| arachnoid | A circular feature on the surface of Venus connected to other similar features by a web of fractures.
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| corona | (A) The outermost layer of the Sun’s atmosphere. Gases in the corona are tenuous and hot. (B) A circular feature on the surface of Venus. Coronae appear to be collapsed volcanic domes and can be as much as several hundred kilometers across. (C) A type of surface feature of Uranus’s satellite Miranda. Coronae consist ofparallel ridges and troughs producing a striped appearance. Coronaehave sharp boundaries.
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| intercrater plain | Smooth portions of the surface of Mercury that lie between and around clusters of large craters.
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| retrograde rotation | The westward rotation of a solar system body.
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| scarp | A cliff produced by vertical movement of a section of the crust of a planet or satellite.
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| shield volcano | A broad, gently sloped volcano built up by the repeated eruption of very fluid lava.
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| smooth plains | Widespread sparsely cratered regions of the surface of Mercury possibly having a volcanic origin.
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