Astrochemistry

The Equilibrium Vapor Pressures of Ammonia and Oxygen Ices at Outer Solar System Temperatures

By Keith Cowing
Status Report
astro-ph.EP
March 19, 2024
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The Equilibrium Vapor Pressures of Ammonia and Oxygen Ices at Outer Solar System Temperatures
Published laboratory studies and extrapolated values of equilibrium vapor pressures. Adapted from Fray and Schmitt (2009), dotted lines indicate selected extrapolations from published studies; thick lines represent previously published laboratory data; circles show triple points; a square on the O2 line indicates the transition point between beta and gamma crystalline phases (the transition point between alpha and beta is below this range). A thick dotted line at 90 K represents the approximate highest temperature of the Uranian satellites. Many studies have been carried out at higher temperatures than are relevant for the Uranian system, especially ammonia, as annotated in the plot. — astro-ph.EP

Few laboratory studies have investigated the vapor pressures of the volatiles that may be present as ices in the outer solar system; even fewer studies have investigated these species at the temperatures and pressures suitable to the surfaces of icy bodies in the Saturnian and Uranian systems (<100 K, <10−9 bar).

This study adds to the work of Grundy et al. (2024) in extending the known equilibrium vapor pressures of outer solar system ices through laboratory investigations at very low temperatures. Our experiments with ammonia and oxygen ices provide new thermodynamic models for these species’ respective enthalpies of sublimation.

We find that ammonia ice, and to a lesser degree oxygen ice, are stable at higher temperatures than extrapolations in previous literature have predicted. Our results show that these ices should be retained over longer periods of time than previous extrapolations would predict, and a greater amount of these solids is required to support observation in exospheres of airless bodies in the outer solar system.

B.P. Blakley, Will M. Grundy, Jordan K. Steckloff, Sugata P. Tan, Jennifer Hanley, Anna E. Engle, Stephen C. Tegler, Gerrick E. Lindberg, Shae M. Raposa, Kendall J. Koga, Cecilia L. Thieberger

Comments: 29 pages, 9 figures, to be published in Planetary and Space Science
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2403.09917 [astro-ph.EP] (or arXiv:2403.09917v1 [astro-ph.EP] for this version)
Related DOI:
https://doi.org/10.1016/j.pss.2024.105863
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Submission history
From: B.P. Blakley
[v1] Thu, 14 Mar 2024 23:26:26 UTC (577 KB)
https://arxiv.org/abs/2403.09917

Astrobiology, Astrochemistry,

Keith Cowing

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) 🖖🏻

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