Organic Content of Titan’s Sub-Surface Ocean: Constraints from Chondrites

Abstract:

Heating of accreted organic material in Titan’s interior has been suggested as a possible source for atmospheric N2 and CH4 [1] via outgassing [2,3]. The original organic material may be analogous in composition to insoluble organic matter (IOM) from chondritic meteorites. If Titan’s atmospheric volatiles include hydrothermal products of IOM degradation, then there may be an analogous flux to Titan’s ocean of any organic material produced through the same process. Previous experimental work simulating hydrothermal alteration of chondritic IOM resulted in production of intermediate-mass organic products [4,5]. Here, we consider the solubility of organic products of IOM decomposition.

We consider two different end-member organic abundances: a “cometary” example with 45 weight percent organics in rock, and a “chondritic” abundance with 4 weight percent organics. We also consider water-to-rock (W/R) ratios from 0.5 to 10 to represent different possible environments in Titan’s interior, where W/R = 0.5 may represent the outer layers of the rocky core, and W/R = 10 may represent mixing at the water-rock interface. In general, preliminary results suggest that most organic products would be under-saturated in Titan’s ocean for all conditions, with the exception of aromatic compounds larger than three rings. We calculate summed dissolved organic carbon (DOC) abundances that range from 3 to 530 μM. Terrestrial oceanic DOC is typically 10s of μM [6], which would be matched by a cometary organic abundance with W/R = 5-10, or chondritic abundance with W/R = 0.5-1.

[1] Miller et al. (2019) Astrophysical Journal

[2] Tobie et al. (2006) Nature

[3] Glein (2015) Icarus

[4] Yabuta et al. (2007) Meteoritics & Planetary Science

[5] Sephton et al. (2004) Geochimica et Cosmochimica Acta

[6] Ogawa and Tanoue (2003) Journal of Oceanography