A Galileo Multi-Instrument Study of Europa's Color Heterogenieties
J.C. Granahan, F.P. Fanale, T.B. McCord (STI and Univ. of Hawaii), G. Hansen (Univ. of Hawaii), R. Carlson, L. Kamp, D. Matson, A. Ocampo, W. Smythe (JPL), A.R. Hendrix, C.A. Barth (LASP), F. Leader, R. Mehlman (UCLA), R. Greeley, R. Sullivan (ASU), B.E. Clark, P. Helfenstein, J. Veverka (Cornell), P. Geissler (LPI), M.J.S. Belton (NOAO), K. Becker, T. Becker, D. Cook (USGS), Galileo NIMS, SSI, and UVS Teams
The present study combines data from the the Galileo Near Infrared
Mapping Spectrometer (NIMS), the Solid State Imager (SSI), and the
UltraViolet Spectrometer (UVS) to investigate the compositional
diversity of the surface of Europa. Three of the terrains studied
here (mottled terrain, linea, and trailing hemisphere dark terrain) were
known from Voyager results. Galileo revealed an additional terrain
(infrared bright plains) that represents bright Europan icy plains
materials with unusually large near infrared (890 and 990 nm) albedos
(Greeley et al. 1996).Our G1 orbit SSI/NIMS composite spectra show
that the mottled terrain possesses spectra which offset the dominant
water ice bands to slightly shorter wavelengths. Observations of the
linea taken during a NIMS E6 observation and a G1 SSI clear filter
image indicate that the linea and some dark dome-like features have a
spectral signature similar to that of the mottled terrain. This suggests
that the same darkening agent is the water ice contaminant for both
mottled terrain and the linea. The best spectral matches for this
component are evaporite, hydrated minerals which are produced as
aqueous weathering products. The trailing hemisphere dark terrain
of Europa has been studied using a G2 SSI color observation,
3 E4 NIMS , and 3 E4 UVS observations . The dark terrain on the trailing
hemisphere appears to mask the indigenous Europa surface albedo
and may be due to a form of sulfur material (a finding consistent
with previous Voyager and IUE studies). The infrared bright plains
were best observed in the G1 NIMS and SSI northern high latitude
observations. The infrared bright plains are interpreted to contain
purer water ice and/or water ice with larger grain sizes than the
immediate surrounding regions.