Space weathering

from Wikipedia, the free encyclopedia

Space weathering (also space weathering called; English space weathering ) describes the change in the surface of airless planetary solids such asteroids , moons and planet in outer space by the action of star winding (in the solar system, of the solar wind ), the cosmic rays , by the impact of meteorites and Micrometeorites as well as thermal stress. The weathering of space changes the chemical and physical properties of the planetary surface and leads z. B. on the Reddening phase , with the help of which the exposure age can be determined.

Processes

Sub-processes of space weathering

The following processes contribute to space weathering:

Thermal stress

In the case of atmospheric planetary bodies, thermal stress occurs between the illuminated day and unlit night side of rock bodies of any size. As a result of the cracks that then spread, all surface rocks disintegrate into dust particles ( regolith ) with a size of 0.1 mm.

Ionizing radiation

The UV and X-rays of the sun ionized and changed the chemical composition of the surface. Organic compounds on asteroids are z. B. reduced to a type of bitumen , which leads to a low albedo and a shift in the color index to red. These reactions are also caused by the gamma rays from cosmic rays.

Sputtering

Electrically charged particles from the solar wind and ions from cosmic rays lead to sputtering , in which atoms from the solid are accelerated to their escape speed. High-energy particles from cosmic rays also have this effect.

Micrometeorites

The impact of micro-meteorites leads to the evaporation of these meteorites and the regolith. Most of the heaviest atoms remain on the surface, especially iron. Iron can be detected in the lunar and metorite dust in the form of a nanophase and also spectroscopically.

Rejuvenation of the surface

Bright spots have been detected on the surfaces of asteroids and moons. These are caused by the rearrangement of the regolith e.g. B. by the impact of meteorites and landslides . With asteroids, the YORP effect leads to an acceleration of the rotation up to the centrifugal force limit . This leads to a displacement of the dust and the exposure of unexposed areas. These phenomena make it difficult to determine the age of unresolved surfaces of planetary bodies. Rejuvenation of the surface of an asteroid can also be caused by seismic shaking due to a close encounter with a planet. This is believed to be the cause of the rare Q class asteroids.

The Type S / Common Chondrite Puzzle

Almost 80% of the meteoroids belong to the class of common chondrites . Their spectrum differs significantly from that of the most common class of asteroids of the type S and the related sub-types, which all consist predominantly of silicates like the common chondrites. This previously unexplained difference was referred to as the S-type / ordinary-chondrite puzzle (English S-type-ordinary-chondrites conundrum ).

The riddle is now considered solved; the observed effect is explained by the weathering of space. When entering the earth's atmosphere, ablation occurs , which removes the changed surface and exposes the base material, which has not been influenced by weathering. The type S asteroids are therefore ordinary chondrites with a space-weathered surface.

literature

  • SE Schröder, HU Keller, S. Mottola, F. Scholten, F. Preusker, K.-D. Matz, S. Hviid: Variegation and space weathering on asteroid 21 Lutetia . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1701.00943v1 (English).
  • Pierre Vernazza, Brigitte Zanda, Tomoki Nakamura, Edward Scott, Sara Russell: The Formation and Evolution of Ordinary Chondrite Parent Bodies . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1611.08734v1 (English).
  • Heather M. Kaluna, Joseph R. Masiero, Karen J. Meech: Space Weathering Trends Among Carbonaceous Asteroids . In: Astrophysics. Solar and Stellar Astrophysics . 2015, arxiv : 1509.01632v1 (English).
  • DI Shestopalov, LF Golubeva, EA Cloutis: Space weathering of asteroids . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1211.6275v1 (English).
  • S. Marchi et al .: On the puzzle of space weathering alteration of basaltic asteroids . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1009.0179v1 (English).

Individual evidence

  1. ↑ Abhijit Basu: Nanophase Fe 0 in lunar soils , Journal of Earth System Science, June 2005.