H2O2 Within Chaos Terrain on Europa's Leading Hemisphere


A single N/S slit from our 2016 observations, which falls on the leading hemisphere and crosses both the most spectrally icy location on the surface (∼ 30◦ N, 90◦ W, Brown & Hand 2013) and the salty, low-latitude chaos region Tara Regio. Contrary to the hypothesis that Europa’s H2O2 should follow the cold, icy terrain of the upper latitudes, the 3.5 µm band appears anti-correlated with both temperature and ice availability. Instead, the strongest absorptions fall nearly perfectly within the outlined bounds of Tara Regio, with band areas more than twice that of the aforementioned ice-rich region. We show representative spectra from both locations to the right of the map, where the dashed red lines outline the H2O2 band. Second-order polynomial continua are indicated by the dashed black curves. We also include the continuum-removed absorptions to ease comparison of the band strengths, although the differences are readily apparent in the spectra themselves. Both spectra are normalized to their individual peaks in the 3.6–3.7 µm region.

Hydrogen peroxide is part of an important radiolytic cycle on Europa and may be a critical source of oxidants to the putative subsurface ocean.

The surface geographic distribution of hydrogen peroxide may constrain the processes governing its abundance as well as its potential relevance to the subsurface chemistry. However, maps of Europa's hydrogen peroxide beyond hemispherical averages have never been published. Here, we present spatially resolved L-band (3.16 - 4 μm) observations of Europa's 3.5 μm hydrogen peroxide absorption, which we obtained using the near-infrared spectrometer NIRSPEC and the adaptive optics system on the Keck II telescope. Using these data, we map the strength of the 3.5 μm absorption across the surface at a nominal spatial resolution of ∼300 km.

Though previous disk-integrated data seemed consistent with the laboratory expectation that Europa's hydrogen peroxide exists primarily in its coldest and iciest regions, we find nearly the exact opposite at this finer spatial scale. Instead, we observe the largest hydrogen peroxide absorptions at low latitudes on the leading and anti-Jovian hemispheres, correlated with chaos terrain, and relative depletions toward the cold, icy high latitudes. This distribution may reflect the effects of decreased hydrogen peroxide destruction due to efficient electron scavenging by CO2 within chaos terrain.

Samantha K. Trumbo, Michael E. Brown, Kevin P. Hand
(Submitted on 2 Aug 2019)

Comments: 7 pages, 2 figures, accepted for publication in the Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1908.01093 [astro-ph.EP] (or arXiv:1908.01093v1 [astro-ph.EP] for this version)
Submission history
From: Samantha Trumbo
[v1] Fri, 2 Aug 2019 23:39:44 UTC (1,272 KB)
https://arxiv.org/abs/1908.01093
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