201-8 Silica as a Tracer of Aqueous Alteration on Mars and Icy Moons

Session: The G.K. Gilbert Award Session: Geology of Mars, Mercury, Asteroids, and Icy Satellites in Honor of Scott Murchie

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Highly concentrated silica deposits have been found across Mars by NASA's Spirit, Curiosity, and Perseverance rovers. Orbital spectroscopy has revealed hydrous silica as a spectrally dominant surface material at many more sites, spanning a wide range of ages and indicating "that liquid water persisted later into Martian history than previous evidence had suggested" (Murchie et al., 2009). Opaline silica can preserve organic biosignatures, but this mineraloid is generally unstable over geologic timescales except in very dry environments, which Mars has overall arguably provided.

Silica can form through aqueous alteration of silicates under conditions ranging widely in temperature and pH, which fortunately leave distinct traces in the shapes and positions of silica's characteristic near-infrared spectral absorptions. I will describe several recent silica detections across Mars, whose spectral nuances and geologic contexts lead to varying interpretations of hydrothermal formation versus low-temperature weathering at a range of water-to-rock ratios.

In the outer solar system, spectra of solid surfaces are so dominated by ices, (organic?) darkening agents, and (on some bodies) salts that their presumed additional silicate components remain poorly characterized. As one exception to this, in the Saturn system Cassini detected a population of pure silica nanograins traceable to the plume erupting from Enceladus, which are thus interpreted to have formed from hydrothermal reactions at the floor of that moon's subsurface ocean. I will show potential evidence for transport of this silica to the surface of other Saturnian moons, where its further spectral characterization could enable comparison of habitable planetary environments on tidally heated icy moon interiors versus terrestrial planet surfaces.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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