DPS 2001 meeting, November 2001
Session 35. Icy Galilean Satellites I: Geology and Geophysics
Oral, Chairs: W. Moore, J. Moore, Thursday, November 29, 2001, 4:40-6:10pm, Regency GH

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[35.02] Pits and Uplifts on Europa: Distribution and Characteristics

R. Greenberg, M.A. Leake, G.V. Hoppa, B.R. Tufts (LPL, U. Arizona)

Pits and uplift features are common in Galileo images of Europa. We have surveyed and mapped them in the broad swaths of 200-m resolution imagery obtained from Galileo for regional mapping. Patches of chaotic terrain are not included, because there is no a priori known genetic linkage with the pits and uplifts, because their topography is generally unclear, and because we had already surveyed chaotic terrain. Pits and uplifts come in a wide range of sizes, with numbers increasing greatly with decreasing size, down to the limits of resolution. The size distributions of pits and of uplifts are similar in the northern leading and southern trailing hemisphere, where the distribution is distinctly different from that in the southern leading and northern trailing hemisphere, suggesting an oblique, antipodal symmetry pattern, similar to that of chaotic and tectonic terrain. This pattern is suggestive of polar wander. Uplifts are usually polygonal or irregular in shape, and rarely are cracked.

Many generalizations of the earlier ``pits, spots, and domes" (PSD) taxonomy are not correct. Most of the type examples for PSDs were simply patches of chaotic terrain selected from a limited portion of their full size range. The use of the term lenticula to collectively describe PSDs is inconsistent with the IAU definition of lenticula: small dark spots seen at low resolution. Pits and uplifts do not correlate with lenticulae, although chaos often does. Generalizations regarding properties of PSDs that have been widely cited as primary evidence for convective upwelling in thick ice (including claims that uplifts are generally dome-shaped and often cracked; that pits and domes are regularly spaced; that there a typical diameter of ~~10 km) were premature and prove to be inconsistent with what is actually observed on Europa. Most pits' and uplifts' diameters are << 10 km, and if associated with diapirism or convective upwelling, the sources would have to be very shallow, less than a few kilometers deep. How they actually formed remains a matter of speculation.

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