Origin of Titan and its Atmosphere: New Lights from Cassini-Huygens

The origin of Titan and its atmosphere dominated by nitrogen and methane is still uncertain. A puzzling feature of the satellite's atmosphere is the non-detection of the primordial noble gases krypton and xenon by the Huygens probe, present in the atmosphere of Jupiter and presumably Saturn. The carbon monoxide to methane ratio is ∼ 10-3 in Titan's atmosphere, which also places a strong constraint on the satellite's origin, since carbon monoxide should have been more abundant than methane in the primitive nebula. Here we present a model for the origin of Titan consistent with these observations: Titan was formed from planetesimals initially produced in the primitive nebula that were partially devolatilized during their migration within Saturn's satellite-forming subnebula. In contrast with krypton and xenon which remained trapped, most of the carbon monoxide and argon was lost from icy planetesimals during their migration within the subnebula. The observed deficiency of Titan's atmosphere in krypton and xenon could result from various sequestration processes that may have occurred prior or after the satellite's completion. On the basis of our model, we predict that all regular satellites interiors to the orbit of Titan are depleted in primordial carbon monoxide and nitrogen