T144 The Big Picture from Small Bodies: Dwarf Planets, Asteroids, and Comets

Monday, 23 September 2019
1:30 PM - 5:30 PM
Room 232BC, North Building

SURFICIAL EVIDENCE FOR THE VARIED SOURCES OF FACULAE-FORMING BRINES IN OCCATOR CRATER

Paper number: T144-5
Program: Technical Sessions
Time: 2:25 PM – 2:40 PM

Authors

Abstract

Dawn observed enigmatic faculae (bright regions) in Occator crater (Russell+, 2016). The faculae are mostly composed of sodium carbonate and ammonium chloride, consistent with the remnants of brines sourced in the subsurface (De Sanctis+, 2016; Raponi+, 2019). Low elliptical orbits provided up to ~3 m/pix Framing Camera images of Occator from as low as ~35 km. We use this data to create a new, highest resolution geologic map of Occator and its faculae. We find that the faculae were emplaced via brine effusion: hydrothermal deposits were emplaced ballistically and as flows, which originated from numerous localized sources of brine that were unresolved in previous data. Many characteristics of the faculae resemble those of terrestrial/Martian hydrothermal deposits (Osinski+, 2013), including an association with fractures and the crater center (which would remain hottest for the longest time). A complex hydrologic plumbing system of fracture and hydrologic networks can explain the deposition of Pasola Facula (PF) on a ledge about the central pit, which contains Cerealia Facula (CF). Both CF and PF were sourced in an impact-induced melt chamber, which is predicted to have formed under the Occator's center (Bowling+, 2019). Our mapping shows that the availability of the faculae-forming brines varied on short spatial scales, and that the system was often brine-limited. Vinalia Faculae (VF) are located in the eastern crater floor, too far from the crater center to be sourced in the impact-induced melt chamber. Instead, VF could be sourced by a deep, long-lived brine reservoir, which existed before the Occator-forming impact and is predicted from thermal modeling (Castillo+, 2019). Surficial evidence for this hypothesis is that VF are significantly thinner and less voluminous than CF. This is consistent with the VF-forming brines, sourced in the deep brine reservoir, taking a longer and more difficult path to the surface than the CF-forming brines, which were locally fed from the shallower impact-inducted melt chamber. In both cases, pathways to the surface were opened by the prevalent impact-induced fracturing throughout the crater (Raymond+, submitted). Part of this work is being carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-339505

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