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Sure the red cap is fascinating, but what of Charon’s gray cloak?

Presentation #303.04 in the session Pluto through the Ages.

Published onOct 20, 2022
Sure the red cap is fascinating, but what of Charon’s gray cloak?

While it is difficult to not be mesmerized by Charon’s red polar cap, the subtle grey tone masking the lower latitude regions [1-6] is equally interesting, beseeching an explanation. Recent results from laboratory experiments combined with exospheric modeling [7, 8] provide insightful clues to the origin of Charon’s colorful landscape. Dynamic interplanetary medium Lyman-α (IPM Ly-α) photolysis of Plutonian methane accreting at seasonally-varying rates imprints a latitude-dependent compositional complexity gradient onto the winter hemisphere [7]. The photolyzed polar frost is primarily ethane while the lower latitudes harbor the more complex, less volatile, refractories. We posit that solar wind (SW) processing following spring sunrise converts polar ethane to tholin-like refractories which may impart the red hue to the Mordor Macula region. SW radiolysis could also dehydrogenate the already-complex photoproducts [9-13] at lower latitudes reducing them to carbon-rich species likely responsible for Charon’s gray shade. We will estimate the relative abundance of this neutral gray absorber needed to explain Charon’s low visible albedo [14, 15] and assess the timescales required to accumulate such abundances through successive cycles of IPM photolysis and SW radiolysis.

[1] Stern et al., Science, 350, 6258, 2015 [2] Cruikshank et al., Icarus, 246, 82-92, 2015 [3] Grundy et al., Science, 351, 6279, 2016 [4] Grundy et al., Nature, 539, 65-68, 2016 [5] Protopapa et al., in The Pluto System after New Horizons, 433-456, 2021 [6] Howett et al., in The Pluto System after New Horizons, 413-432, 2021 [7] Raut et al., Science Advances, 8, 24, 2022 [8] Teolis et al., Geophysical Research Letters, 49, 8, 2022 [9] Compagnini et al., Carbon, 47, 6, 2009 [10] Foti et al., NIM B, 24-25, 522-525, 1987 [11] Brown et al., NIM B: 24-35, 1, 512-516, 1987 [12] Thompson et al., JGR: Space Physics, 92, A13, 14933-14947, 1987 [13] Moore, M. H. and Hudson R.L., Icarus, 135, 2, 518-527, 1998 [14] Buratti et al., Astrophysical Journal Letters, 874, L3, 2019 [15] Tholen, D.J. and Buie, M. W., Astronomical Journal, 96, 1977-1982, 1989.

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