aerosol Collector Pyrolyzer (ACP) experiment of the Huygens probe suggests that Titanʹs aerosols may also be exempt of carbon isotopic enrichment. This observation creates possibilities for deeper analysis of ACP experiment data.