Jovian System Data Analysis Program

Cover Page/Proposal Summary

ROSS-99    NRA 99-OSS-01

Date Due: 5/5/99

We propose a focused analysis of Europa's cratering record, using GEM images plus state-of-the-art numerical, dynamical modeling. We wish to understand the absolute chronology and distribution of surface ages on Europa and to extend these insights to the cratering chronology and impactor populations in the Jovian system. It is tantalizingly possible that Europa has some very young localities. Unlike the overlapping secondary patterns on the Moon, Europa's widely separated large impacts permit study of distal secondaries with minimal ambiguity, enabling us to separate primary from secondary crater populations. By defining the primary crater population, we can establish cratering ages for small units on Europa and derive the frequency of surface units of various ages. We can also learn whether there is a deficit of small cometary impactors, as has been suggested. We also propose to study the longitudinal (and latitudinal) crater distributions in order to infer, for example, the origin of impactors. Leading/trailing asymmetry in crater densities may be smeared or non-existent, depending on the degree of crustal slippage, as suggested from orientations and colorations of lineaments. We will perform numerical simulations of the dynamics of potential impactor populations, which will also reveal the potential role of other planetocentric debris (e.g. from SL9-like breakups), which may otherwise masquerade as primary craters. GEM has augmented Galileo's nominal mission imaging of Europa by a factor of 5, making it vital to analyze GEM's clues about Europa's cratering history. Our research team marries the fresh perspectives of young researchers with the P.I.'s experience in researching planetary cratering and impactor populations. Our use of modern numerical simulations of dynamics, lacking in most previous studies, is vital for interpreting the new GEM cratering data.