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IMAGE OF AOROUNGA CRATER
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Possible String of Impact Craters, Chad
The impact of an asteroid or comet several hundred million years
ago left scars in the landscape that are still visible in this
spaceborne radar image of an area in the Sahara Desert of
northern Chad. The concentric ring structure left of center is
the Aorounga impact crater with a diameter of about 17 kilometers
(10.5 miles). Scientists are using radar images to investigate
the possibility that Aorounga formed as part of a multiple impact
event. A proposed second crater, similar in size to the main
structure, appears as a circular trough surrounding a central
peak in the center of the image.
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Aorounga Crater Sahara Desert, Chad SIR-C Radar Image April 18-19, 1994
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A third structure, also about
the same size, is seen as a dark, partial circular trough with a
possible central structure in the right center of the image. The
proposed crater "chain" could have formed when a 1 km to 2 km
(0.5 mile to 1 mile) diameter object broke apart before impact.
The dark streaks are deposits of windblown sand that migrate
along valleys cut by thousands of years of wind erosion. Radar
imaging is a valuable tool for the study of desert regions
because the radar waves can penetrate thin layers of dry sand to
reveal details of geologic structure that are invisible to other
sensors. The image was acquired by the Spaceborne Imaging Radar-
C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on April 18 and
19, 1994, onboard the space shuttle Endeavour. The area shown is
45 kilometers by 61 kilometers (28 miles by 38 miles) and is
centered at 19.25 degrees north latitude, 19.25 degrees east
longitude. North is toward the upper right. The colors are
assigned to different radar frequencies and polarizations as
follows: red is L-band, horizontally transmitted and received;
green is C-band, horizontally transmitted and received; and blue
is C-band, horizontally transmitted, vertically received. SIR-
C/X-SAR, a joint mission of the German, Italian and United States
space agencies, is part of NASA's Mission to Planet Earth
program.
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