Rille
A rille is used to describe any of the long, narrow depressions in the lunar surface that resemble channels. Typically a rille can be up to several kilometers wide and hundreds of kilometers in length. The term was derived from the German word for furrow or groove, and was most likely introduced by the astronomer Johann Schröter in his Selenographische Fragmente. The latin terms rima or rimae are also (more accurately) used for naming a rille or rilles.
Missing image
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Rimae on the floor of Gassendi crater, from Apollo 16.
There are three types of rille found on the lunar surface:
- Sinuous rilles meander in a curved path like a mature river, and are commonly thought to be the remains of collapsed lava tubes or extinct lava flows. They usually begin at an extinct volcano, then meander and sometimes split as they are followed across the surface.
- Arcuate rilles have a smooth curve and are found on the edges of the dark lunar maria. There are believed to form when the lava flows that created a mare cools, contracts, and sinks.
- Straight rilles follow long, linear paths and are believed to be grabens. That is, a section of the crust that has sunk between two parallel faults. These can be readily identified when they pass through craters or mountain ranges.
References
- Ewen A. Whitaker, Mapping and Naming the Moon, Cambridge University Press, 1999, ISBN 0521622484.