Evolution of Titan and implications for its hydrocarbon cycle

Abstract

Measurements of the carbon and nitrogen isotopic ratios as well as the detection of 40 Ar and 36 Ar by the gas chromatograph mass spectrometer (GCMS) instrument on board the Huygens probe have provided key constraints on the origin and evolution of Titan's atmosphere, and indirectly on the evolution of its interior. Those data combined with models of Titan's interior can be used to determine the story of volatile outgassing since Titan's formation. In the absence of an internal source, methane, which is irreversibly photodissociated in Titan's stratosphere, should be removed entirely from the atmosphere in a time-span of a few tens of millions of years. The episodic destabilization of methane clathrate reservoir stored within Titan's crust and subsequent methane outgassing could explain the present atmospheric abundance of methane, as well as the presence of argon in the atmosphere. The idea that methane is released from the interior through eruptive processes is also supported by the observations of several cryovolcanic-like features on Titan's surface by the mapping spectrometer (VIMS) and the radar on board Cassini. Thermal instabilities within the icy crust, possibly favoured by the presence of ammonia, may explain the observed features and provide the conditions for eruption of methane and other volatiles. Episodic resurfacing events associated with thermal and compositional instabilities in the icy crust can have major consequences on the hydrocarbon budget on Titan's surface and atmosphere.

Atmospheric Circulation, Chemistry, and Infrared Spectra of Titan-like Exoplanets around Different Stellar Types

“…Titan's atmospheric methane, however, has a finite lifetime of tens of millions of years (Yung et al 1984), and there is evidence that the current carbon inventory is only approximately half a billion years old (Mandt et al 2012) whereas the nitrogen is essentially primordial (Niemann et al 2005). It is therefore possible that Titan-like nitrogen atmospheres can exist for long periods largely devoid of methane, punctuated by episodic replenishment (Tobie et al 2006(Tobie et al , 2009. "Snowball" Titan states would exhibit different atmospheric structure (Lorenz et al 1997b;Charnay et al 2014), as well as very different photochemistry (Wong et al 2015), potentially with different dependences on host stellar spectra.…”

Is Titan's shape caused by its meteorology and carbon cycle?

“…Calculations show that the total amounts of hydrocarbons in the lakes would be in the range 1,000 to 4,000 GT, which would correspond to some hundreds of thousands of years at the precipitation rate of 50 μm/Titan year at latitudes greater than 60–70° [ Griffith et al , 2006; Rannou et al , 2006]. However, much more ethane is expected to have precipitated on Titan throughout its history and the missing ethane must be trapped in the subsurface [ Mousis and Schmitt , 2008; Tobie et al , 2009]. In this paper we investigate the substitution of methane by ethane in the clathrate phase within the crust as seen in laboratory experiments [ Murshed and Kuhs , 2007; Murshed et al , 2010] and the implications of this process on the isotatic subsidence of the poles and on the replenishment of Titan's atmospheric methane.…”

Modeling nitrogen and methane with ethane and propane gas hydrates at low temperatures (173–290K) with applications to Titan

“…There have been numerous studies in recent years dealing with the chemistries of subsurface fluids on Titan, especially with respect to (NH 4 ) 2 SO 4 , NH 3 , and CH 4 •6H 2 O (Osegovic and Max, 2005;Atreya et al, 2006;Fortes et al, 2007;Spencer and Grinspoon, 2007;Grindrod et al, 2008;Tobie et al, 2009;Fortes and Choukroun, 2010;Sohl et al, 2010;Norman and Fortes, 2011;Fortes, 2012;Marion et al, 2012Marion et al, , 2014Vance et al, 2012;Glein, 2015). Cassini has discovered a subsurface water ocean on Titan (less et al, 2012), which was previously predicted by many interior models (Fortes, 2000;Baker et al, 2005;Tobie et al, 2005;Fortes et al, 2007;Lorenz et al, 2008;Sotin and Tobie, 2008;Tobie et al, 2009;Sohl et al, 2010).…”

“…Cassini has discovered a subsurface water ocean on Titan (less et al, 2012), which was previously predicted by many interior models (Fortes, 2000;Baker et al, 2005;Tobie et al, 2005;Fortes et al, 2007;Lorenz et al, 2008;Sotin and Tobie, 2008;Tobie et al, 2009;Sohl et al, 2010). The ocean maybe close to 50 km beneath the surface and for much of the past may have been within 10-20 km (Tobie et al, 2005).…”