The Spatial Distribution of the Unidentified 2.07 μm Absorption Feature on Europa and Implications for its Origin

By Keith Cowing
Status Report
August 30, 2023
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The Spatial Distribution of the Unidentified 2.07 μm Absorption Feature on Europa and Implications for its Origin
(a) A map of Europa’s trailing hemisphere, showing a selection of four of the 29 considered “rings of constant radiolysis” outlined in black, which are used to determine whether the weak 2.07 µm absorption feature is associated with Europa’s large-scale geologic units. The chaos terrains are shown in red and Pwyll crater and its ejecta are orange. For each ring, projected detector pixels are shown and their assigned geologic unit indicated by color, where chaos terrains are dark red, Pwyll crater and its ejecta are orange, and the ridged plains are gray. (Europa map image credit: NASA/JPL/ Bj¨orn J´onsson). — astro-ph.EP

A weak absorption feature at 2.07 μm on Europa’s trailing hemisphere has been suggested to arise from radiolytic processing of an endogenic salt, possibly sourced from the interior ocean.

However, if the genesis of this feature requires endogenic material to be present, one might expect to find a correlation between its spatial distribution and the recently disrupted chaos terrains. Using archived near-infrared observations from Very Large Telescope/SINFONI with a ∼1 nm spectral resolution and a linear spatial resolution ∼130 km, we examine the spatial distribution of this feature in an effort to explore this endogenic formation hypothesis.

We find that while the presence of the 2.07 μm feature is strongly associated with the irradiation pattern on Europa’s trailing hemisphere, there is no apparent association between the presence or depth of the absorption feature and Europa’s large-scale chaos terrain. This spatial distribution suggests that the formation pathway of the 2.07 μm feature on Europa is independent of any endogenous salts within the recent geology. Instead, we propose that the source of this feature may simply be a product of the radiolytic sulfur cycle or arise from some unidentified parallel irradiation process.

Notably, the 2.07 μm absorption band is absent from the Pwyll crater ejecta blanket, suggesting that radiolytic processing has not had enough time to form the species responsible and placing a lower limit on the irradiation timescale. We are unable to find a plausible spectral match to the 2.07 μm feature within the available laboratory data.

M. Ryleigh Davis, Michael E. Brown, Samantha K. Trumbo

Comments: 12 pages, 3 figures, published in PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2308.13787 [astro-ph.EP] (or arXiv:2308.13787v1 [astro-ph.EP] for this version)
Journal reference: The Planetary Science Journal, 4, 148 (2023)
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Submission history
From: M. Ryleigh Davis
[v1] Sat, 26 Aug 2023 06:58:53 UTC (9,931 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻