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Kebira Crater
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Kebira Crater ((アラビア語:فوهة كبيرة)) is the name given to a circular topographic feature that was found in 2007 by Farouk El-Baz and Eman Ghoneim using satellite imagery, Radarsat-1, and Shuttle Radar Topography Mission (SRTM) data in the Sahara desert. This feature straddles the border between Egypt and Libya. The name of this feature is derived from the Arabic word for "large", and also from its location near the Gilf Kebir ("Great Barrier") region in southwest Egypt. Based solely on their interpretations of the remote sensing data, they argue that this feature is an exceptionally large, double-ringed, extraterrestrial impact crater. They suggest that the crater's original appearance has been obscured by wind and water erosion over time. Finally, they speculated that this feature might be the source of the yellow-green silica glass fragments, known as "Libyan desert glass", that can be found across part of Egypt's Libyan Desert. They neither conducted any fieldwork at this feature nor studied any samples collected from it.〔El-Baz, F., and E. Ghoneim (2007) ''Largest crater shape in the Great Sahara revealed by multi-spectral images and radar data.'' International Journal of Remote Sensing. 28(2): 451–458.〕 However, the Kebira Crater is currently not listed in the Earth Impact Database.〔Anonymous (nd) (''Africa'' (Impact Craters), ) (Earth Impact Database ), (Planetary and Space Science Centre ), University of New Brunswick, New Brunswick, Canada.〕 Field trips to investigate the feature have found no supporting evidence. The "central uplift" clearly retains the horizontal bedding of the surrounding sandstone tableland, providing clear evidence against a possible impact origin.〔Brügge. N. (2012) (''A not credible message to a so named crater "Kebira." ) in (Geology of the Libyan Desert ), accessed 20 October 2013.〕〔Orti, L., M. Di Martino, M. Morelli, C. Cigolini, E. Pandeli, and A. Buzzigoli (2008) ''Non-impact origin of the crater-like structures in the Gilf Kebir area (Egypt); implications for the geology of eastern Sahara.'' Meteoritics & Planetary Science 43(10):1629-1639.〕〔Di Martino M., L. Orti, L. Matassoni, M. Morelli, R. Serra, and A. Buzzigoli (2006) (''Non-impact Origin of the Craterfield in the Gilf Kebir Region (SW Egypt)'' ), online PDF file.〕
==Characteristics==
According to their interpretations of Landsat Enhanced Thematic Mapper Plus (ETM + ) images, Radarsat-1 data, and SRTM data, El-Baz and Ghoneim described this circular feature as having a central peak, an inner ring, and discontinuous outer rim. The hypothetical outer rim is 31 kilometres (19 mi) in diameter.〔 This feature consists of well-cemented, coarse- and fine-grained sandstones of the Gilf Kebir and Wadi Malik formations.〔Longinelli, A., G. Sighinolfi, V. de Michele, and E. Selmo (2011) ''δ18O and chemical composition of Libyan Desert Glass, country rocks, and sands: New considerations on target material.'' Meteoritics & Planetary Science. 46(2):218-227.〕
Were this an impact structure, it would be bigger than the largest confirmed impact structure in the region, the Oasis crater in Libya, which is approximately half the size, with a diameter of approximately 18 kilometres (11 mi).〔 It is estimated that a meteorite large enough to have created a Kebira-sized impact structure would have been roughly 1 kilometre (0.75 mi) in diameter.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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