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Low-temperature aqueous alteration of cometary rocks: Applications to potential ocean worlds of the Uranian system

Presentation #509.09 in the session Icy Moons Interior and Ice Shell (Oral Presentation)

Published onOct 23, 2023
Low-temperature aqueous alteration of cometary rocks: Applications to potential ocean worlds of the Uranian system

Uranus possesses a diverse satellite system, including the five major moons Miranda, Ariel, Umbriel, Titania and Oberon. Among them, Miranda and Ariel show extensive evidence for widespread tectonism, potentially associated with cryovolcanic activity [1,2]. Recent telescopic observations suggest the presence of ammonia-bearing species, consistent with geologically recent replenishment events [3,4]. Theoretical models also suggest that subsurface liquid water oceans could be maintained just by radiogenic heating in Titania and Oberon [5,6]. These findings introduce numerous questions, such as what ocean signatures could be detected in a future Uranus mission. However, details on the effects of liquid water on the composition of those satellites remain little explored. Here, we modeled the aqueous alteration of Fe-Na-Ca-Mg-Si-Al-C-O-N-S-Cl system, focusing on the low-temperature regime. We generate a new thermodynamics database with minerals that are relevant to the Outer Solar System but have not been considered extensively (i.e., ammonium-bearing/clay minerals). Assuming that the initial oxidation state of rock is determined by FeS/FeO, the fluid becomes alkaline at equilibrium (pH~9.3), and significant amount of aqueous H2 (~ 3 x 10-5 molal) is also produced. The low-temperature and alkaline environment is also favorable for the formation of ammonium-bearing minerals. If the detected ammonia on some Uranian moons is indeed from their subsurface oceans, it suggests that water-rock interaction has not yet been possessed extensively inside their interiors. This has implications for the preservation of subsurface liquid water (as significant amounts of ammonia are still present as anti-freezers) and the potential cycling of redox species and other nutrients to sustain habitability. [1] Beddingfield. C. B and Cartwright R. J. (2020), Icarus, 343, 113687. [2] Schenk, P. M. and Moore, J. M. (2020), PTRSA, 378. [3] Cartwright, R. J. et al. (2018), Icarus, 314, 210-231. [4] Cartwright, R. J. et al. (2020), ApJL, 898(1), 2. [5] Hussmann, H. et al. (2006), Icarus, 185(1), 258-273. [6] Bierson, C & Nimmo, F. (2022), Icarus, 373, 114776

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