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Becker, T. M., Retherford, K. D., Roth, L., Hendrix, A. R., McGrath, M. A. and Saur, J. (2018). The Far-UV Albedo of Europa From HST Observations. J. Geophys. Res.-Planets, 123 (5). S. 1327 - 1343. WASHINGTON: AMER GEOPHYSICAL UNION. ISSN 2169-9100

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Abstract

We present an analysis of Europa's far-UV spectral albedo using observations during the 1999-2015 time period made by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. Disk-integrated observations show that the far-UV spectrum in the similar to 130 to 170-nm range is relatively flat or slightly blue (increasing albedo with decreasing wavelength) for the studied hemispheres: the leading, trailing, and anti-Jovian hemispheres. At Lyman- (121.6nm), the albedo of the trailing hemisphere continues the blue trend, but it reddens for the leading hemisphere. Also at this wavelength, the albedo of the leading hemisphere, which is higher than the trailing hemisphere at near-UV and visible wavelengths, is lower than the trailing hemisphere, exhibiting spectral inversion. We find no evidence of a sharp water-ice absorption edge at 165nm on any hemisphere of Europa, which is intriguing since such an absorption feature has been observed on the icy Saturnian satellites. Plain Language Summary We used observations spanning from 1999 to 2015 obtained by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope to study the surface reflectance of Europa at far-ultraviolet (UV) wavelengths. We find that Europa has a low reflectance in the UV and that there is little variation in the surface brightness at most of the UV wavelengths. When observed at visible wavelengths, one of Europa's hemispheres is brighter than the other, but at the UV wavelength of 121.6nm, the hemisphere brightness is reversed. We also find that Europa looks different from the icy moons of Saturn at far-UV wavelengths.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Becker, T. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Retherford, K. D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roth, L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hendrix, A. R. UNSPECIFIED UNSPECIFIED UNSPECIFIED McGrath, M. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Saur, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-187506
DOI:	10.1029/2018JE005570
Journal or Publication Title:	J. Geophys. Res.-Planets
Volume:	123
Number:	5
Page Range:	S. 1327 - 1343
Date:	2018
Publisher:	AMER GEOPHYSICAL UNION
Place of Publication:	WASHINGTON
ISSN:	2169-9100
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language PHASE CURVE ANALYSIS; GALILEAN SATELLITES; ULTRAVIOLET; SURFACE; REFLECTANCE; GANYMEDE; HST/STIS; AURORA; CONSTRAINTS; WAVELENGTHS Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18750