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Mid-ultraviolet Hubble Observations of Europa and the Global Surface Distribution of SO₂

Becker, Tracy M. and Trumbo, Samantha K. and Molyneux, Philippa M. and Retherford, Kurt D. and Hendrix, Amanda R. and Roth, Lorenz and Raut, Ujjwal and Alday, Juan and McGrath, Melissa A. (2022) Mid-ultraviolet Hubble Observations of Europa and the Global Surface Distribution of SO₂. Planetary Science Journal, 3 (6). Art. No. 129. ISSN 2632-3338. doi:10.3847/psj/ac69eb.

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We present spatially resolved reflectance spectra of Europa’s surface in the wavelength range of 210–315 nm obtained by the Hubble Space Telescope Imaging Spectrograph in 2018 and 2019. These data provide the first high-quality, near-global spectral observations of Europa from 210 to 240 nm. They show that the reflectance of Europa’s leading, trailing, anti-Jovian, and sub-Jovian hemispheres is ∼5% near 210 nm, with varying spectral slopes across the mid-UV. This low albedo, even on the more “pristine” leading hemisphere, indicates a lack of the signature far-UV spectral edge characteristic of water ice. We detected and mapped a strong absorption feature at 280 nm that is consistent with an S–O bond that has previously been attributed to SO₂ on the surface, hypothesized to be formed through radiolytic processing of Iogenic sulfur ions that have been preferentially emplaced on Europa’s trailing hemisphere by Jupiter’s magnetic field. Our models show that small inclusions of SO₂ (0.1%) within the water ice are sufficient to produce the 280 nm feature without producing a feature at 4.07 μm, which has not been observed in ground-based spectral observations of Europa. This data set is the first to produce a spatially resolved, near-global map of the assumed SO₂ feature, which is primarily concentrated near the apex of the trailing hemisphere and correlated with large-scale darker regions in both the visible and the ultraviolet. This distribution is consistent with “cold” exogenic sulfur ion bombardment on Europa.

Item Type:Article
Related URLs:
URLURL TypeDescription
Becker, Tracy M.0000-0002-1559-5954
Trumbo, Samantha K.0000-0002-0767-8901
Molyneux, Philippa M.0000-0002-4725-4775
Retherford, Kurt D.0000-0001-9470-150X
Hendrix, Amanda R.0000-0002-0435-8224
Roth, Lorenz0000-0003-0554-4691
Raut, Ujjwal0000-0002-6036-1575
Alday, Juan0000-0003-1459-3444
McGrath, Melissa A.0000-0003-3562-6890
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 August 5; revised 2022 April 19; accepted 2022 April 22; published 2022 June 2. We thank the two anonymous reviewers for their improvements to this manuscript. This work is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program HST-GO-15095.001-A. This work was supported by NASA through the Europa Clipper Project.
Funding AgencyGrant Number
NASANAS 5-26555
Subject Keywords:Natural satellite surfaces; Planetary science; Remote sensing; Solar system; Galilean satellites
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Natural satellite surfaces (2208); Planetary science (1255); Remote sensing (2191); Solar system (1528); Galilean satellites (627)
Record Number:CaltechAUTHORS:20220606-736387000
Persistent URL:
Official Citation:Tracy M. Becker et al 2022 Planet. Sci. J. 3 129
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115043
Deposited By: George Porter
Deposited On:07 Jun 2022 14:55
Last Modified:07 Jun 2022 14:55

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