Metamorphism and Mixed Material Types in a Jovian Satellite?

K. S. Jarvis (LMSMSS), F. Vilas (NASA JSC), S. M. Larson (U. Ariz.), M. J. Gaffey (RPI)

Rotationally resolved visible/near IR reflectance spectra of the Jovian satellite J6 Himalia provide spatial coverage of both sides of J6 and indicate there are no significant mineralogical differences between the two sides. The tight cluster of satellites (J6, J7, J10, J13) suggests they were once a single parent body. J6 and J7 are thought to consist of C-type material while J10 has been interpreted as either C- or D-type material. Among low-albedo asteroids, mixed classes derived from a single parent body are not unprecedented as the Veritas family may contain both C- and D-class asteroids (DiMartino et al., 1997). Where did J6's parent body originate? The most favored theory suggests ejection and capture of a C-class asteroid from the main belt. Because of its diameter and believed heliocentric origin, some indication of thermal metamorphism is expected. Thermal metamorphism may be identifiable by a shallowing of the UV absorption (Hiroi et al., 1996) for which we are currently testing our data. Limiting factors rendering any conclusions cautionary are the degree of regolith gardening and percentage of water. As J6 is part of a closely-grouped family, others in this group may also display thermal metamorphism. If J6 consists primarily of the (rubble pile?) core of the parent body, then the remaining three moons may contain less altered material. (This work supported by NASA Planetary Astronomy Program.)