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Cold traps on Ceres based on refined shape models

Presentation #102.08 in the session Asteroids: Objects of Interest (Oral Presentation)

Published onOct 23, 2023
Cold traps on Ceres based on refined shape models

Dwarf planet Ceres hosts perennially shadowed regions (PSRs) [1-4]. Due to the high sensitivity of the Dawn cameras, bright ice deposits were discovered in a fraction of the PSRs. The axis tilt (currently 4.02°) oscillates between 2° and almost 20° with a period of 24.5 ky, which changes the extent of PSRs over time [4]. Stereophotoclinometry (SPC) was used to create improved shape models for nine PSR-hosting craters based on Framing Camera images [5]. To use data from secondary illumination, an experimental procedure was developed whereby data was extracted from shadowed areas with an illumination from the anti-Sun azimuth.

Shadows were calculated by ray-tracing over a solar day at summer solstice using the model described in Ref. [6]. The PSR areas often differ from those obtained using a global shape model [4]. Unlike previous analysis, no PSRs remain among the study sites at the maximum axis tilt of 20°, so the ice deposits must be of recent origin. The axis tilt is currently increasing from its periodic minimum of 2° and the most recent obliquity maximum was 13.9 ky ago [4]. A massive delivery of water to the polar regions before about 6 ky ago would have resulted in smaller or no ice deposits, and a more recent delivery would have resulted in larger ice deposits. The remarkably young age of the ice deposits implies delivery is frequent.

Equilibrium surface temperatures were calculated using a view factor matrix and solutions of the radiosity equation for infrared and visible wavelengths [6]. Areas with a maximum equilibrium temperature of less than 80 K are negligible in size. The cold traps in the north polar region of Ceres are relatively warm due to the high axis tilt and the absence of significant cold traps very close to the north pole. No hypervolatiles (such as NH3·H2O, CO2, or NH3) are expected to have remained in Ceres’s cold traps.

References: [1] Hayne P.O. & Aharonson O. (2015) JGR 120, 1567. [2] Schorghofer N. et al. (2016) GRL 43, 6783. [3] Platz T. et al. (2016) Nature 1, 0007. [4] Ermakov A. et al. (2017) GRL 44, 2652. [5] Sierks H. et al. (2011) Space Sci. Rev. 163, 263. [6] Potter S. F. et al. (2023) J. Comp. Phys. X, in press, arXiv:2209.07632.

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