Surface and Internal Structure of Icy Satellites

There is a great diversity of surface morphology of icy satellites (Fig. 9.1). Callisto and Mimas are rather heavily cratered with a paucity of tectonic features. On the other hand, Europa displays global tectonic features a network of fine, curving fissures covers its surface. Ganymede and Tethys are of an inter- 

The only observational constraint on the internal structure of satellites is density. The bulk composition (rock to ice ratio) of icy satellites is obtained by comparing their density vs. radius relationship with model curves calculated by Lupo and Lewis [6] as shown in Fig. 9.2. From this comparison, we can estimate the rock to ice (to pore) ratio of the satellites. 

Evolution of the Solar System Importance of Impact Process 

The planetesimals accumulate mass through mutual collisions and grow to form planets. The collision velocity depends on the size of the planetesimals. The collision velocity of the planetesimals for m = 1015 kg is almost the same as the random velocity of corresponding planetesimals, about 10 m/s. The reason 

When the mass of the planetesimals exceeds 1024 kg, the escape velocity becomes larger than the random velocity. As a result, the collision velocity is a few km/s. With increasing collision velocity, cratering, vaporization, and fragmentation rather than growth of the planetesimals becomes dominant. Therefore, investigation of impact phenomena over a wide range of velocities is essential for discussion of the formation and disruption of planets. Especially, it becomes a key as to whether the velocity of impact ejecta exceeds the escape velocity of the planetesimal or protoplanet. 

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