Pwyll and Manannán Craters as a Laboratory for Constraining Irradiation Timescales on Europa
We examine high spatial resolution Galileo/NIMS observations of the young (~1 My – 20 My) impact features, Pwyll and Manannán craters, on Europa’s trailing hemisphere in an effort to constrain irradiation timescales.
We characterize their composition using a linear spectral modeling analysis and find that both craters and their ejecta are depleted in hydrated sulfuric acid relative to nearby older terrain.
(a) Enhanced color image constructed from Galileo/SSI images of Pwyll crater and the surrounding regions on Europa’s trailing hemisphere. The dark, red crater and proximal ejecta are seen near the center of the image surrounded by an extensive bright ejecta blanket with rays extending over a thousand kilometers from the impact site. This bright ice-rich ejecta stands in stark contrast to the darker, reddish surface of Europa’s trailing hemisphere. This image is from NASA/JPL/University of Arizona. (b) Galileo/SSI image of Pwyll crater, taken with the clear filter. This image is from NASA/JPL/DLR. (c) Galileo/SSI image of Manann´an crater taken with the clear filter. This image is from NASA/JPL/DLR. In all three panels, north is towards the top of the image. For panels (b) and (c), the sun illuminates the surface from the right. — astro-ph.EP
This suggests that the radiolytic sulfur cycle has not yet had enough time to build up an equilibrium concentration of H2SO4, and places a strong lower limit of the age of the craters on the equilibrium timescale of the radiolytic sulfur cycle on Europa’s trailing hemisphere.
Additionally, we find that the dark and red material seen in the craters and proximal ejecta of Pwyll and Manannán show the spectroscopic signature of hydrated, presumably endogenic salts.
This suggests that the irradiation-induced darkening and redenning of endogenic salts thought to occur on Europa’s trailing hemisphere has already happened at Pwyll and Manannán, thereby placing an upper limit on the timescale by which salts are irradiation reddened.
Sulfuric acid, salt, and water-ice concentration maps for Pwyll and Manann´an craters. Panels (a) and (e) show the Galileo/SSI images of Pwyll crater, with the estimated sulfuric acid abundance from the corresponding NIMS cubes displayed in panels (b) and (f), the salt abundance in panels (c) and (g), and the water-ice abundance in panels (d) and (h). The crater rim is shown as the dashed circle, the extent of the dark proximal ejecta is indicated by the solid circle, and the bright white ejecta blanket is outlined in solid black. Likewise, panel (i) shows the SSI image of Manann´an crater and the corresponding sulfuric acid, salt, and water-ice maps are shown in panels (j), (k), and (l), respectively. The extent of the dark ejecta is indicated by the solid circle, and the bright white ejecta blanket is outlined in black. The maps report the percent contribution of sulfuric acid, salts, or water-ice to the best-fit linear spectral model for each NIMS pixel. Note the different scale bars between the Pwyll and Manann´an maps. Both Pwyll and Manann´an craters and their ejecta appear to be depleted in sulfuric acid relative to nearby older terrains, suggesting that the radiolytic sulfur cycle has not yet had enough time to reach an equilibrium concentration of H2SO4 at either crater. At both Pwyll and Manann´an, the crater and dark proximal ejecta appear to be enriched in salts relative to the bright white ejecta blanket, suggesting that the dark material exhumed by the impacts is relatively salt-rich. The dark albedo and reddish coloration seen in the SSI images of both craters suggests that this salty material has already been irradiation reddened. As seen in panels (j) and (k), the nearby triple band, Belus linea, is significantly enhanced in salts and depleted in sulfuric acid relative to the background terrain. — astro-ph.EP
M. Ryleigh Davis, Michael E. Brown
Comments: 13 pages, 6 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2404.15474 [astro-ph.EP] (or arXiv:2404.15474v1 [astro-ph.EP] for this version)
Related DOI:
https://doi.org/10.3847/PSJ/ad3944
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Submission history
From: M. Ryleigh Davis
[v1] Tue, 23 Apr 2024 19:25:15 UTC (16,582 KB)
https://arxiv.org/abs/2404.15474
Astrobiology
