Experimental heating of complex organic matter at Titan’s interior conditions supports contributions to atmospheric N2 and CH4

Abstract

Titan’s abundant atmospheric N₂ and CH₄ gases are notable characteristics of the moon that may help constrain its origin and evolution. Previous work suggests that atmospheric CH₄ is lost on geologically short timescales and may be replenished from an interior source. Isotopic and noble gas constraints indicate that N₂ may derive from a mixture of NH₃ ice and heating of organic matter. Here, we report experimental results from hydrothermal alteration of insoluble organic matter from the Murchison meteorite and analog insoluble organic matter at temperatures and pressures that are relevant to Titan’s interior. Our results indicate both CH₄ and CO₂ are formed, with the ratio between the two depending on a multitude of factors, particularly temperature and, to a lesser degree, the dielectric constant of water and carbonyl abundance in the starting material. Sufficient CH₄ is produced to source Titan’s atmospheric reservoir if temperatures are greater than 250 °C. Nitrogen is volatilized, primarily in the form of NH₃, in sufficient abundances to source at least 50 % of Titan’s atmospheric N₂. The isotopic characteristics of volatilized material relative to the starting organics are consistent with current constraints for the nature of the accreted complex organics and Titan’s evolved atmosphere.