Phase Diagram For The Methane-Ethane System And Its Implications For Titan's Lakes

By Keith Cowing
March 30, 2021
Filed under
Phase Diagram For The Methane-Ethane System And Its Implications For Titan's Lakes
Methane and ethane bands in the 2850-3000 cm-1 region in the liquid phase (95 K), normalized using Eq. 1. This demonstrates the intensity changes and Raman band shifts depending on mixing ratio.

On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in the lakes and seas.

In this study, we have combined laboratory work and modeling to refine the methane-ethane binary phase diagram at low temperatures and probe how the molecules interact at these conditions.

We used visual inspection for the liquidus and Raman spectroscopy for the solidus. Through these methods we determined a eutectic point of 71.15±0.5 K at a composition of 0.644±0.018 methane – 0.356±0.018 ethane mole fraction from the liquidus data. Using the solidus data, we found a eutectic isotherm temperature of 72.2 K with a standard deviation of 0.4 K.

In addition to mapping the binary system, we looked at the solid-solid transitions of pure ethane and found that, when cooling, the transition of solid I-III occurred at 89.45±0.2 K. The warming sequence showed transitions of solid III-II occurring at 89.85±0.2 K and solid II-I at 89.65±0.2 K. Ideal predictions were compared to molecular dynamics simulations to reveal that the methane-ethane system behaves almost ideally, and the largest deviations occur as the mixing ratio approaches the eutectic composition.

Anna E. Engle, Jennifer Hanley, Shyanne Dustrud, Garrett Thompson, Gerrick E. Lindberg, William M. Grundy, Stephen C. Tegler

Comments: Accepted to The Planetary Science Journal: 2021-03-16
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2103.15978 [astro-ph.EP] (or arXiv:2103.15978v1 [astro-ph.EP] for this version)
Submission history
From: Anna Engle
[v1] Mon, 29 Mar 2021 22:37:59 UTC (3,690 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻