Methane Clathrates in the Solar System

Abstract

ABSTRACT.We review the reservoirs of methane clathrates that may exist in the different bodies of the Solar System. Methane was formed in the interstellar medium prior to having been embedded in the protosolar nebula gas phase. This molecule was subsequently trapped in clathrates that formed from crystalline water ice during the cooling of the disk and incorporated in this form in the building blocks of comets, icy bodies, and giant planets. Methane clathrates may play an important role in the evolution of planetary atmospheres. On Earth, the production of methane in clathrates is essentially biological, and these compounds are mostly found in permafrost regions or in the sediments of continental shelves. On Mars, methane would more likely derive from hydrothermal reactions with olivine-rich material. If they do exist, martian methane clathrates would be stable only at depth in the cryosphere and sporadically release some methane into the atmosphere via mechanisms that remain to be determined. In the case of Titan, most of its methane probably originates from the protosolar nebula, where it would have been trapped in the clathrates agglomerated by the satellite's building blocks.Methane clathrates are still believed to play an important role in the present state of Titan.Their presence is invoked in the satellite's subsurface as a means of replenishing its atmosphere with methane via outgassing episodes. The internal oceans of Enceladus and Europa also provide appropriate thermodynamic conditions that allow formation of methane clathrates. In turn, these clathrates might influence the composition of these liquid reservoirs. Finally, comets and Kuiper Belt Objects might have formed from the agglomeration of clathrates and pure ices in the nebula. The methane observed in comets would then result from the destabilization of clathrate layers in the nuclei concurrent with their approach to perihelion.Thermodynamic equilibrium calculations show that methane-rich clathrate layers may exist on Pluto as well.

Methane bursts as a trigger for intermittent lake-forming climates on post-Noachian Mars

“…Early Mars had active magmatism, initially high geothermal heat flow, likely a large water inventory 97 , and a basaltic/ultramafic crust. Therefore, the amount of CH4 produced by serpentinization early in Mars history is potentially very large [98][99] . Whether this CH4-production potential was realized depends on details of catalyst distribution and crustal permeability, which are poorly known even for Earth.…”

Geochemistry, thermal evolution, and cryovolcanism on Ceres with a muddy ice mantle

“…Under conditions producing methane‐rich solutions, methane clathrates could form, as most of the subsurface liquid colder than 300 K lies in their stability field [ Mousis et al , ]. As thermodynamic data for methane clathrates were not included in our geochemical calculations, we cannot predict at this time whether clathration occurs.…”

Tetrahedral hydrocarbon nanoparticles in space: X-ray spectra

“…Methane molecules are present in Earth's atmosphere where they could interact with scattered solar and auroral X-rays. CH4 was also observed in several extraterrestrial sources (Mousis et al 2015). For example, the presence of methane was confirmed by Cassini spectrometers on the Saturn's largest moon Titan (Niemann et al 2005), as well as in the Enceladus plume (Waite et al 2006).…”