[Previous] | [Session 17] | [Next]
J. Eluszkiewicz (Atmospheric and Environmental Research, Inc.)
The presence of a regolith on Europa is likely to pose a serious obstacle to the search for an Europa ocean using a sounding radar, provided that 1. The regolith contains cavities with sizes comparable to the radar wavelength and 2. The regolith is sufficiently thick (a few hundred meters or more). The size of cavities is hard to estimate, but it is likely that both meteoritic bombardment and tidal flexing will produce pores and cracks with a wide size distribution, including those that would strongly scatter the radar signal. Assuming enough regolith production, the thickness of the regolith can be estimated by considering the depth at which pores and cracks are annealed by gravitational compaction. Using rheological data for the creep of ice and making plausible assumptions about the temperature distribution at depth, it is estimated that the uppermost 1 km of Europa's crust is likely to retain significant porosity. This layer will attenuate the radar signal by many orders of magnitude, in addition to the temperature- and composition-dependent absorption processes considered in previous assessments of the radar penetration. Consequently, a radar experiment for the proposed Jupiter Icy Moon Orbiter mission should focus on studying the structure of Europa's regolith, rather than searching for an ocean (which even under the most optimistic scenarios is located at depths greater than a few kilometers).
[Previous] | [Session 17] | [Next]
Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.