Understanding the Composition of Europa's Surface in the Ultraviolet with New HST Observations
Abstract
Jupiter's moon, Europa, is an ocean world with an icy shell primarily composed of water ice. However, at ultraviolet (UV) wavelengths, the sharp signature of water ice typically detected near 165 nm in laboratory studies and on the icy satellites of Saturn is not present in Europa's spectrum. To investigate the lack of the water ice signature, we acquired mid-UV observations of Europa's leading, trailing, sub-Jovian, and anti-Jovian hemispheres using the Hubble Space Telescope in 2018 and 2019. The data have a spectral bandpass of ~165 nm - 310 nm with a spatial resolution of ~80 km/pixel.
We find that even on the visibly brighter, leading hemisphere, the Europa UV spectra slowly increase in reflectance with longer wavelengths instead of displaying the expected rapid rise in reflectivity near 165 nm for water ice. This may be explained by small amounts of contaminant within the water ice grains, a lag deposit on the uppermost layer of Europa's surface, radiation effects on the ice, or grain sizes. Additionally, the spectra display an absorption feature centered near 280 nm that peaks in strength on the apex of the trailing hemisphere, which has been previously attributed to SO2 implantation from the Io torus. We will present spatial maps of the strength of the 280 nm absorption feature and variations in the UV spectral slope across Europa's surface. We will also show our spectral modeling efforts to explain the unique observations of Europa's reflectance in the UV.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P53D3497B
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHERE;
- 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6221 Europa;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6282 Enceladus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS