Rille
From Wikipedia, the free encyclopedia
Rille is typically used to describe any of the long, narrow depressions in the lunar surface that resemble channels. (It is pronounced the same as a secondary name for a river in Normandy in France. See Risle.) Typically a rille can be up to several kilometers wide and hundreds of kilometers in length. However, the term has also been used loosely to describe similar structures on a number of planets in the solar system, including Mars, Venus, and on a number of moons. All bear remarkable structural resemblance to each other.
Contents |
[edit] Etymology
The term was derived from the German word for furrow or groove, and was most likely introduced by the astronomer Johann Schroeter in his Selenographische Fragmente. The latin terms rima or rimae are also (more accurately) used for naming a rille or rilles.
[edit] Structures
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.
[edit] Formation
Precise causes of rilles have yet to be determined. Leading theories currently include erosion at some point in the stellar body's history, collapsed lava tubes, and tectonic activity/stresses. Similarity between rilles on the moon and similar structures on many planets in the solar system suggests a common causative mechanism, yet to be determined.
[edit] References
- Ewen A. Whitaker, Mapping and Naming the Moon, Cambridge University Press, 1999, ISBN 0-521-62248-4.
