Morokweng impact structure
The Morokweng crater (or Morokweng impact structure) is an impact crater buried beneath the Kalahari Desert near the town of Morokweng in South Africa's North West province, close to the border with Botswana.[1]
The crater, formed by an asteroid 5 to 10 km (3.1 to 6.2 mi) in diameter, is at least about 70 km (43 mi) in diameter and the age is estimated to be 145.0 ± 0.8 million years, placing it at the Jurassic–Cretaceous boundary. Discovered in 1994, it is not exposed at the surface, but has been mapped by magnetic and gravimetric surveys. Core samples have shown it to have been formed by the impact of an L chondrite asteroid.[2]
In May, 2006, a group of scientists drilling into the site announced the discovery of a 25 cm (9.8 in)-diameter fragment of the original asteroid at a depth of 770 m (2,530 ft) below the surface, along with several much smaller pieces a few millimetres across at other depths. This discovery was unexpected, since previous drillings on large impact craters had not produced such fragments, and it was thought that the asteroid had been almost entirely vaporised.[3] Some of the fragments can be seen in the Antenna Wing of London's Science Museum.
References
- ^ "Morokweng". Earth Impact Database. Planetary and Space Science Centre University of New Brunswick Fredericton. Retrieved 2012-01-14.
- ^ Christian Koeberl; Bernhard Peucker-Ehrenbrink; Wolf Uwe Reimold. "Meteoric component in impact melt rocks from the Morokweng, South Africa, impact structure: An OS isotopic study" (PDF). Lunar and Planetary Science. 31.
- ^ Maier, WD; Andreoli MA; McDonald I; Higgins MD; Boyce AJ; Shukolyukov A; Lugmair GW; Ashwal LD; Graser P; Ripley EM; Hart RJ (May 11, 2006). "Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa". Nature. 441 (7090): 203–6. Bibcode:2006Natur.441..203M. doi:10.1038/nature04751. PMID 16688173.
- Morelle, Rebecca (10 May 2006). "Relic of ancient asteroid found". BBC News. Retrieved 2006-05-31.
- "Meteorite survivor unearthed". news@nature.com. Nature Publishing Group. 10 May 2006. Retrieved 2006-05-31.
External links
26°28′00″S 23°32′00″E / 26.466667°S 23.533333°E
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