Removal of Titan's Atmospheric Noble Gases by their Sequestration in Surface Clathrates

TL;DR

This paper explains the absence of heavy noble gases in Titan's atmosphere by proposing that surface conditions favor the formation of clathrates which sequester these gases, reducing their atmospheric presence.

Contribution

It introduces a new hypothesis that surface clathrates formed from cryovolcanic activity can trap heavy noble gases, accounting for their scarcity in Titan's atmosphere.

Findings

Heavy noble gases are likely sequestered in surface clathrates.

A few meters of clathrate crust could remove all heavy noble gases.

Cryovolcanic activity supplies water ice for clathrate formation.

Abstract

A striking feature of the atmosphere of Titan is that no heavy noble gases other than argon were detected by the Gas Chromatograph Mass Spectrometer (GCMS) aboard the Huygens probe during its descent to Titan's surface in January 2005. Here we provide an explanation of the mysterious absence or rarity of these noble gases in Titan's atmosphere: the thermodynamic conditions prevailing at the surface-atmosphere interface of the satellite allow the formation of multiple guest clathrates that preferentially store some species, including all heavy noble gases, over others. The clean water ice needed for formation of these clathrates could be delivered by successive episodes of cryovolcanic lavas that have been hypothesized to regularly cover the surface of Titan. The formation of clathrates in the porous lavas and their propensity for trapping Ar, Kr and Xe would progressively remove these species from the atmosphere of Titan over its history. In some circumstances, a global clathrate crust with an average thickness not exceeding a few meters could be sufficient on Titan for a complete removal of the heavy noble gases from the atmosphere.