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Session 19 - Solar & Planetary Systems.
Display session, Monday, January 13
Europa is the most enigmatic of the Galilean satellites, due to its high albedo (0.7), indicating the presence of surface water ice and/or frost, its high density (3 g/cm^3), characteristic of a silicate body, and its relatively youthful surface when compared to Ganymede and Callisto. No craters larger than 20\,km wide have been found on Europa's surface, and very few of the 20\,km size. The absence of impact craters in a range comparable to those found on Ganymede and Callisto (between tens and hundreds of kilometers wide) implies that some sort of resurfacing mechanisms are responsible for concealing evidence of impacts of those magnitudes. Assuming a model of a silicate core surrounded by a liquid water layer and an ice crust 75--100\,km in depth, we used an impact simulation program to test the depths of cracks produced by impacts of basalt projectiles creating 200\,m, 2\,km, and 20\,km wide craters. We present graphs of crack depth as a function of time for a basalt projectile impacting an ice surface, and compare them with the crack depth as function of time for a basalt projectile impacting a basalt surface. It is doubtful that impacts of the size we tested could produce cracks that would propagate deep enough to reach the liquid water layer and produce the necessary flooding for resurfacing to take place. We also conclude that there is not enough mass melted from the ice layer upon impact to contribute significantly to flooding. We used an artificially low impact velocity (5\,km/s) to improve the numerical stability of our model. The impactor sizes were then scaled to the velocities appropriate to Europa (\sim20\,km/s). More realistic velocities need to be tested. We plan to carry out further testing of larger impacts at velocities as close as possible to the calculated impact velocity of projectiles on Europa, 19.43\,km/s.
Program listing for Monday