Partial dissociation of clathrate hydrates in the presence of ammonia: a potential mechanism for replenishing Titan's atmospheric methane
Abstract
Titan's rich atmospheric organic chemistry and hydrocarbon cycle are inherently driven by the photolysis of methane and nitrogen and their recombination into higher-degree hydrocarbons and other organic molecules. However, Titan's present-day methane atmospheric inventory would only sustain this open cycle for 30-100 My, requiring methane replenishment processes to preserve the current atmospheric chemical engine over long geologic timescales. Methane clathrate hydrates have long been considered as a likely storage medium in Titan's interior. Additionally, the expected thermal state of Titan's surface and icy shell is within the stability field of these compounds, such that they would not normally be able to dissociate and release their trapped methane.
This stability is affected by the presence of ammonia, which acts as an "antifreeze", altering the phase behavior of methane clathrate hydrates. These changes in stability are poorly understood. Accordingly, we have sought to better understand how ammonia interacts with clathrate hydrates via a detailed experimental investigation of phase behavior in the ternary H2O-NH3-THF system using micro-Raman spectroscopy, differential scanning calorimetry, and synchrotron powder X-ray diffraction. We will present a selection of these results, and discuss their implication in terms of geologic settings and processes where clathrate hydrates may dissociate (at least partially) and release their trapped methane. By combining thermal modeling of Titan's near surface and the phase behavior of clathrates derived from the aforementioned experiments, we test whether a partial dissociation of the clathrate reservoir can occur, and to what extent. We then assess whether this potential methane release mechanism could sustain the presence of methane in the atmosphere over geologic timescales.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P21C..03C
- Keywords:
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- 5210 Planetary atmospheres;
- clouds;
- and hazes;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6281 Titan;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS