DPS Meeting, Madison, October 1998
Session 38. Europa II
Contributed Oral Parallel Session, Thursday, October 15, 1998, 10:10-11:40am, Madison Ballroom C

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[38.02] A Composition Study of Europa's Impact Scars (Tyre and Pwyll) as Seen By Galileo NIMS and SSI

J. Granahan, F. Fanale (Science and Technology International), R. Greeley, S. Kadel, F. Chuang (A.S.U.), R. Pappalardo, J. W. Head, III (Brown Univ.), J. Moore (NASA Ames), E. Asphaug (U.C. Santa Cruz), L. Kamp, W. D. Smythe, R. W. Carlson (J.P.L.), Galileo NIMS Team , Galileo SSI Team

Tyre's morphology suggests that the impact occurred on a target with a brittle elastic lithosphere underlain by a liquid or highly ductile material. Infrared data show this region and the impact scar dominated by water ice with some features such as linea, some lenticulae, and a few portions of Tyre's concentric ring structure possessing a subtle asymmetric spectral features near 1.48 and 2.0 micrometers in wavelength. Using linear spectral mixing models of NIMS data or Rhadamanthys Linea and that of water ice, we have determined that these spectra can be matched with approximately 10% Rhadamanthys Linea material and 90% water ice. A candidate for the Rhadamanthys Linea material are saline hydrates. Why is this signature so weak? The infrared data has a resolution of 6 km/pixel compared to the Rhadamanthys Linea observation with 2 km/pixel. Areal mixing of the spectra of water ice and the possible saline hydrate material could match the infrared observations. SSI observations also see red spectral material (also associated with Rhadamanthys Linea) in the concentric ring structure of Tyre not seen by NIMS. The morphology of Tyre suggests that the candidate saline hydrate material was derived from the fluid/highly ductile layers below.

Pwyll’s morphology implies that it impacted a brittle lithosphere overlying much less ductile material. Its long rays have a strong infrared water ice signature. Pwyll also possesses “dark” material within its crater which also possess infrared asymmetric features (described above). Linear spectra mixing models suggest that these “dark” materials may be 50/50 water ice and candidate saline hydrate material. As the infrared data has a resolution of 1.25 km/pixel, we are not seeing the same concentration of this candidate saline hydrate materials as seen in some linea. It does suggest that Pwyll impacted into a layer of material which maybe a salt/ice mixture.

The author(s) of this abstract have provided an email address for comments about the abstract: granahan@sti.hawaii.com

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