Stability of methane clathrate hydrates under pressure: Influence on outgassing processes of methane on Titan

Research areas:

• Intérieurs planétaires (2011 - 2016)

Year:

2010

Authors:

• M. CHOUKROUN
• Gabriel Tobie
• Christophe Sotin
• Olivier Grasset

Journal:

ICARUS

Volume:

205

Number:

2

Pages:

581-593

Month:

February

ISSN:

0019-1035

BibTex:

@article{WOS:000274599400020, author = "M. CHOUKROUN and Gabriel Tobie and Christophe Sotin and Olivier Grasset", abstract = "We have conducted high-pressure experiments in the H2O-CH4 and H2O-CH4-NH3 systems in order to investigate the stability of methane clathrate hydrates, with an optical sapphire-anvil cell coupled to a Raman spectrometer for sample characterization. The results obtained confirm that three factors determine the stability of methane clathrate hydrates: (1) the bulk methane content of the samples: (2) the presence of additional gas compounds such as nitrogen; (3) the concentration of ammonia in the aqueous solution. We show that ammonia has a strong effect on the stability of methane clathrates. For example, a 10 wt.\% NH3 solution decreases the dissociation temperature of methane clathrates by 14-25 K at pressures above 5 MPa. Then, we apply these new results to Titan{\&}#039;s conditions. Dissociation of methane clathrate hydrates and subsequent outgassing can only occur in Titan{\&}#039;s icy crust, in presence of locally large amounts of ammonia and in a warm context. We propose a model of cryomagma chamber within the crust that provides the required conditions for methane outgassing: emplacement of an ice plume triggers the melting (if solid) or heating (if liquid) of large ammonia-water pockets trapped at shallow depth, and the generated cryomagmas dissociate surrounding methane clathrate hydrates. We show that this model may allow for the outgassing of significant amounts of methane, which would be sufficient to maintain the presence of methane in Titan{\&}#039;s atmosphere for several tens of thousands of years after a large cryovolcanic event. Published by Elsevier Inc.", doi = "10.1016/j.icarus.2009.08.011", extra = "PICL", issn = "0019-1035", journal = "ICARUS", month = "FEB", number = "2", pages = "581-593", title = "{S}tability of methane clathrate hydrates under pressure: {I}nfluence on outgassing processes of methane on {T}itan", volume = "205", year = "2010", }

Abstract:

We have conducted high-pressure experiments in the H2O-CH4 and
H2O-CH4-NH3 systems in order to investigate the stability of methane
clathrate hydrates, with an optical sapphire-anvil cell coupled to a
Raman spectrometer for sample characterization. The results obtained
confirm that three factors determine the stability of methane clathrate
hydrates: (1) the bulk methane content of the samples: (2) the presence
of additional gas compounds such as nitrogen; (3) the concentration of
ammonia in the aqueous solution. We show that ammonia has a strong
effect on the stability of methane clathrates. For example, a 10 wt.\%
NH3 solution decreases the dissociation temperature of methane
clathrates by 14-25 K at pressures above 5 MPa. Then, we apply these new
results to Titan's conditions. Dissociation of methane clathrate
hydrates and subsequent outgassing can only occur in Titan's icy crust,
in presence of locally large amounts of ammonia and in a warm context.
We propose a model of cryomagma chamber within the crust that provides
the required conditions for methane outgassing: emplacement of an ice
plume triggers the melting (if solid) or heating (if liquid) of large
ammonia-water pockets trapped at shallow depth, and the generated
cryomagmas dissociate surrounding methane clathrate hydrates. We show
that this model may allow for the outgassing of significant amounts of
methane, which would be sufficient to maintain the presence of methane
in Titan's atmosphere for several tens of thousands of years after a
large cryovolcanic event. Published by Elsevier Inc.