Europa

Europa’s H2O2: Temperature Insensitivity and a Correlation with CO2

By Keith Cowing

Status Report

astro-ph.EP

August 29, 2024

Filed under astro-ph.EP, astrochemistry, Europa, hydrogen peroxide, icy wold, Infrared Telescope Facility, JWST, Keck Observatory, Ocean world, Spectroscopy

Europa’s H2O2: Temperature Insensitivity and a Correlation with CO2 — A] Example Keck NIRSPEC slit obtained on February 24, 2016, when 18.6◦W (labeled with the black dot) is in the morning (∼13 hours prior to local noon in Europa’s ∼85-hour day, estimated ∼103 K). [B] Example Keck NIRSPEC slit obtained on February 25, 2016, when the same region (18.5◦W; labeled with the red dot) is in the afternoon (∼16 hours after local noon in Europa’s ∼85-hour day, estimated ∼115 K). [C] Corresponding reflectance spectra for this location in the morning (in black) and in the afternoon (in red). Dashed gray lines outline the H2O2 band. Second-order polynomial continua are indicated by the dashed curves of the same color as the spectrum. Continuum-removed absorptions are included and show nearly overlapping absorptions. A ∼12 K temperature increase over 24 hours is estimated from the thermal model of Trumbo et al. (2017a). This temperature change results in a negligible -3.1% change in the integrated band areas. Leading chaos regions are outlined in black (Leonard et al. 2024). Background basemap credit: USGS (2002). — astro-ph.EP

H₂O₂ is part of Europa’s water-ice radiolytic cycle and a potential source of oxidants to Europa’s subsurface ocean. However, factors controlling the concentration of this critical surface species remain unclear.

Though laboratory experiments suggest that Europa’s H₂O₂ should be concentrated in the coldest, most ice-rich regions toward the poles, Keck adaptive optics observations have shown the strongest H₂O₂ signatures in comparatively warm, salt-bearing terrain at low latitudes.

As a result, it was suggested that the local non-ice composition of these terrains — particularly hypothesized enrichments of CO₂ — may be a more dominant control on H₂O₂ than temperature or water-ice abundance.

Here, we use observations of Europa from the NASA Infrared Telescope Facility, Keck Observatory, and JWST to disentangle the potential effects of temperature and composition. In order to isolate the effect of temperature on Europa’s H₂O₂, we use the ground-based observations to assess its response to temperature changes over timescales associated with Europa’s daily eclipse and diurnal cycle.

We use JWST Cycle 1 data to look for any geographic correlation between Europa’s H₂O₂ and CO₂. Both changes in Europa’s 3.5-μm H₂O₂ absorption band from pre to post eclipse and across a local day suggest minimal effects of the local temperature on these timescales.

In contrast, the JWST observations show a strong positive correlation between Europa’s H₂O₂ and CO₂ bands, supporting the previously suggested possibility that the presence of CO₂ in the ice may enhance H₂O₂ concentrations via electron-scavenging.

Peiyu Wu, Samantha K. Trumbo, Michael E. Brown, Katherine de Kleer

Comments: 17 pages, 4 figures, Accepted to the Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2408.14639 [astro-ph.EP] (or arXiv:2408.14639v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2408.14639
Focus to learn more
Submission history
From: Peiyu Wu
[v1] Mon, 26 Aug 2024 21:06:19 UTC (37,497 KB)
https://arxiv.org/abs/2408.14639

Astrobiology, Astrochemistry,

Keith Cowing

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) 🖖🏻

Follow on Twitter