Regolith
Regolith (from ancient Greek ῥῆγος rhēgos "[colorful] blanket" and λίθος líthos "stone") is a blanket made of loose material, which has formed on rocky planets in the solar system through various processes over an underlying raw material.
Term in the sense of geomorphology
In the geomorphology referred regolith subterranean material as a result of physical and chemical weathering exclusively on the spot ( in situ ) of a pending emerged source rock. A redistribution did not take place or only took place over a very short distance, for example through slight creeping on the slope . Regolith differs in this from sediment , i.e. from sediment that was previously transported over a certain distance by flowing liquids or gases or by gravity.
Perceptions of what to call regolith differ to a certain extent. Some geoscientists include the saprolite , which still shows the structure of the parent rock, while others do not.
Term in the sense of planetology
In planetology or astrogeology , regolith is non-terrestrial loose material on the surface of rock planets i. w. S. (see e.g. → moon regolith ). In the case of objects in the inner solar system , the regolith actually consists only of silicate material , and in the case of objects in the outer solar system, it also consists of ice .
In contrast to the regolith in the sense of geomorphology, this regolith, with the exception of thermal processes , was not created by processes that are summarized under the umbrella term weathering in the actual - that is, earthly - sense. The conditions on the surface of almost all celestial bodies in the solar system differ fundamentally from earthly conditions due to the absence of liquid water and the absence of a (dense) atmosphere.
The extraterrestrial loose material called regolith was therefore largely created by mechanical destruction in the course of the impacts of meteorites and micrometeorites and by the action of high-energy radiation (solar and galactic cosmic radiation ). This is also known as space weathering.
In the case of smaller asteroids , on the other hand, it is assumed that their “regolith” was formed primarily by accretion , i.e. H. by “picking up” matter as a result of low-speed collisions. Such a body is also called accretionary Megaregolith (accretionary megaregolith) referred. Presumably it represents an early stage in planetary development, which the great rocky planets of the solar system, including the earth, once went through. Accretionary regolith has nothing in common genetically with either the terrestrial regolith or that of the moon or Mars. It is not a matter of secondary material, as on earth and moon, but of primary material which, due to the low gravity of the body, has never been subject to compaction , melting and differentiation. Nevertheless, accretionary regolith is also further modified by collisions and radiation.
literature
- Frank Ahnert: Introduction to Geomorphology. 3rd, updated and supplemented edition. Eugen Ulmer Verlag, Stuttgart 2003, ISBN 3-8001-2813-6 .
- Harald Zepp: Geomorphology. General geography floor plan . 4th edition. UTB , Stuttgart 2008, ISBN 978-3-8252-2164-5 .
- Kevin R. Housen: Regoliths on small bodies in the Solar System. In: Annual Review of Earth and Planetary Sciences. Vol. 10, 1982, pp. 355-376, doi: 10.1146 / annurev.ea.10.050182.002035 (alternative full text access : ResearchGate )
- Lucy-Ann McFadden, Paul Weissman, Torrence V. Johnson (Eds.): Encyclopedia of the Solar System. 2nd Edition. Associated Press Elsevier, San Diego (CA) / London / Amsterdam 2007, ISBN 978-0-12-088589-3 .
