Surfaces of Planets and Satellites Weakly Active Surfaces

Except for the Sun and the giant planets, which have no surfaces in the generally accepted sense, the surfaces of all bodies in the Solar System are still subject to impact cratering and gradation, but only some of them now experience (cryo)volcanism or tectonic processes to any significant extent, and in this sense are active. This suggests an obvious grouping of the surfaces into two sorts, and this is the basis on which Chapters 7 and 8 are organised. Thus, Chapter 7 describes surfaces that are now weakly active or inactive, and Chapter 8 describes those that are much more strongly active. The bodies with active surfaces are the Earth and Venus - the two largest terrestrial planets - and some of the larger satellites. The bodies with weakly active surfaces range in size from Mars down to the smallest bodies in the Solar System, though we shall concentrate on the larger ones. Broadly speaking, a body has a weakly active or inactive surface because its interior has cooled to the point where its lithosphere is now too thick to allow (cryo)volcanism or tectonic processes to occur.

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