Nicole Spaun

The Formation and Evolution of the Hydrological Cycle on Europa

I. Introduction:
It has long been known that Europa has a dominantly water ice surface. Recent Galileo Magnetometer results have suggested the presence of an underlying liquid ocean and Galileo Near Infrared Spectrometer results indicate the salts are present on Europas surface, which suggests a more elaborate chemical differentiation than the simple extraction of ice from a rocky body. Further, a tenuous oxygen atmosphere has been discerned at Europa. The paucity of observed impact craters indicates that Europa has a young surface age, where wide-scale resurfacing occurred. Taken together, this information implies that a complex hydrological cycle is at work within and upon Europa.

II. Questions and approaches:

A. How did Europa initially gain its water?
1. Accretion
2. Comets?

B. How did Europa chemically and mechanically differentiate?
1. Aqueous differentiation of chondrites [Kargel, 1991; Finale et al., 1977, 1998]
2. Geophysical approaches [e.g., Finale et al., 1977; Cassen et al., 1979, 1980]
a. Did this create a water-rich layer? Iron core, silicate mantle, H2O crust model [Spaun and Head, 2000; Kargel et al., 2000]
b. Did this create several water-rich layers? e.g., Core, hydrated mantle, H2O crust

C. What internal processes can be at work (or have worked) to create a
hydrological cycle that would yield such resurfacing?
1. Conduction
2. Solid-state Convection
3. Mantle-crust interactions (e.g. hydrothermal sources, multi-layer convection)
4. Volcanism

D. What external processes are occurring at Europa's surface?
1. Radiolysis
2. Sublimation
3. Sputtering
4. Micro-meteorite bombardment/implantation

E. How do these external processes affect the resurfacing of Europa?

F. Synthesis: What are the possible courses of the Europan hydrological cycle?